MEASUREMENT OF DEFORMATION USING IMAGE ANALYSIS

Rhizlane LAHBABI, Patrick PERRE and Alcir BRANDAO

Laboratoire de Recherches en Sciences Forestières
ENGREF - 14 rue Girardet, 54042 NANCY Cedex

FRANCE

In order to specify the mechanical behaviour of solid materials, it is necessary to measure deformation. Classically, strain was measured using electrical strain gages, mechanical extensometers and Moiré method. The techniques are limited by instrumentation, sample geometry, fragility of some particular materials and instrument size.

In this work, an automatic method to quantify deformation directly from image analysis was developed. Under the hypothesis of small deformation when materials are subjected to compressive, tensile and/ or shear stress, a computer code allows to determine the strain field which separates two images (fig.1). The code was written in the principle of simplex method to minimize a function which depends on the gray level of both images.

The advantage of this technique is that the measurement is made without contacting. By applying the method on wood, it is possible to have the microscopic deformations (fig.2), and to find out the mechanical behaviour and shrinkage for each of anatomical elements.

This technique can also be used to study the mechanical behaviour of standing trees under load. In this connection, the deformation parameters will change: only have the curvature and displacement to be found (fig.3). This method also permits to characterize the mechanical properties of some elements of tree structure, or to follow the shape evolution of trees resulting from natural growth.

Key words: deformation, image analysis, simplex method, gray level, non contact.

References

Chao, Y.J. and Sutton, M.A. Measurement of strains in paper tensile specimen using computer vision and digital image correlation-Part 1: Data acquisition and image analysis system. Tappi 71.3 : 173-175 (1988).

Chao, Y.J. and Sutton, M.A. Measurement of strains in paper tensile specimen using computer vision and digital image correlation-Part 2: Tensile specimen. Tappi 71.4 : 153-156 (1988).

Choi, D., Thorpe, J.L. and Hanna, R.B. Image analysis to measure strain in wood and paper.
-Wood Sci. Technol. 25 : 251-262 (1991).
<figure><img src="image_119.png" /><figcaption>Fig.1 - Compressive test of oak: agreement between image analysis method and extensometer measurement.</figcaption></figure>

<figure><img src="image_120.png" /><figcaption>Fig.2 - Microscopic deformation under traction test for spruce</figcaption></figure>

<figure><img src="image_121.png" /><figcaption>Fig.3 - Non symmetric drying experiment of beech : curvature radius (R) measured by image analysis</figcaption></figure>
# SUMMARY OF VEGETABLE TRANSPLANT RESPONSE TO MECHANICAL CONDITIONING VIA BRUSHING

Joyce G. Latimer, Department of Horticulture, University of Georgia, Georgia Station, Griffin, GA 30223-1797 U.S.A.

By exploiting the effects of mechanical perturbation on plants, we can enhance plant habit, strength and structure under controlled environments. Since daminozide (Alar) is no longer registered for use on food crop plants in U.S.A., height control of greenhouse-grown vegetable transplants has been limited to restriction of water, nutrients, or both. Mechanical conditioning is the deliberate use of mechanical stress to provide an alternative means of height control of greenhouse-grown plants with the potential to produce a higher quality transplant (1). Brushing for regulation of plant growth and condition has been successful for a variety of vegetable crop species. In order to implement brushing in a commercial setting, we must identify the appropriate developmental stage for initiation of a brushing treatment and determine the responsiveness of various vegetable crop cultivars to brushing.

A brushing apparatus was designed for uniform application of the treatment across cultivars (2). Each vegetable species constituted a separate experiment using a split-plot design with three replications. The treatment was applied by brushing the upper one-third of seedlings with a wooden pole for about 1.5 min (80 or 40 strokes across a flat of plants) twice daily for one to three weeks depending on crop time. At the conclusion of treatment, all plants were rated for damage and six plants per subplot were harvested for measurement of stem length and shoot dry weight.

**Solanaceous crops.** Brushing initiated at the cotyledonary stage resulted in the shortest 'Sunny' tomato (*Lycopersicon esculentum*) transplants, with stem lengths 43% less than control, but treatment initiated at the first, second or third true-leaf stage also reduced stem length. All brushing treatments resulted in a 20% reduction in shoot dry weight. Damage was insignificant and plant appearance was excellent. Brushing initiated at the cotyledonary stage also resulted in the shortest pepper (*Capsicum annuum*) transplants, but over 40% of 'Marengo' plants and 90% of 'Jupiter' plants exhibited some damage from the treatment. Brushing initiated at the first or second true-leaf stage showed less reduction in stem growth but plant damage was still excessive. Brushing 'Pingtung Long' eggplant (*Solanum melongena*) seedlings at the cotyledonary, first, or second true-leaf stage resulted in good height control, stem lengths about 30% less than that of control, and moderate reductions in shoot dry weight.
**Cucurbitaceous crops.** Brushing of the cucurbit seedlings was initiated only at the cotyledonary stage. Brushing reduced stem elongation of 'Suyo Long' and 'Sweet Success' cucumber (Cucumis sativus) transplants 30% and 27%, respectively, and improved the plant appearance. Squash (Cucurbita pepo) was slightly less responsive to brushing: stem elongation of 'Dixie', 'All Seasons', and 'Cream of the Crop' was reduced 17%, 14%, and 25%, respectively. However, across squash cultivars, brushing reduced petiole length 43% and petiole dry weight 49%, without affecting leaf dry weight. Watermelon (Citrullus lanatus) cultivars vary in response to brushing, from no growth reduction for 'Sweet Favorite' to reductions of 45% in stem length and 24% in leaf area for 'Crimson Sweet'. Stem growth of 'Sugar Baby' watermelon was reduced 20% by brushing and plant appearance was improved.

**Cruciferous crops.** Broccoli and cabbage (Brassica oleracea) also show cultivar-specific responses to brushing, with two of five cultivars in each group exhibiting reductions in stem length after treatment. However, broccoli and cabbage seedlings were damaged by brushing, particularly when treatment was initiated at the second or third true-leaf stages. Stem length was generally reduced only 10 to 15% and some cultivars such as 'Conquest' exhibited excessive damage.

Brushing shows good potential as a non-chemical method of controlling the growth of some greenhouse-grown vegetable transplants, resulting in improved plant strength and appearance. Tomato and eggplant appear to be very responsive to the treatment, regardless of when brushing is initiated. Cucumber, watermelon and squash are responsive to brushing initiated at the cotyledonary stage, exhibiting moderate height control and very little leaf damage. In contrast, broccoli and cabbage did not respond well to brushing; exhibiting very little height control, but extensive damage on some cultivars, especially when treatment is initiated at later developmental stages. Brushing was least successful on pepper, which incurred moderate to extensive leaf damage depending on the experiment. In addition, Perhaps brushing is more injurious to plants with brittle leaves, such as pepper or cabbage. The application of other types of mechanical conditioning, such as shaking, vibration, or a static counterforce, may be less injurious to these more delicate transplants.

## Literature Cited

1. Latimer, J.G. 1991. Mechanical conditioning for control of growth and quality of vegetable transplants. HortScience 26:1456-1461.

2. Baden, S.A. and J.G. Latimer. 1992. An effective system for brushing vegetable transplants for height control. HortTechnology 2:412-414.
Mise au point d'un dispositif de mesure non destructif de la fermeté des fruits et des légumes. Essais sur tomate.

P. Lesage, M.-F. Destain

Mécanique agricole, Faculté des Sciences Agronomiques de Gembloux
2 Passage des Déportés, 5030 Gembloux (Belgique).

Introduction

Les consommateurs sont de plus en plus sensibles à la qualité des fruits et légumes dont ils se nourrissent. Cette notion de qualité apparaît de prime abord comme subjective. En fait, elle peut être mise en évidence à l'aide de divers tests chimiques (mesure de la matière sèche, des sucres, des acides, ...) ou physiques qui, le plus souvent, sont destructifs. Notre recherche s'apparente aux tests physiques et présente une méthode permettant de déterminer de façon non destructive la fermeté d'un fruit.

Principe de la méthode

La fermeté est la résistance offerte par le fruit ou le légume à la pénétration d'une tige. Habituellement, elle est mesurée de façon destructive à l'aide d'appareils du type Effigi ou Instron. Dans notre cas, la fermeté est mesurée en appliquant une force $F_1$ au fruit, à l'aide d'une tige qui se déplace de façon à provoquer une déformation élastique de la peau, selon la relation:

$$F_1 = \Delta x_f \times K_f \quad (1)$$

avec:

$\Delta x_f$ = déplacement de la tige dans le fruit (mm);

$K_f$ = raideur ou fermeté du fruit (N/mm).

La Figure 1 montre le principe du dispositif d'essai. La force $F_1$ provient du ressort à spirales AB, travaillant en traction et engendrant une force de rappel $F_2$. L'équilibre de la bascule répond à la relation générale suivante:

$$F_1 \times 70 = F_2 \times 30 \quad (2)$$

A partir de (1) et (2), on calcule la raideur du fruit selon:

$$\Delta x_r \times K_r \times 30 = \Delta x_f \times K_f \times 70 \quad (3)$$

avec:

$\Delta x_r$ = déplacement relatif mesuré des extrémités A et B du ressort (mm)

$K_r$ = raideur du ressort, mesurée au préalable (N/mm).

La méthode s'applique aux fruits ou aux légumes dont la fermeté de l'épiderme est inférieure ou égale à celle de la chair. L'essai est non destructif pour autant que le déplacement de l'extrémité de la tige de pénétration reste très faible. C'est là que réside la caractéristique principale du
dispositif d'essai: il est nécessaire d'obtenir une grande précision à la fois dans la réalisation du montage expérimental et dans la mesure des déplacements.

<figure><img src="image_122.png" /><figcaption>Fig. 1. Schéma de principe du dispositif de mesure de la fermeté</figcaption></figure>

$F_1$ = force exercée par le fruit;

$F_2$ = force de rappel du ressort.

<figure><img src="image_123.png" /><figcaption>Fig. 2. Evolution de la fermeté des tomates au cours du temps.</figcaption></figure>

## Essais sur tomates

Les essais ont été réalisés en imposant un déplacement maximum de la tige de pénétration dans le fruit égal à 1,5 mm. Dans cette gamme de mesures, le fruit n'est pas altéré et il existe une relation linéaire entre la force appliquée et la déformation de l'épiderme: la fermeté est donc constante.

Les tomates sont conservées à 4°C et les mesures sont répétées dans le temps, pendant une durée de 25 jours, ce qui permet d'observer l'évolution de leur fermeté. La Figure 2 montre les résultats obtenus pour un lot constitué de 30 tomates.

Bien que les tomates testées soient considérées par l'horticulteur comme "identiques", le coefficient de variabilité (C.V.) de leur fermeté atteint 17%.

La tomate n'est pas un fruit homogène, les mesures présentent un C.V. de 12 % selon que la mesure est effectuée sur une paroi carpellaire ou non.

Le résultat des mesures est faiblement affecté, quel que soit l'opérateur (C.V. de 7 %).

La comparaison des résultats obtenus en utilisant des méthodes de référence (INSTRON et EFFIGI), avec des tiges de 3 mm de diamètre, a permis de mettre en évidence des relations très hautement significatives et significatives, du point de vue statistique.

## Conclusions

- Sur tomate, tant que la profondeur de la tige reste inférieure à 1,5 mm, la déformation de l'épiderme reste élastique et il existe donc une relation linéaire force-déplacement qui permet de déterminer la raideur du fruit ou sa fermeté;

- Le test de mesure de fermeté proposé est non destructif;

- Le dispositif permet de mesurer l'évolution de la fermeté de tomates cueillies à un moment donné et stockées en chambre froide;

- L'intérêt majeur du test provient du fait que les mesures qu'il fournit sont corrélées avec celles issues des méthodes de référence habituellement utilisées sans être destructives.
APPAREIL DE MESURE DE LA RESISTANCE AU CASSAGE DE SCIONS D'ARBRES

J. LICHOU, A. AUDUBERT, M. EDIN
Ctifl
Centre de Balandran
B.P. 32
30127 BELLEGARDE
France

J.M. BROQUAIRE
SICA CENTREX
66440 TORREILLES
France

Le Ctifl et la SICA Centrex ont réalisé un prototype d'appareil destiné à mesurer la résistance à la rupture du point de greffe d'arbres fruitiers en vue d'avoir une appréciation précoce du niveau de compatibilité.

L'appareil permet de mesurer la force nécessaire au cassage avec une jauge de contrainte à lecture digitale. Un réglet permet de lire la longueur du déplacement pour fournir une information sur la flexibilité de l'union.

Des mesures seront effectuées en 1994 pour valider les données recueillies avec les notations réalisées sur vergers.

Cet appareil devrait pouvoir être utilisé pour des mesures de solidité et de fléxibilité du bois d'autres espèces d'arbres.

Selon la fiabilité des résultats et l'intérêt manifesté par les utilisateurs potentiels, une motorisation et une mémorisation automatique des données pourront être envisagées.
# The Sporangium as a Biomechanical Device.

Philip M. Lintilhac

The University of Vermont

Burlington VT, 05405, USA.

A central problem in plant developmental biology involves the differentiation of reproductive tissues. In contrast to animal development where the sexually competent germ line is differentiated and set aside early in embryology, in plants the sexual cells are produced from undifferentiated somatic cells which are genetically and phenotypically indistinguishable from any other undifferentiated cell. This means that genetic programming cannot be invoked as a first cause of reproductive differentiation. What biological mechanisms qualify as triggers of reproductive differentiation in plants?

In this paper I put forward the hypothesis that the sporangium, in all of its varied forms, is a stress mechanical device whose function is to shape and direct the mechanical forces produced by cell and organ growth, and that the differentiation of reproductive tissues is triggered by the unique stress mechanical conditions found at its center.

The multicellular sporangium is an ubiquitous plant structure. It is the characteristic reproductive structure for all plants from the bryophytes to the flowering plants where we find that the sporangium manifests itself in the integumented structure of the nucellus, which is the megasporangium, and in the anther sac which is the microsporangium.

Reproductive differentiation and development is initiated at a very early stage within the immature sporangium. In many cases a single cell is selected within a mass of identical cells. This means that some effector of great precision is able to reliably identify a single cell within a clonal mass and transmit a triggering signal to it alone.

Physically the sporangium is a container, usually roughly spherical or club-shaped, supported on a stalk of some sort. It usually comprises 1 or more concentric layers of cells which make up the sporangial wall, and an internal space or loculus within which differentiate reproductive structures such as spores, sperm cells, egg cells, or multicellular reproductive structures such as pollen grains, or the embryo sac. (Sinnott, 1960)

Developmental events within the sporangium lead inevitably to the production of reproductive cells, either by specialized mitoses as in the case of gametogenesis in the ferns, or more commonly by meioses which lead to the production of micro- and mega-spores in the higher plants. In the flowering plants meiosis within the mega- and micro-sporangia (the nucellus and the anther sac respectively) leads to the production of the embryo-sac and egg apparatus on the one hand and pollen grains on the other. These represent the full expression of the female and male gametophytes and result in the production of the egg and sperm cells respectively.

Traditional explanations for the differentiation of the reproductive cells invoke the establishment of steep chemical gradients which select centrally located cells for differentiation. However, the extreme precision necessary to locate single cells, and the temperature sensitivity of diffusion-based systems argue against gradient triggering mechanisms.

An alternative mechanism which relies only on the shape of the sporangium, and on locked-in stresses accumulated from cell enlargement growth, would seem to provide the necessary spatial precision, and freedom from environmental interference.

According to this hypothesis the outer layers of the sporangium accumulate compressive growth stresses due to successive anticlinal divisions and lateral expansion of the cells, however the free standing nature of the sporangium necessitates that it satisfies the conditions of an equilibrium structure, and that the circumferential compressive stresses present in the sporangial wall are balanced by tensile stresses distributed across the interior of the sporangium. (Lintilhac 1984)

In this way a cell or group of cells located at the center of the sporangium can be subject to unique mechanical conditions simply by virtue of their location and the build up of nat-
ural growth stresses within the structure. This would provide a temperature-independent, gra-
dient free, and potentially high precision mechanism for the initial induction of reproductive
differentiation.

The conditions which must be met for this mechanism to work are as follows: First, the sporangial head must be free-standing at the time of triggering, so that stresses generated in the sporangial wall equilibrate within the sporangium itself rather than being dissipated into surrounding structures which are touching it. Second, the mechanical coupling of the sporangial wall cells to the interior of the sporangium must be sufficient to effectively transmit tensile stresses to the cells at the center of the sporangium. Third, the constraints upon the shape of the sporangium are such that it must be roughly spherical or club shaped/cylindrical at the time of sporocyte differentiation so that the tensile forces secondarily induced in the central sporogenous region can be adequately focussed.

Evidence to support this hypothesis is at present restricted to a search for counter-examples reported in the literature. A survey of embryological and reproductive literature reveals *no* examples of cells of the outer sporangial wall differentiating into sporogenous cells. Secondly, in *every* case where the earliest stages of reproductive differentiation are adequately illustrated, it can be seen that the immature sporangium, however rudimentary, is a convex structure untouched by overlying tissues. Thirdly, sporangia are *always* club-shaped or nearly spherical during the initial stages of reproductive differentiation, and thus fulfill the requirements for a free-standing structure capable of focussing isotropic stresses on a central group of cells.

This interpretation of the sporangium as a stress-mechanical device solves the problem of reproductive differentiation in plants, and at the same time provides an unifying hypothesis which explains the homologies between sporangial structures from throughout the plant kingdom.

Examples of stress-mechanical controls during plant development are increasingly evident in the literature (Romberger, Hejnowicz, Hill 1993), (Lyndon 1990). What I propose here is that mechanical inputs into the developmental process offer the advantages of spatial precision and instantaneous action, and capitalize on the extensive apoplastic coupling of somatic cells. In this way mechanical effectors can meet the demands of developmental signalling in situations where hormonal signals cannot.

LITERATURE CITED

Lintilhac, P. M. 1984. Positional controls in meristem development: A caveat and an alternative. In *Positional controls in plant development*, Eds P. W. Barlow and D. J. Carr, 83-105. Cambridge University Press.

Lyndon, R. F. 1990. *Plant development: The cellular basis*. London: Unwin Hyman.

Romberger, J. A., Z. Hejnowicz, and J. F. Hill. 1993. *Plant structure: Function and development*. Springer-Verlag.

Sinnott, Edmund W. 1960. *Plant Morphogenesis*. New York: McGraw-Hill.
Continuous bending moment measurements from
gravitropically responding roots.

Philip M. Lintilhac, Sari Galanes and John Outwater
The University of Vermont,
Burlington, VT 05405 USA

Gravitropically stimulated corn roots growing in a humid environment respond to their horizontal orientation by growing downward. We have developed an experimental system for following the response by continuously monitoring the self-generated bending moments.

New instrumentation makes it possible to measure growth parameters previously inaccessible to measurement.

We place the roots between two horizontal teflon surfaces which act to restrain downward bending. The forces generated in the vertical direction are measured continuously with a Vitrodyne V-200 mechanical testing frame, acting in displacement controlled mode to prevent bending of the root. The self-generated load is measured as a restoring force necessary to maintain constant displacement between the two teflon surfaces as the bending root tries to force them apart.

Initial characterization of the system shows a pH dependence of the response, as well as a characteristic lengthening of the presentation time under high Calcium conditions, and a depression of the bending moment output when the roots are flooded with 10⁻³ M EGTA. Decapping also eliminates all bending force production by the root.

Other measurements made possible by this system include axial growth rate measurements under continuous controlled tip load, indicating the sensitivity of overall root growth rates to tip impedance.

These measurements may afford a more realistic means of following the gravitropic bending response since they more accurately mimic the conditions existing in soil where the root is acting against a resistance (Goss, Russell 1980), (Goss 1977), (Feldman 1984). Using these methods we hope to build a more realistic biomechanical model of root performance.

LITERATURE CITED

Feldman, Lewis J. 1984. Regulation of root development. *Ann. Rev. Plant Physiol.* 35:223-42.

Goss, M. J. 1977. Effects of mechanical impedance on root growth in barley. *Jnl. Exp. Bot.* 28:96-111.

Goss, M. J., and R. Scott Russell. 1980. Effects of mechanical impedance on root growth in barley, (Hordeum vulgare L.). *Jnl. Exp. Bot.* 31:577-88.
# Changes in wall architecture during plant cell growth and differentiation

Maureen C. McCann and Keith Roberts

Department of Cell Biology, John Innes Institute, Colney Lane, Norwich NR4 7UH, UK.

The macroscopic properties of fruits, vegetables, cereal crops, and plant-derived materials of industrial importance such as wood, paper and cotton, derive from the properties of plant cells and their surrounding walls (1). The biomechanical properties of each tissue within a plant are functions of the tissue anatomy (that is, cell shape, size, and packing), the adhesion between neighbouring cells, and the thickness and material composition of the cell walls. Cell walls form an apoplastic continuum in which the cells are compartmentalised constraining cell size and shape. Cell-cell adhesion depends upon the architecture of the regions of interface between walls from neighbouring cells, the middle lamella and cell corners. For example, mesophyll cells have reduced cell-cell adhesion to generate air-spaces. Even very minor changes in sugar composition, such as the absence of sucrose, can have profound consequences for the tensile strength of cell walls (2). However, very little is known about the basic architecture of cell walls, and the changes in that architecture that occur during growth and differentiation, features that underpin the mechanical and rheological properties of whole tissues and plants (3, 4).

Our use of many methodologies has demonstrated that the apoplastic continuum is a mosaic of different architectures with major architectural differences between species, between tissues, and between domains within a single wall. In addition to conventional electron microscopy techniques, sugar analysis, FT-Raman spectroscopy and NMR spectroscopy, we have applied several novel methodologies which are suitable for analysis at the single cell wall level, including cryopreservation techniques for electron microscopy (5), the generation of probes to particular cell wall epitopes (6), and Fourier Transform Infrared microspectroscopy (7). The fast-freeze, deep-etch, rotary-shadowed replica technique allows us to visualise cell wall architecture at high resolution, as close to the in vivo state as possible, and with preservation of the three-dimensional spatial relationships of polymers. Images obtained by this method allowed us to propose a model of cell wall architecture for one chemically simple system, onion parenchyma cells (4), based on two inter-penetrating and coextensive networks, a load-bearing cellulose/xyloglucan network and a pectic network that, whilst not load-bearing, may nevertheless control the access and activity of enzymes that act on the cellulose/xyloglucan network by limiting wall porosity. Fourier Transform Infrared (FTIR) microspectroscopy permits us to detect the presence of some specific chemical bonds within the wall, and, in combination with polarisers, to detect their orientation. FTIR spectra constitute species-specific and tissue-specific fingerprints of cell walls, reflecting even subtle differences in composition. By generating a large spectral database, we hope eventually to use statistical analysis packages to correlate specific spectral features with particular cell wall properties such as tensile strength, and to establish predictive models.

Bearing in mind the spatial diversity of architectures, which may then confer differential mechanical properties on different organs of the plant, and within those organs on different parts of the wall, we have chosen to look at changes in wall architecture in suspension-cultured cells, since these are relatively homogeneous and easily manipulated in culture. We have mapped changes in composition and architecture of matrix polymers in carrot (8) and tobacco (9) suspension cultures during cell elongation, and Zinnia mesophyll cells during differentiation to tracheary elements at the single cell wall level. We observe changes in both the cellulose/xyloglucan network and the pectic network. In elongating cells, orientation of matrix polymers in addition to cellulose microfibrils
transverse to the long axis of the cell occurs. The original pectic network may be replaced by a
more highly esterified network with altered rheological properties. Some constraints operate; wall
thickness and microfibril spacing are maintained. In differentiating cells, new varieties of cell wall
polymer are produced in a developmentally-regulated manner. Our observations lead us to propose
some tentative models for the molecular rearrangements that occur within these walls during
growth and differentiation. The biomechanical properties of plant tissues will depend on both the
geography and history of the component cells and their walls.

1. McCann, M.C. and Roberts, K. (1993) Plant cell walls: murals and mosaics. Agro-Industry Hi-Tech, in press.

2. Reiter, W.D., Chapple, C.C.S., Somerville, C.R. (1993). Altered growth and cell-walls in a sucrose-deficient mutant of Arabidopsis. Science 261, 1032-1035.

3. Carpita, N.C. and Gibeaut, D.M. (1993) Structural models of primary cell walls in flowering plants: consistency of molecular structure with the physical properties of the walls during growth. The Plant Journal 3, 1-30.

4. McCann, M.C. and Roberts, K. (1991) Architecture of the primary cell wall. In The Cytoskeletal basis of plant growth and form (ed. C.W. Lloyd), pp 109-129. Academic Press, London.

5. McCann, M.C., Wells, B. and Roberts, K. (1990) Direct visualisation of cross-links in the primary plant cell wall. J. Cell Sci. 96, 323-334.

6. McCann, M.C., Wells, B. and Roberts, K. (1992) Complexity in the spatial localisation and length distribution of plant cell-wall matrix polysaccharides. J. Microscopy 166, 123-136.

7. McCann, M.C., Hammouri, M.K., Wilson, R.H., Belton, P.S. and Roberts, K. (1992) Fourier Transform Infra-Red microspectroscopy is a new way to look at plant cell walls. Plant Physiology 100, 1940-1947.

8. McCann, M.C., Stacey, N.J., Wilson, R.H. and Roberts, K. (1993) Orientation of macromolecules in the walls of elongating carrot cells. J. Cell Sci. 106, 1347-1356.

9. McCann, M.C., Shi, J., Roberts, K. and Carpita, N.C. (1994) Changes in pectin structure and localisation during the growth of unadapted and NaCl-adapted tobacco cells. The Plant Journal, in press.
Cellular basis of tissue strength in carrots

A McGarry

Horticulture Research International

Wellesbourne

Warwick CV35 9EF

UK

Carrots (Daucus carota) are subject to two major forms of damage, splitting (longitudinal cracking) and (transverse) breakage. Whilst breakage is largely a man-made problem caused by deficiencies in handling procedures, splitting can occur without human intervention. It must, therefore, be a consequence of carrot growth and development.

Some earlier work at HRI demonstrated that carrots split by cell wall breakage, even when cell packing appears to be structurally unsound. For instance, in the cultivar Tamino groups of cells are aligned with their walls in the same longitudinal plane. Despite this fracture is intracellular. As a result, the toughness of carrot tissue must be largely determined by cell wall strength.

Whilst splitting has been the subject of several empirical studies, the literature contains few clues to the causes of splitting or the basis of tissue strength in carrots. However, since variety trials indicate that certain cultivars consistently produce large numbers of split roots there would appear to be a genetic influence. Work on other horticultural products has shown that susceptibility to damage increases with turgor pressure. For these reasons work at Wellesbourne has concentrated on examining the cellular basis of tissue strength in carrots as affected by water status, genotype and agronomy.

Recent work has shown that,

(i) the fracture toughness (as measured using a crack-opening test) of phloem parenchyma tissue is negatively correlated with turgor,

(ii) tissue strength (as measured using a tensile test) is virtually independent of turgor but related to tissue apoplast volume (a measure of cell wall volume fraction),

(iii) carrot tissue is notch-sensitive. The introduction of a notch weakens a test piece out of proportion with the amount of material removed by notching. As turgor increases, carrot tissue becomes more notch-sensitive as the notch tip becomes more defined and more effective as a stress concentrator,

(iv) altering the timing of irrigation (but not the total amount) can produce carrots with different mechanical properties. Heavy irrigation during the period 56 - 90 d after drilling not only produces a large number of growth split roots (ca. 20%), but tougher tissue. This increase in toughness cannot be fully explained by differences in root water status.
# Problèmes mécaniques inhérents au mouvement révolutif d'exploration des tiges volubiles

B. Millet, B. Bonnet et P.M. Badot

Laboratoire de Sciences végétales, Université de Franche-Comté, Place Leclerc, 25030 Besançon Cedex (France)

Les plantes grimpantes sont connues pour leur aptitude à enrouler leur tige autour d'un tuteur (ex. : le haricot à rame) et à s'élever ainsi à plusieurs mètres au-dessus du sol. Ce mouvement d'enroulement est précédé par un mouvement d'un autre type le mouvement révolutif d'exploration au cours duquel l'extrémité de la tige décrit plusieurs cercles avant de rencontrer un support.

Les observations effectuées sur un nombre imposant d'espèces, ont conduit à dégager quelques règles concernant les caractéristiques du mouvement révolutif d'exploration : l'extrémité des tiges volubiles manifeste une courbure allant jusqu'à 90 degrés avec la partie proximale, le sens du mouvement est fixé génétiquement (la tige du Houblon tourne dans le sens des aiguilles d'une montre, celle du Haricot en sens inverse), la trajectoire est inclinée par rapport à l'horizontale, le mouvement est associé à l'élongation de la tige.

Des mesures à intervalles de temps rapprochés (5 ou 10 minutes) pendant plusieurs heures permettent de reconstituer la trajectoire décrite par l'extrémité de la tige au cours de sa croissance (fig. 1), de calculer la période du mouvement, son amplitude, sa vitesse et de suivre les variations de la hauteur du bourgeon terminal au cours d'une révolution (fig. 2).

Les éléments d'information rassemblés sont utiles pour tenter de construire une hypothèse explicative. Le fait que la durée de la période soit dépendante de la température, par exemple, est à prendre en considération. Concernant la mécanique du mouvement elle-même, trois questions se posent :

1/ Pourquoi la période du mouvement est-elle plus courte lorsque la portion libre de la tige est immobilisée à 20 cm du sommet que lorsqu'elle est longue de 10 cm ?
2/ La base de la tige peut être considérée comme étant fixe. Si on assimile la tige à un cylindre allongé de faible diamètre immobilisé par sa base, la partie apicale ne peut tourner que si des déformations apparaissent au niveau de la zone courbée. Comment expliquer mécaniquement la rotation de la tige sans torsion ? Au cours d'une révolution en effet, la même cellule se dilate et se contracte alternativement sous l'influence des variations de pression de turgescence dont elle est l'objet. Le phénomène se répète pendant le temps durant lequel cette cellule se trouve dans la zone de courbure, c'est-à-dire pendant une dizaine de révolutions

3/ Le mouvement révolutif d'une tige ne peut pas être assimilé à un mouvement circulaire uniforme car la vitesse de déplacement passe par un maximum et un minimum au cours d'une révolution. C'est lorsque la tige est sur le point de culminer que sa vitesse est la plus grande et lorsqu'elle se trouve à sa position la plus basse que la vitesse est la plus lente.

Les problèmes mécaniques se compliquent lorsqu'on s'adresse aux vrilles ou au mouvement d'enroulement des tiges autour du tuteur. Quoi qu'il en soit, les réponses apportées à ces questions par les mécaniciens seront intéressantes à prendre en considération pour comprendre les processus physiologiques à l'échelle cellulaire.

<figure><img src="image_124.png" /><figcaption>Fig. 1. Extrémité d'une tige de Haricot grimpant. 1. Partie linéaire horizontale. 2. Zone de courbure. 3. Partie linéaire verticale.</figcaption></figure>

<caption>Fig. 2. Mouvement révolutif de la tige de Haricot. a) Projection sur un plan horizontal de la trajectoire décrite par l'extrémité d'une tige de Haricot. Le point ω correspond à la projection sur le plan du point d'immobilisation de la tige. Les nombres de 1 à 53 permettent de suivre la trajectoire. Les points successifs sont portés toutes les 10 min. b) En pointillés, les variations au cours du temps de la distance de l'extrémité de la tige par rapport au plan horizontal passant par le point d'immobilisation (cote de hauteur). En trait plein, les variations correspondantes de la vitesse de déplacement de l'apex, exprimées en mm/10 min (Millet et coll., 1984).</caption>
# Biomechanics and the evolution of plant form

## Volker Mosbrugger, Tübingen

Due to numerous morphological studies of fossil and Recent plants, the evolution of plant forms from unicellular to multicellular algae and finally to the various land plants is relatively well known. With respect to growth forms and structure, all algae remain comparatively simple whereas land plants developed a variety of highly complex plant forms. The earliest land plants from the Upper Silurian to Early Devonian (about 420 to 380 million years ago) consist either of simple flat-lying leaf-like structures or of dichotomously branched and naked upright axes (Fig. 1). At least the larger upright axes of more than a few millimeters in height have a cuticle, stomata and a central protostelar vascular bundle. From these simple early land plants more complex plant forms evolved: branching patterns became increasingly irregular and the vascular bundles more complex (Fig. 2); cambial growth and leaves with successively more intricate venation patterns developed. By the Carboniferous (about 350 to 300 Million years ago), land plants attained the basic structural complexity and life forms of modern land plants such as herbs, shrubs, trees, and lianas.

Four stages in the evolution of plant forms are analyzed using a biomechanical approach (including fluid dynamics): 1. evolution of morphologically complex algae; 2. evolution of growth forms and branching patterns in early land plants (cf. Fig. 1); 3. evolution of complex stelar types (cf. Fig. 2); 4. evolution of leaves and leaf venation patterns. The analysis of these examples indicates that size is the crucial driving force of the evolutionary sequence. For land plants an increase in size may be advantageous for various reasons (i.e. competition and light interception, reproduction, dispersal, etc.). It, however, also entails a number of difficulties because the surface to volume ratio (and hence photosynthesis and transpiration), stability and transport requirements for water and nutrients are size dependent. The evolution of more complex plant forms can therefore be understood in terms of an optimization process in which plants tend to develop an "optimum compromise" in which stability, a high photosynthetic surface and an internal water balance is maintained despite an increase in size.

At least parts of the morphological and anatomical changes of this evolutionary sequence resemble a self-organization process governed by the size increase. This is particularly evident in the evolution of the vascular system of shoot axes. For instance, FE-simulations of the water transport efficiency of various primitive bundle types indicate that an increasing axis diameter requires a more peripheral arrangement of the vascular system thus also leading to a higher second moment of area of the xylem. Obviously, this marks the beginning of a functional shift in the evolution of the xylem: although the vascular system evolved as a water transport device, it then became a compromise structure providing water transport and bending stiffness.

All the examples discussed illustrate that plant biomechanics is essential if a causal understanding of plant evolution is to be achieved.
<figure><img src="image_125.png" /><figcaption>Fig. 1: Growth habits of some early land plants (adapted from various authors). a. Rhynia b. Aglaophyton c. Cooksonia d. Sciadophyton e. Spongiphyton f. Protosalvinia g. Parka</figcaption></figure>

<figure><img src="image_126.png" /><figcaption>Fig. 2: Some basic stele types realized in tracheophytes</figcaption></figure>
The effect of gibberellin on weeping of growing branches of the Japanese
cherry, *Prunus spachiana*

Teruko Nakamura¹, Maki Saotome¹, Tamiko Yamazaki¹, Kei'ichi Baba²,
Takao Itoh² and Toshitaka Yokoyama³

¹Laboratory of Plant Physiology, Faculty of Science, Japan Women's
University, Bunkyo-ku, Tokyo 112, Japan

²Wood Research Institute, Kyoto University, Uji, Kyoto 611, Japan

³Tama Forest Science Garden, Forestry and Forest Products Research
Institute, Hachioji-shi, Tokyo 193, Japan

There have been very few studies of the weeping of growing shoots
in woody plants. So, we have investigated the weeping using current-year
branches of grafts of the Japanese cherry, a weeping type of *Prunus
spachiana* and obtained the following results. 1, Current-year branches
first elongate upward then gradually bend to elongate downward. The
weeping growth may not be differential growth. 2, Gibberellin (GA<sub>3</sub>)
applied to apical buds 4 times weekly promoted the upward elongation of
the branches and inhibited their bending. Namely GA<sub>3</sub> changed the
orientation of branches during their growth. 3, The results on xylem
thickening, vessel density and cellulose microfibril angle may suggest that
the tension wood appears to be formed at the basal part of the branches
treated with GA<sub>3</sub>. In control branches, no tension wood was formed.

4, GA₄ did not show any effect on the orientation of the branches.

5, The similar effects of GA₃ were obtained using *Prunus persica* of
weeping type. 6, These results suggest that the weeping habit may be caused by the lack of mechanical rigidity due to the failure of a hormonal-control system relating to gibberellin.

<figure><img src="image_127.png" /><figcaption>1</figcaption></figure>

<figure><img src="image_128.png" /><figcaption>3</figcaption></figure>

<figure><img src="image_129.png" /><figcaption>4</figcaption></figure>

<figure><img src="image_130.png" /><figcaption>2</figcaption></figure>

<figure><img src="image_131.png" /><figcaption>5</figcaption></figure>

Photographs showing the effects of GA₃ and GA₄ in the current year branch of *Prunus spachiana* of weeping type (1-4) and the branch of upright type (5) which is shown to be compared with the result shown in weeping type.

GA treatment was done 4 times every week. Photograph was taken 7 days after the last treatment.

1: Control, 2: 10 µg/plant GA₃, 3: 10 µg/plant GA₄, 4: 100 µg/plant GA₄.

Arrow: vertical direction, Bar: 50 mm
# Internal stresses due to growth and differentiation in Norway Spruce

- measurements and results

Magnus Nilsson, Department of Structural Engineering,
Lund University, P.O. Box 118, S-221 00 Lund, Sweden

## Introduction

In a research project, established in 1993, the presence, distribution and extent of the internal stresses in Swedish softwood are to be determined. A rather comprehensive programme will be carried out, including measurements of internal strains, variation of the modulus of elasticity in green timber and different parameters significant influence on the internal stresses. To achieve this, methods for measuring the internal strains in longitudinal, radial and tangential directions are developed. The first face of the investigation deals with the internal stresses in full grown Norway spruce (Picea Abais) from different types of site quality.

## Method

Based on methods presented by Jacobs (Bulletin Commonwealth Forestry Bureau, 1945) and Post et. al. (Wood Science and Technology 14, 1980), a method is developed to measure the internal strains in logs. In longitudinal direction the distance between well-defined points is measured, with a resolution of 10 µm, before and after cutting the log in strips with a cross-section of 50x50 mm² and a length of 1000 mm. The cutting is done using a frame saw, thereby achieving a fast processing in order to maintain the green condition. The MOE is determined immediately after cutting, using a simplified bending test, which is related to more careful investigations done in the laboratory. In tangential and radial direction are the internal strains measured in the same manner, but here using smaller strips of 50x50x30 mm³.

## Measurements

In three different sites, located within the same area, with site quality varying from poor to fairly good, sample areas of about 2.500 m² are selected. The history of the sites is quite known. In these areas are height, diameter breast height and type of crown determined for each tree, as well as their position. The trees are classified, and 13 trees are selected from each site representing different quality classes. After felling, these trees are investigated more carefully, parameters like type of bark, distribution and form of knots and occurrence of defects are determined.
The marking of cross-cutting is done so that three logs, each of a length of three meter, are cut from root-, middle- and top-log. In these logs internal strain and MOE in compression respectively tension are determined in longitudinal, radial and tangential direction.

Measurements are also done in order to determine quite a few wood properties, i.e. density, moisture content, magnitude of growth rings, length and width of fibres and micro-fibril angle.

Logs not used in the determination of parameters described above, are processed to sawn timber and kiln dried using common techniques. The timber that is produced from these logs is stress graded and classified according to Swedish standards, and the defects are measured.

The expected results from the investigation, can be related to three levels. The influence on the presence, distribution and extent of the internal stresses related to the site quality, the type of tree in a site and finally within the tree itself are to be determined. By searching correlation between parameters describing the site, the tree respectively the wood and the internal stresses, the influence of such parameters on the internal stresses can be determined.
# Biomechanical Control of Elongation Growth by Phytohormones and Osmotic Stress

Hisashi Okamoto and Akane Okamoto

Graduate School of Integrated Science, Yokohama City University
22-2, Seto, Kanazawa-ku, Yokohama, 236 Japan

Elongation growth of plant cell or stem in a steady state can be described by the Lockhart's simultaneous equations:

$$v = (1/V)(dV/dt) = \Phi(P - Y) \quad (1)$$

$$v = (1/V)(dV/dt) = L(\Delta\pi - P) \quad (2)$$

Eq. (1) is the mechanical equation of empirical nature representing the cell wall yielding, where V is the volume, Φ is the extensibility of the cell wall, P is the turgor and Y is the yield threshold of the wall. Eq. (2) is the (irreversible) thermodynamic equation of water uptake, where L is the relative hydraulic conductivity of the plasmalemma and Δπ is the osmotic pressure difference across cell membrane.

From the biomechanical point of view, it is quite pertinent for the understanding of the mechanism of growth control to analyze the effects of phytohormones or osmotic stress on the elongation growth in terms of the changes in the biophysical parameters involved in both equations, although it is not easy to determine all of them simultaneously. Since the work done by Green and Cummins (1974), Cleland (1977) and Cosgrove (1985), it has generally been believed that auxin (IAA) increase Φ to elevate v, but has no effect on Y. It is well established that P is kept constant during growth promotion by IAA (Nakahori et al. 1991).

However, by means of the pressure jump methods, both positive (Okamoto et al. 1989) and negative (Okamoto et al. 1990), in combination with the continuous pressure probe measurement (Nakahori et al. 1991), it has been discovered that *Y* *in vivo* is decreased largely by the action of IAA (by 40-100 kPa), or more with the adaptation to osmotic stress.

It is quite clear now why the regulatory change in Y in higher plants due to hormonal action had not been discovered until rapid pressure jump method was invented recently. Applying a small jump in xylem pressure (10 kPa x 2 min), turgor P lifts up by ΔP owing to the increase of water influx. According to the eq. (1), the steady growth rate will increase from v₁ to v₂.

Thus we can estimate wall extensibility and effective turgor as follows:

$$\Phi = (v_2 - v_1) / \Delta P,$$

$$P - Y = v_1 / \Phi$$

The classic methods, osmotic equilibrium (Green & Cummins 1974, Cleland 1977) or stress relaxation (Cosgrove 1985), used too big changes in turgor (more than 50-100 kPa) and/or required too long time (1-3 h) to obtain a single Y value. Regulatory mechanism to keep the growth rate constant was activated under such circumstances and Y had been decreased by and by to a minimum value, say 0.3 MPa (Cosgrove 1985) or so, until the determination was over.

In order to investigate whether the yield threshold still exists in an *in vitro* system, we prepared glycerinated hollow cylinder (GHC) from cowpea hypocotyl. An extensometer has been developed to enable perfusion of experimental solution through the hollow and infusion of the solution into the tissue without abrasion of the cuticle layer on the organ surface. Stress-strain experiments clearly showed the existence of the pH-dependent yield threshold (y) in this *in vitro* system too. Acidification of the perfusion solution, from pH 6.2 to pH 4.0, caused the reversible decrease of y by 55 g/ GHC, which coincides with the decrease of *Y* *in vivo* by ca.
70 kPa (56 g/segment) due to IAA action (Fig. 1 (a)). These results strongly support the "acid growth theory" since it has already been established in cowpea that the proton pumps are activated by IAA *in vivo* prior to growth promotion (reviewed in Katou & Okamoto 1992), and the apoplast in the elongation zone of intact hypocotyl is acidified to pH 4 under natural condition (Katou & Okamoto 1970).

Heat treatment of the GHC completely inhibits the decrease of y with acidification (Fig. 1 (b)). Increase of φ (*in vitro*) by acidification is not completely inhibited until being treated with a higher temperature. These discoveries suggest the participation of certain functional proteins (enzymes?) that reduces the activation energy of net splitting of weak bonds between cellulose microfibrils and hemicellulose bridges (corresponding to y), and that of sliding of the hemicellulose tethers along cellulose microfibrils (corresponding to φ).

<figure><img src="image_132.png" /><figcaption>Fig. 1</figcaption></figure>

The results of the
stress-strain experiments
*in vitro*

The stress-strain relationship
can be exactly simulated by
Lockhart mechanical equation
with pH-dependent yield
threshold (y).

The glycerinated hollow
cylinders, 15 mm in length,
were prepared from cowpea
hypocotyl segements excised
from the elongation zone.
They were stocked in 50 %
glycerol aqueous solution for
3 weeks under -15°C. The
extension rates were
determined under various
tensions during 10 - 30 min
after changing the load. The
reaction pH was controlled by
perfusion of buffer solution of
the 10 mM acetate(pH 4) or
10 mM histidine (pH 6)
through the hollow. The heat
treatment was 90°C x 1 min in
50 % glycerol solution.

References

Katou, K. & Okamoto, H. (1992) Intern. Rev. Cytol. 142 (263-304).

Nakahori, K. et al. (1991) Plant Cell Physiol. 32 (121-129).

Okamoto, H. et al. (1990) ibid. 31 (783-788).

Okamoto, H. et al. (1989) ibid. 30 (979-985).

Cosgrove, D. (1985) Plant Physiol. 78 (347-356).

Cleland, R. (1977) Symp. Soc. Exp. Biol. 31 (101-115).

Green, P. B. & Cummins, W. R. (1974) Plant Physiol. 54 (863-869).

Katou, K. & Okamoto, H. (1970) Plant Cell Physiol. 11 (385-402).
# How to determine the Biomechanical Growth Parameters *in vivo* and *in vitro*?-----A Theoretical and Technical note.

Akane Okamoto, Kiyoshi Katou* and Hisashi Okamoto

Graduate School of Integrated Science, Yokohama City University
22-2, Seto, Kanazawa-ku, Yokohama, 236 Japan and *Graduate School of Human and
Information Science, Nagoya University, Furo-cho 1, Chikusa-ku, Nagoya, 460-01 Japan

## I. Lockhart's Simultaneous Growth Equations and Katou's Diagram

The steady growth rate of plant cell or organ is described by Lockhart simultaneous equations:

$$v = (1/V)(dV/dt) = \Phi(P - Y) \quad (1)$$

$$v = (1/V)(dV/dt) = L(\Delta\pi - P) \quad (2)$$

$v$, relative growth rate; $V$, the volume; $\Phi$, the wall extensibility; $P$, intracellular hydrostatic pressure; $Y$, yield threshold; $L$, relative hydraulic conductance; $\Delta\pi$, osmotic pressure difference across membrane. Eq(1) is a mechanical equation of the cell wall yielding and Eq. (2) is the thermodynamic equation of water uptake. Both process must occur simultaneously.

In this equation, $P$ seems to play a contradictory role: it behaves as if it were a promoter of growth in Eq. (1) since it is a driving force of cell wall yielding, and as if it were an inhibitor of growth in Eq. (2) since it is an opponent against water uptake.

This contradiction was theoretically solved by Katou (1986) as illustrated in Fig. 1. We call the crossing point of the two lines which represent Eq. (1) and (2) "operational point" of the growth mechanism whose position is determined by two parameters ($P$, $v$).

## II. Determination of the Cell Wall Extensibility ($\Phi$) and the Yield Threshold of Cell Wall (Y) *in vivo* by pressure Jump Methods.

As shown by a bold triangle in Fig. 1, we can lift up turgor by $\Delta P$ by applying a jump in the xylem pressure ($P_x$) of a stem segment by means of the xylem perfusion system (Okamoto et al. 1989), since water influx from the xylem vessel is enhanced. After about 30 s, the transient elastic extension is relaxed. The steady growth rate increases from $v_1$ to $v_2$. Then we can determine the wall extensibility as follows:

$$\Phi = (v_2 - v_1) / \Delta P$$

Simultaneously, we can determine the effective turgor:

$$P - Y = v_1 / \Phi$$

An example of the positive pressure jump is shown in Fig. 2.

In order to determine more precisely the yield threshold $Y$, negative pressure jump method was devised (Okamoto et al. 1990) in combination with the determination of $P$ by a pressure probe (Nakahori et al. 1991). Instead of a positive pressure, short pulses (2 min) of negative pressure are applied to the xylem vessel until the growth is halted. A typical example is shown
in Fig. 3, where the P<sup>K</sup> axis can be converted to P axis irrelevantly whether IAA is perfused or not, since it was proved that IAA does not change P during growth promotion (Nakahori et al. 1991). IAA definitely decreases Y by 80 kPa and accelerates elongation of cowpea hypocotyl segment (Fig. 3 and Nakahori et al. 1991).

### III. Determination of the wall extensibility (Φ) and the Yield Threshold Tension (y) in vitro: Glycerinated Hollow Cylinder System

Glycerinated hollow cylinders are prepared by boring the elongation region of cowpea hypocotyl with a stainless steel cylinders of sharp edge. They are immersed in 50 % glycerol aqueous solution at -15 C for 2-3 weeks. Abrasion of the cuticle layer on the epidermal surface is not necessary since any experimental solution can be perfused through the hollow in an extensometer of novel design. The stress-strain experiment is reported in another paper (p. -p. ) and elsewhere (Okamoto & Okamoto 1994).

<figure><img src="image_133.png" /><figcaption>Fig. 2</figcaption></figure>

<figure><img src="image_134.png" /><figcaption>Fig. 3</figcaption></figure>

<figure><img src="image_135.png" /></figure>

### References

* Katou, K. & Furumoto, H. (1986) Protoplasma 133, (174-185)

* Nakahori, K., Katou, K., & Okamoto, H. (1991) Plant Cell Physiol. 32 (121-129)

* Okamoto, H., Liu, Q., Nakahori, K. and Katou, K. (1989) ibid. 30 (979-985)

* Okamoto, H., Miwa, C., Masuda, T., Nakahori, K. & Katou, K. (1990) ibid. 31 (783-788)

* Okamoto, H. & Okamoto, A. (1994) Plant Cell Environ. (in Press)
# A Physical Behavior of Tree During Secondary Growth

- Diurnal change of tangential strain of sapling -

T.Okuyama, M.Yoshida, H.Yamamoto and T.Sakai

School of Agricultural Sciences

Nagoya University, Nagoya, 464-01 Japan

Diurnal change of inner bark strain which was induced by turgor pressure in the phloem was measured according to the strain gage method (Fig.1). Used materials were 3-year-age saplings of kuromatsu (Pinus thunbergii Parl.) and sugi (Cryptomeria japonica D.Don).

Strain gage printed on a plastic film with water proof cover was used with one active gage and three wires connection method. Arranging two or three measuring positions on the stem of each sapling, removing carefully the outer bark, strain gage with 4 mm in the length was pasted on the tangential direction of the surface of the inner bark. The strain gage was put over with vaseline and aluminum foil to protect from direct illumination and shrinkage. Strain change was also measured on the surface of an Invar rod to cancel the temperature drift of strain measurement devices. Strain output became stable within half hours after putting the strain gage and the strain drift by temperature was less than ±5μ strain / °C. Then the total measuring error during the experiment was estimated less than ±20μ strain including divers factors after the correction of temperature effect.

Measurement was carried out in the following three conditions.

1. In a room condition without any climate controls.

2. In a phytotron with natural sunlight, constant conditions at the temperature of 25°C and 60% of humidity.

3. In a growth cabinet at the temperature of 20°C, 90% of humidity and light control.

The results are as follows.

1. Strain change in the tangential direction of phloem is about ten times as large as that of xylem. Then the strain change comes from the change of turgor pressure in the phloem cells.

2. The minimum tangential strain, the maximum shrinkage, appears at about 14 o'clock in the natural climate condition, the strain increases (expands) gradually from afternoon to night, then reaches the maximum value at just before daybreak. The decrease in the strain (shrinkage) occurs sensitive to the light illumination. However the rate of decrease in the strain is faster than the increase after putting out the illumination, then a clear hysteresis can be seen in the periodic change of strain.

The strain change shows cyclic ups and downs corresponding to the sunlight period. It follows faithfully to the various lightening periods even under the light controlling condition (Fig.2).

3. A phase difference could not be observed between tangential strains in the various height in a sapling. This result predicts that the water in the phloem cells comes from the xylem according to the pressure difference between xylem and phloem cells.

4. The minimum strain during lighting period recovers rapidly to the maximum strain soon after the topping. The strain recovery according to topping shows faster movement than that at putting out the light (Fig.3,4).

5. The maximum shrinkage is in proportion to the logarithm of intensity of illumination. The amount of turgor pressure estimated from the change of the tangential strain was 10-50 KPa.

The tangential strain on the surface of inner bark gives a diametral change induced by turgor pressure change with enough accuracy. This method can be used for discussion on the role of water stress in the secondary growth of tree.
<figure><img src="image_136.png" /><figcaption>Fig.2 The course of the strain of a sapling</figcaption></figure>

<figure><img src="image_137.png" /><figcaption>Fig.3 The effect of topping on the strain</figcaption></figure>

<figure><img src="image_138.png" /><figcaption>Fig.4 Course of strain after three kinds of treatment</figcaption></figure>

<figure><img src="image_139.png" /></figure>
# Plant and Fungal Cell Growth: Governing Equations for Cell Wall Extension and Water Transport

Joseph K. E. Ortega

Professor of Mechanical Engineering and
Director of the Bioengineering Laboratory
Department of Mechanical Engineering
University of Colorado at Denver
Campus Box 112, P.O. Box 173364
Denver, Colorado 80217-3364, USA

## Summary

Plant and fungal cell growth (enlargement) is a result of many complex biochemical and metabolic events in combination with physical processes. During the past decade, progress has been made in the development of "governing equations" that describe the relevant physical processes in terms of biophysical and biomechanical parameters. The magnitude and behavior of these parameters are controlled by biochemical and metabolic events.

Historically, governing equations play a key role in the evolution of a science from a descriptive, or qualitative, state to a quantitative state. It is well known that governing equations are fundamental to the physical sciences. For example, the field of electricity and magnetism would be severely diminished without Maxwell's Equations, and the fields of fluid mechanics and convective heat transfer would be reduced to an empirical science without Navier-Stokes Equations. Physical scientists and engineers have come to rely on the use of governing equations to determine the magnitude and behavior of a "parameter of interest" when several other parameters change simultaneously.

This communication will review recent progress made toward the goal of establishing governing equations for the two interrelated and simultaneous physical processes that are involved in plant and fungal cell growth; the rate of cell wall extension and the net rate of water uptake. The Augmented Growth Equations (1, 2, 3, 4; see References) provide the foundation for governing equations. The first Augmented Growth Equation describes the rate of cell wall extension and may be formulated to account for both irreversible (plastic) and reversible (elastic) extension. This equation relates the relative rate of change in volume of the cell wall chamber, $v_c$, to the sum of the relative rate of irreversible (plastic) extension and the relative rate of reversible (elastic) extension (1, 2, 3, 4):

$$ [1] \qquad v_c = (dV_c/dt)/V_c = \phi(P-Y) + (dP/dt)/\epsilon, $$

where $V_c$ is the volume of the cell wall chamber, $t$ is the time, $\phi$ is the relative irreversible wall extensibility, $P$ is the turgor pressure (the pressure difference between the cell interior and the external medium), $Y$ is the yield threshold (a magnitude of turgor pressure which must be exceeded before plastic wall extension occurs) and $\epsilon$ is the volumetric elastic modulus. The term, $\phi(P-Y)$, represents the relative rate of plastic, or permanent, wall extension. The term, $(dP/dt)/\epsilon$, represents the relative rate of elastic wall extension.

The second Augmented Growth Equation is a mathematical statement describing the net rate of water uptake, and may be obtained from the well-established physical principle, the conservation of water mass (2, 3, 4):

$$ [2] \qquad v_w = (dV_w/dt)/V_w = L(\sigma\Delta\pi - P) - T, $$
where $v_w$ is the relative rate of change in volume of the cell contents (mostly water), $V_w$ is the volume of the cell contents, $L$ is the relative hydraulic conductance of the cell membrane, $\sigma$ is the solute reflection coefficient of the cell membrane, $\Delta\pi$ is the difference in osmotic pressure between the cell sap and the external medium, and $T$ is the relative transpiration rate. The term, $L(\sigma\Delta\pi - P)$, represents the rate of water uptake, and the term, $T$, represents the relative rate at which water is lost from the cell by transpiration. This term, $T$, is zero for cells that are not exposed to the external environment, and thus do not transpire. It should be noted that the volume of the cell contents must equal to the volume of the cell wall chamber, $V_w = V_c$, and that the respective relative rates of change in volume must also be equal, $v_w = v_c$.

Importantly these Augmented Growth Equations, equations 1 and 2, have demonstrated utility in understanding and predicting the growth rate behavior and water transport behavior of higher and lower plant cells, and fungal cells. Furthermore, these equations have proven useful in determining the magnitude and behavior of the inclusive parameters.

Because the turgor pressure, $P$, is a biophysical parameter that is present in three of the four terms of the Augmented Growth Equations, the pressure probe (which directly measures the turgor pressure of single cells) has proven to be an important tool in determining the magnitude and behavior of the biophysical and biomechanical parameters in equations 1 and 2. It is important to note that governing equations for nearly all pressure probe methods can be obtained directly from the Augmented Growth Equations in their present form or by examining them in limiting cases.

In this communication, recent pressure probe methods (and the associated governing equations) that have been developed to determine the magnitude and behavior of relevant biophysical and biomechanical parameters are reviewed, discussed, and evaluated. Some of the pressure probe methods reviewed are: (a) *in vivo* creep and *in vivo* stress relaxation methods to determine the relative irreversible wall extensibility, $\phi$, and the yield threshold, $Y$, of growing cells; (b) pressure pulse-up method to determine the volumetric elastic modulus, $\epsilon$, of non-growing cells; (c) pressure clamp and pressure relaxation methods to determine the cell membrane hydraulic conductivity, $L_p$, and (d) pressure clamp and pressure relaxation methods to determine the relative transpiration rate, $T$, of single cells. Also discussed are some *new* pressure probe methods currently being developed in our laboratory, but not yet published: (e) pressure pulse-up method to determine the volumetric elastic modulus, $\epsilon$, of *growing* single plant and fungal cells; (f) *in vivo* pressure relaxation - transpiration method to determine the *average* volumetric elastic modulus, $\epsilon$, of the cells in plant tissue.

## References

1. Ortega, J.K.E. (1985) Augmented growth equation for cell wall expansion. *Plant Physiol.* **79**: 318-320.

2. Ortega, J.K.E. (1990) Governing equations for plant cell growth. *Physiol. Plant.* **79**: 116-121.

3. Ortega, J.K.E. (1993) Pressure probe methods to measure transpiration in single cells. *In*: Water deficits: Plant responses from cell to community (eds. J.A.C. Smith & H. Griffiths). BIOS Scientific Publishers Limited, Oxford, UK: 73-86.

4. Ortega, J.K.E., Keanini, R.G. and Manica, K.J. (1988) Pressure probe technique to study transpiration in *Phycomyces sporangiophores*. *Plant Physiol.* **87**: 11-14.
ESTIMATION OF GENE ACTION GOVERNING THE MORPHOLOGICAL
ATTRIBUTES IN *Eucalyptus* SPECIES

M.PARAMATHMA and C.SURENDRAN

Forest College and Research Institute
Tamil Nadu Agricultural University
Mettupalayam - 641 301
INDIA

SUMMARY

Six species of *Eucalyptus* viz., E. alba
Reomw-ex., B., E. camaldulensis Dehnh., E. microtheca,
E.Muell, E. tereticornis Sm., E. polycarpa F. Muell
and E. torelliana F. Muell., were subjected to a
complete diallel mating. The experiment was carried
out at the Forest College and Research Institute,
Mettupalayam (11°19'N, 76°56' E, 300m a msl., Rainfall
830 mm; pH 7.1) during 1989-92. The direct as well as
reciprocal crosses involving the two species viz., E.
polycarpa and E. torelliana between themselves or with
other species failed to set seeds. An evaluation of
the other four parents and 12 hybrids for nature of
gene action governing the morphological attributes
indicated that characters like height, collar
diameter, leaf number and leaf breadth were found to
be free from non-allelic interaction. For characters
like internode length, leaf length, suitability index
and volume index, non-allelic interaction was
observed.

For the characters viz., leaf length and leaf
breadth, where predominance of additive genes was
observed, recurrent selection may be the appropriate
strategy for accumulating favourable genes. The
magnitude of dominant genes was high for most of the
other characters investigated indicating the promise
of heterosis breeding for these traits.

Symmetrical distribution of positive and
negative genes was inferred. The gene distribution
among the parents was observed to be unequal with
greater frequencies of dominant alleles for most
characters. Considering economic attributes, the
number of genes that control the characters was one
for collar diameter and leaf length, two for height,
internode length and volume index and three for
suitability index and leaf breadth. In general, the
narrow sense heritability was high for growth
attributes like height and collar diameter.
# Effects of gravity and microgravity on root growth and statocyte polarity

Gérald PERBAL and Dominique DRISS-ECOLE

Laboratoire CEMV, Bât. N2, case courrier 150, Université Pierre et Marie Curie, 4 place Jussieu, F-75252 Paris Cedex 05

Gravitropism, growth of plant organs either towards (roots) or away from gravity (shoots) has been intensively studied in the last decade.

When a root is subjected to a change in orientation in the gravitational field, its extremity bends in order to reorient itself with respect to gravity. The signal of curvature comes from the cap (which is located in the root tip) and is transmitted to the zone of curvature. Bending occurs because of a differential growth in the upper and lower halves of the roots. It is due to an increase of cell growth in the upper part of the distal meristem and a decrease of cell growth in the lower part of the proximal region of the cell elongation zone.

The perception of gravity takes place in special cells (statocytes) which contain voluminous amyloplasts (statoliths). It is generally accepted that these amyloplasts play the role of gravisensors. Their density is greater than that of the surrounding cytoplasm and these organelles therefore sediment in the statocytes. These cells show a strict polarity: their nucleus is attached to the plasma membrane and in contact with it at the proximal cell pole, whereas the endoplasmic reticulum is located along the distal wall beneath the amyloplasts.

In microgravity (in space) this polarity is changed: the nucleus is slightly displaced and separated from the plasma membrane. The endoplasmic reticulum expands toward the cell center. The amyloplasts are not distributed at random but the majority of these organelles is mainly situated near the nucleus at the proximal pole of the cell. It has been proven that actin filaments attach the nucleus to the cell periphery since cytochalasin B (which perturbs the polymerisation of actin) provokes the sedimentation of the nucleus in the statocytes of roots grown on the ground.

The actin network is thus subjected to tensions on the ground and relaxed in microgravity. Both configurations of cytoskeleton could lead to different physiological activities of the statocytes.

On the ground, when a root is subjected for several hours to a gravistimulus, its extremity bends but it never overshoots the direction of gravity. On the contrary, when a root is stimulated for 1h on a centrifuge in space and placed in microgravity, its extremity overshoots the direction of the acceleration which is responsible for the bending of the root. Gravitropic reaction is thus regulated by gravity.

Space research represent a unique opportunity to understand better the action of gravity on plants.
WOOD MOISTURE CONTENT MEASUREMENT
BY X-RAY EXPOSURE METHOD

Patrick PERRE

De-Ku SHANG

ENGREF/14, rue GIRARDET, F-54042 NANCY CEDEX, FRANCE

ABSTRACT

Although quite a number of papers can be found up to now in dealing with the subject of the measurement of wood density by using the X-ray exposure methods, direct scanning or radiographic photography, the following two aspects, which are very important from both theoretical and engineering application points of view, have not yet been properly handled. One is that the elementary analyses or the experimental measurement on the mass attenuation coefficients were not specified in regard to spectrum energy distridutions [1]. In this connection, the ambiguities in the specification of the coefficients and in turn for the results among studies arise when only one of the two parameters, namely wave length and applied voltage, of defining the energy spectrum of X-ray is given. The other is that the relationships between the relative intensity and the sample thickness as well the wood moisture content [2], which are the critical factors for the design and the selection of X-ray apparatus, were not sufficiently examined. In addition, the knowledge of the measurement of wood moisture content by using the direct X-ray scanning method is also almost unavaible now.

In the study, the direct X-ray scanning method of measuring wood moisture content was at first investigated theoretically with respect to the relationship between the mass attenuation coefficients of wood (beech, *Fagus Sylvatica*) and the maximum spectrum energy of X-ray (Table 1). Secondly, the dependence of the relative intensity on the sample thickness and on the wood moisture content was analysed (Fig.1 and Fig.2). The main advantage of the method is on-site nondestructive measuring of wood moisture content in the processes such as drying, impregnation and unsteady mass diffusion. Specifically for the application in the area of biomechanics, the method can also be used for understanding the water pathway within wood, for example, the water around the knots and the relation between the stress distribution and the local moisture content of wood.

Key words: mass attenuation coefficient, maximum spectrum energy, moisture content, relative intensity, sample thickness, X-ray exposure

<figure><img src="image_140.png" /><figcaption>Fig.1 Relative intensity versus wood moisture content for different samples thickness at the maximum spectrum energy of X-ray for the applied voltage 50 kV</figcaption></figure>
<figure><img src="image_141.png" /><figcaption>Fig.2 Relative intensity versus sample thickness of wood for different applied voltage at the maximum spectrum energy</figcaption></figure>

<table><caption>Table 1 The mass attenuation coefficients of wood (beech) and water at the maximum spectrum energy of X-ray and the displacement</caption><thead><tr><th>λ(wave length, Å)</th><th>V(applied voltage, kV)</th><th>Photon energy, keV</th><th>M<sub>a</sub> (wood), cm<sup>2</sup>/g</th><th>M<sub>a</sub> (H<sub>2</sub>O), cm<sup>2</sup>/g</th><th>M<sub>a</sub>(wood)/M<sub>a</sub>(H<sub>2</sub>O), cm<sup>2</sup>/g</th><th>Displacement (λ<sub>max</sub>·V), Å·V</th></tr></thead><tbody><tr><td>9,870</td><td>2</td><td>1,22</td><td>1661,920</td><td>2255,770</td><td>73,67</td><td>19400</td></tr><tr><td>6,390</td><td>3</td><td>1,83</td><td>304,500</td><td>422,740</td><td>72,03</td><td>18060</td></tr><tr><td>3,930</td><td>5</td><td>3,04</td><td>119,710</td><td>167,850</td><td>71,32</td><td>18700</td></tr><tr><td>2,290</td><td>8</td><td>4,87</td><td>23,640</td><td>32,330</td><td>73,14</td><td>18560</td></tr><tr><td>1,930</td><td>10</td><td>6,08</td><td>14,070</td><td>19,330</td><td>72,78</td><td>19200</td></tr><tr><td>1,235</td><td>15</td><td>9,13</td><td>3,870</td><td>5,110</td><td>73,82</td><td>17850</td></tr><tr><td>1,000</td><td>20</td><td>12,17</td><td>2,100</td><td>2,830</td><td>74,21</td><td>18800</td></tr><tr><td>0,710</td><td>25</td><td>15,21</td><td>0,868</td><td>1,132</td><td>76,67</td><td>18500</td></tr><tr><td>0,417</td><td>50</td><td>30,42</td><td>0,317</td><td>0,374</td><td>84,68</td><td>19000</td></tr><tr><td>0,195</td><td>100</td><td>60,83</td><td>0,191</td><td>0,204</td><td>93,63</td><td>19500</td></tr><tr><td>0,161</td><td>120</td><td>73,00</td><td>0,174</td><td>0,187</td><td>93,15</td><td>19320</td></tr><tr><td>0,120</td><td>150</td><td>91,25</td><td>0,162</td><td>0,172</td><td>94,09</td><td>18150</td></tr><tr><td>0,098</td><td>180</td><td>109,50</td><td>0,151</td><td>0,159</td><td>95,01</td><td>18000</td></tr><tr><td>0,072</td><td>250</td><td>152,08</td><td>0,143</td><td>0,150</td><td>95,77</td><td>18000</td></tr><tr><td>0,064</td><td>300</td><td>182,50</td><td>0,137</td><td>0,143</td><td>95,86</td><td>19200</td></tr><tr><td>0,030</td><td>600</td><td>365,00</td><td>0,109</td><td>0,121</td><td>90,10</td><td>18000</td></tr><tr><td>0,024</td><td>1000</td><td>608,33</td><td>0,100</td><td>0,117</td><td>85,50</td><td>24000</td></tr><tr><td>0,010</td><td>1500</td><td>912,50</td><td>0,088</td><td>0,108</td><td>81,50</td><td>15000</td></tr><tr><td>0,005</td><td>3000</td><td>1825,00</td><td>0,070</td><td>0,099</td><td>70,70</td><td>15000</td></tr></tbody></table>

REFERENCES

[1]. Weast, R.C. and Selby, S.M. (editors), 1968. Handbook of Chemistry And Physics, 48th Edition, The Chemical Rubber Co. Publisher, Ohio.

[2]. Olson, J.R., 1981. Prediction of Mass Attenuation Coefficients of Wood, Wood Sciences, 14(2):86-90.
BIOMECHANICS OF GRASSES

- Functional-morphological studies using finite element method -

U. Philippi, A.B. Kesel, W. Nachtigall

Universität des Saarlandes, Fb 13.4 Zoologie, D-66041 Saarbrücken

Grasses are slim high constructions. Depending upon their surrounding environment, they must possess certain characteristics in order to withstand the pressures of selection. The self-supporting construction "grass" must take into account a variety of different pressures and combination of pressures according to the physical boundary conditions (environment) (e.g. Schwendener 1874). Disregarding the dynamic aspects for the time being, the bending stability leads to four biomechanic loading models:

**MODEL I:** No wind, loading along the blade axis results exclusively from the weight of the head (Fig. 1).

In nature, this type of loading is rarely found in a blade of grass. The head is usually eccentric.

**MODEL II:** No wind, loading due to the weight of head is eccentric (Fig. 2).

However, the two problems mentioned can be solved analytically only if the blade of grasses is taken to be constant or at least constant in sections. Furthermore, only concentrated single forces and not widespread attacking forces are assumed. This single force, the weight force of the head, may not exceed at certain critical value $F_c$ otherwise the blade will snap over.

Normally, the blade will not only be influenced by the weight of its head, but also by the wind load $F_w$.

<figure><img src="image_142.png" /><figcaption>Fig 1: MODEL I</figcaption></figure>

<figure><img src="image_143.png" /><figcaption>Fig 2: MODEL II</figcaption></figure>

**MODEL III:** Blade under wind and head loading (Fig. 3).

Wheras the snaping force caused by the head froms the main loading component with a low wind force, the bending strain on the blade increases with increasing wind force. This bending strain is dependent directly upon the wind, since blade deformation is depend upon the attacking load.
### MODEL IV: Blade under strong to maximal wind load (Fig. 4).

The greater the wind load, the more the blade will evade it. At maximum wind loading, the blade stalk is attacked mainly by tangential forces. Strong bending forces occur only at the base.

<figure><img src="image_144.png" /><figcaption>Fig 3: MODEL III</figcaption></figure>

<figure><img src="image_145.png" /><figcaption>Fig 4: MODEL IV</figcaption></figure>

Both these cases are non-lineare problems. If one wishes to avoid non-linear calculations, one must use iterative methods. Once adequate models have been built, the holding behavior of grasses under the types of loading described can be analysed using the Finite Element-Method (Niklas 1977). This method enables one to take into consideration the distribution and arrangement of tissues gained from histological and morphological studies.

Because of the biomechanical importance of the nodes (Niklas 1989, Gappoev 1991) the various distribution were taken into consideration when calculating MODEL III and leads in two construction typs: A) even distribution along the stem B) concetrates at the base of blade. The blades (L: 0.55 m) were fixed at the base and loaded with line load which is equivalent to a wind speed of 8 m s⁻¹.

The two construction types show little deviation with regard to their deflection in the x- or y-direction (3 % resp. 6 %). Due to the greater stiffness created by the distribution of nodes along the entire blade, the bending moments are increased approximately 3.5 times in this type of construction, and the axial forces and tensions are reduced by 50 % compared to type B. The latter does not appear to have any advantages despite its more complicated construction. First calculation on MODEL IV however suggest a greater degree of security.

From these analysis, one gains valuable indications of eventual restrictions or peculiarities regarding habitat, propagation etc of grasses which result from their construction.

### References:

* Gappoev M. 1991. Untersuchung zur Form und Faserstruktur von Gras- und Halmpflanzen unter Berücksichtung der Kräfteverteilung in den Knoten. Mitteilungen des SFB 230, Heft 6, Stuttgart.

* Niklas K.J. 1977. Applications of Finite Element Analyses to problems in plant morphology. Ann. Bot. 41: 133.

* Niklas K.J. 1989. Nodal septa and the rigidity of aerial shoots of *Equisetum hyemale*. Amer. J. Bot. 76 (4): 521.

* Schwendener S. 1874. Das mechanische Prinzip im anatomischen Bau der Monocotylen mit vergleichenden Ausblicken auf die übrigen Pflanzenklassen. Engelmann, Leipzig.
# THE BIOPHYSICS OF ROOT GROWTH

Jeremy Pritchard and Deri Tomos

School of Biological Sciences, UCNW, Bangor, Gwynedd LL57 2UW,
Wales, UK. Tel- (0248) 370731

**Growth, turgor pressure and temperature:** Roots increase in length as a result of the expansion of single cells in the root apex. Changes in turgor pressure and/or the properties of the cell wall might be expected to affect cell expansion. This is described by the equation;

$$r = \phi (P - Y) \qquad \text{equation 1}$$

where r = growth rate, P = turgor pressure. φ and Y are the wall extensibility and the yield threshold respectively and are physical properties of the cell wall. The relationship described in equation 1 can be demonstrated experimentally (Fig 1).

<figure><img src="image_146.png" /><figcaption>**Figure 1:** Turgor pressure of the growing zone vs growth rate of hydroponically grown maize roots. The reduced slope of the relationship at 15°C indicates a reduction in φ.</figcaption></figure>

As turgor pressure of the growing zone, measured with the pressure probe (1), is lowered by incubation in different mannitol solutions, root extension rate is also reduced. In maize roots growth ceased at around 0.2 MPa at 30°C. This pressure is the yield threshold of equation 1. The slope of the line is the wall extensibility (φ). In common with other organs, roots grow slower at lower temperatures. This reduction in growth is not due to a change in yield threshold or turgor pressure but is caused by a reduction in wall extensibility (Fig.1).

**Development, osmotic stress and cell wall properties:** The growing zone consists of columns of many expanding cells, which can respond in different ways during development and in response to changes in the environment. The growth rate along the root apex has a characteristic bell shaped distribution (Fig.2a).
This variation in growth must also be due to changes in cell wall properties since the turgor pressure (the driving force for expansion) along the same region is constant (Fig.2b).

<figure><img src="image_147.png" /></figure>

**Figure 2:** Profiles of growth rate (2a) and turgor pressure (2b) along the apical 12 mm of maize roots under different osmotic stresses. Changes in growth rate despite a relatively constant turgor indicates changes in cell wall properties.

The relationship between turgor pressure, growth rate and wall properties is a dynamic one. If turgor pressure is reduced along the growing region, 15 minutes later growth rate is reduced in the region 7-10 mm but remains unchanged 0-3 mm from the root tip (Fig.2a). Since turgor pressure is reduced but growth rate remains unchanged the cell walls must have become looser. If roots experience a prolonged (24h) osmotic stress turgor pressure recovers along the whole growing zone. In contrast growth rate remains low in the proximal region but is the same as unstressed roots nearer the tip. Cell wall properties are therefore tighter in the proximal region but are unchanged in the root apex.

**Soil and root growth:** Roots grown in soil of high density have a reduced growth rate in comparison to those in loose soil. This reduction in growth is accompanied by a reduction in mature cell length. Evidence (obtained using tensiometric methods) suggests that this is due to a tightening of the cell wall (a decrease in φ or an increase in Y).

**Summary:** Thus root growth is the result of the interaction of turgor pressure and wall properties leading to alteration in growth rate by a variety of different environmental stresses. The changes in cell wall properties have their basis in changes in the cell wall biochemistry. It is becoming apparent that enzymes which catalyse the formation and breakage of cross linkages between wall components may be responsible for some of the effects mentioned above. These include wall peroxidases (2) and xyloglucan endotransglycosylase (3). Further characterisation of the effect of the environment on root cell biophysics and the correlation of this with changes in biochemistry will lead to a deeper understanding of growth processes in roots.

## References

1) Hüsken D et al (1978) *Plant Physiol.* 61 158-63.

2) Pritchard J & Tomos A D (1993). In "Water deficits" eds. JAC Smith & H Griffiths, Bios, Oxford pp.53-71.

3) Pritchard et al (1993) *J.Exp.Bot.* 44 1281-1289.
# Underground Plant Movement by Contractile Roots. An Experimental Approach to the Functionality of Channel Formation

N. Pütz, G. Hüning, Botanisches Institut der R.W.T.H. Aachen, D-52056 Aachen

Contractile roots develop a pulling force to overcome soil resistance (Pütz 1992). This pulling force produces underground movement of the plant body, e.g. a bulb, corm or rhizome. The distance moved by the plant is in most cases only a few centimetres (e.g. Nothoscordum inodorum, Alliaceae, Pütz 1993). However, some species show a movement of 20 cm and above in the course of a single vegetation period (Oxalis pes-caprae, Pütz 1994).

Plants are helped to move by the channel effect. The contractile root increases in diameter and forms a channel in the soil through which the plant body can move without soil resistance. The channel effect in contractile roots varies from species to species. A few species show no channel effect (e.g. Sauromatum guttatum, Pütz 1992), while others show a 100% channel (Oxalis pes-caprae, Pütz 1994, Triteleia hyacinthina, Pütz 1992). In most cases, the channel effect varies between 10 to 40% (Pütz 1992a).

Thus, energetically considered, there are two forces working together when a plant body moves in the soil:

1. a **pulling force** for overcoming soil resistance

2. a **pushing force** for displacing soil to form a channel.

Using a new modeling technique we were able to simulate the underground movement of a bulb. We measured the pulling force necessary to move different distances in relation to various channel effects. A second new method proved useful in calculating the pushing force necessary to form different soil channels.

Conclusions about the energetics involved can be drawn from comparing these different forces. It can generally be demonstrated that a channel effect favourably influences underground plant movement. However, differences in effect can be shown. A channel of 10 or 40% is optimal if the distance to be moved is relatively low (20-30 mm). However, the formation of a 100% channel effect seems to be advantageous if the distance traveled reaches 50 mm or higher.

These energetic conclusions correspond very closely to field observations. The channel effect in bulbous plants showing underground movement of 10-30 mm is normally small (Pütz
1992a). However, in every species where greater movement is found, a 100 % channel effect seems always present (Pütz 1992, 1994)

## Literature:

PÜTZ, N., 1992: Measurement of the pulling force of a single contractile root. - Can. J. Bot. 70, 1433-1439.

-- 1992a: Das Verhältnis von Bewegung und Wurzelkraft bei Monokotylen. - Beitr. Biol. Pfl. 67, 173-191.

-- 1993: Underground plant movement. I. The bulb of Nothoscordum inodorum. - Bot. Acta 106, 338-343.

-- 1994: Underground Plant Movement. II. Vegetative Spreading of Oxalis pes-caprae.- Plant. Sys. Evol. (in press).
# Water transport in vessel elements with helical thickenings

A. Roth

Institut und Museum für Geologie und Paläontologie

Sigwartstr. 10, D-72076 Tübingen, Germany

The water-conducting tissue of a vascular plant, the xylem, provides a low-resistance pathway for water transport. The high water permeability of the xylem is achieved by programmed cell death of its elements. Longitudinal water flow occurs in the resulting void spaces. Vessel elements show thickened and lignified cell walls which are required in order to withstand the mechanical forces due to the negative pressure gradient occurring during transpiration.

The structure of the inner sides of vessel elements is dependent on the development of the secondary wall. The first vessel elements to be differentiated show annular or helical arrangement of the secondary wall due to local deposition of wall material. These are followed by reticulate elements. Finally, vessel elements with pitted walls develop in the metaxylem. At this stage in the ontogenetic sequence, the secondary wall covers almost the entire area of the primary wall. Helical sculptures on the inner surface are, however, not only a feature of the protoxylem as spiral thickenings may also be present in elements of the secondary xylem. The frequency of their occurrence in secondary wood tends to be a function of climatic factors, as was reported by Baas & Schweingruber (1987). A satisfactory functional interpretation of helical thickenings in secondary wood is, however, still lacking (Baas 1986). As was shown experimentally by Jeje & Zimmermann (1979), certain geometric parameters of helical thickenings and their arrangement influence the friction drag acting on water as it passes through a vessel. Thus, the structure of helically sculptured inner surfaces of vessels contribute to the water transport properties of xylem. They speculated that the observed effects can be explained by a limited "slip flow" occurring between the rings.

In the present study, the water flow through vessels with various patterns of helical thickenings was investigated using a fluid mechanical approach suitable for simulating the flow in a single capillary with a sculptured inner surface. For this purpose, a commercial CFD (Computational Fluid Dynamics) - programme (FIDAP) based on the Navier-Stokes-equations which are solved using the Finite Element Method (FEM) was used. The programme readily allows for the construction of arbitrarily complex wall structures. This approach was successfully used by Schulte & Castle (1993), who investigated the hydrodynamic effect of scalariform perforation plates.

Examples of the results are shown in Figs. 1 and 2. Figure 1 represents the FE-grid of an axisymmetrical structure (longitudinal axis of rotation at the left) with a radius of 25 µm and with helical thickenings (width of rings: 23 µm, height of rings: 10 µm and distance between rings: 10 µm). The lumen of the vessel is divided by the FE-grid, whereas the helical thickenings are represented by the white rectangles. The pressure gradient occurring along the helical zone amounts to about 90% of the gradient which is present when the gaps between rings are completely filled with wall material. The pressure gradient can be increasingly reduced by changing such parameters as the distance between the rings as well as their width. As is shown by Fig. 2 (a magnification of a region between two adjacent
wall protrusions), the decreased pressure gradient is due to the presence of a "recirculation zone" between the rings. In this manner, a "limited" slip flow at the interhelical zones is generated.

<figure><img src="image_148.png" /><figcaption>Figure 1: The FE-grid.</figcaption></figure>

<caption>Figure 2: Fluid movement between two adjacent rings.</caption>

The results demonstrate the effects of internal sculpturing of vessels on water flow. It may be speculated that helical thickenings in vessels represent an interaction of mechanical and hydrodynamical requirements, thus reflecting an optimization process.

References:

Baas, P. 1986 Ecological patterns in xylem anatomy. In: On the economy of plant form and function. (ed.: T.J. Gvinish):327-352

Baas, P. & Schweingruber, F.H. 1987 Ecological trends in the wood anatomy of trees, shrubs and climbers from Europe. IAWA Bull. n.s. 8:245-274

Jeje, A.A. & Zimmermann, M.H. 1979 Resistance to water flow in xylem vessels. J. exp. Bot. 30(117):817-827

Schulte, P.J. & Castle, A.L. 1993 Water flow through vessel perforation plates - a fluid mechanical approach. J. Exp. Bot. 44(264):1135-1142
# Morphogénèse et fermeté de la pomme

A.-C. Roudot*, C.J. Studman**, F. Duprat***

* Ecole Supérieure de Microbiologie et Sécurité Alimentaire
Technopôle Brest-Iroise
29280 Plouzané

** Massey University
Department of Agricultural Engineering
Palmerston North
Nouvelle Zélande

***Institut National de la Recherche Agronomique
Laboratoire de Méthodes Physiques d'Etude
Domaine St Paul
BP 91
84143 Montfavet cedex

Lors des études expérimentales de la fermeté des pommes, on trouve une grande variabilité de ce paramètre, que les mesures soient faites sur la périphérie du fruit ou réparties sur une tranche (1). L'origine de cette hétérogénéité est encore peu claire, on invoque divers paramètres agronomiques, climatiques, ou autres, mais aucune certitude n'est acquise dans ce domaine à l'heure actuelle.

La simulation numérique est un moyen efficace de tester les divers paramètres supposés intervenir dans cette hétérogénéité. La méthode utilisée dans ce travail consiste à appliquer des procédés de simulation de croissance sur des modèles préalablement définis par modélisation histologique. Cette modélisation est une méthode de caractérisation physique des milieux cellulaires qui tient compte de l'hétérogénéité de distribution et de dimension des cellules au sein d'un tissu. Son intérêt majeur réside dans sa facilité à représenter des structures cellulaires complexes sans nécessité de simplification outrancière au niveau de la géométrie (2).

Dans cette simulation, le processus de croissance est essentiellement géométrique, seules quelques rares conditions mécaniques ont été utilisées. Le modèle présenté est bidimensionnel, les quelques différences apparaissant dans sa comparaison avec des essais tridimensionnels, ne justifiant pas les contraintes de temps de calcul et de taille mémoire nécessitées par un traitement 3D.

On suppose que dans un premier temps, la division cellulaire sera le phénomène prépondérant et que la croissance ne prendra toute son ampleur que dans un second temps après que les divisions soient achevées. Les cellules en croissance sont considérées comme des sphères en contact les unes avec les autres. La contrainte mécanique de chaque cellule (que nous assimilerons à sa fermeté) augmentera dans deux cas:

- lorsqu'elle entrera en contact avec une autre cellule voisine. Dans ce cas leurs contraintes mutuelles augmentera selon la loi de Hertz. Ceci peut se produire lorsqu'une cellule
voit son volume croître et nécessite un espace vital plus important qu'auparavant, et lorsque
suite à une croissance, des cellules voisines sont obligées de se réarranger localement, et donc
de se déplacer les unes par rapport aux autres, pour laisser un espace libre suffisant afin que la
croissance s'effectue convenablement.

- du fait de la présence de la peau du fruit. Celle-ci exerce un effort qui s'oppose à la croissance globale de la pomme, et a donc pour effet de créer une pression externe qui est supposée d'autant plus forte que le fruit est gros.

La croissance est anisotrope du fait de la différence de rigidité mécanique entre l'axe principal du fruit et un rayon perpendiculaire. Cet effet est modélisé en renforçant la contrainte externe due à la peau lorsque l'on se rapproche de l'axe principal.

Les résultats des diverses simulations effectuées montrent que globalement le fruit a une forme proche de la réalité, mais surtout que les contraintes (ou les fermetés) peuvent varier dans une gamme allant du simple au triple. Globalement la fermeté maximale se situe dans la zone interne, elle diminue ensuite en s'éloignant du coeur du fruit pour augmenter légèrement au niveau de la peau. Enfin, ces simulations montrent une hétérogénéité de distribution des fermetés, certaines zones pouvant être plus fermes que d'autres bien que situées plus à l'extérieur du fruit. La totalité de ces observations effectuées en simulation correspond aux résultats obtenus lors de manipulations réelles.

Il semble donc qu'une part importante, voire largement prépondérante, de l'hétérogénéité de distribution de la fermeté dans la pomme soit liée au processus de croissance, et puisse être rattachée à des considérations géométriques de remplissage d'un volume par des sphères en croissance.

1- F. Duprat, F. Roudot, M. Grotte-Nicolas, A.-C. Roudot, 1991
De l'hétérogénéité des fruits
*Sciences des Aliments*, **11**, 613-626

2- C. Wenian, F. Duprat, A.-C. Roudot, 1991
Evaluation de l'importance de la géométrie du tissu cellulaire dans les déformations observées
sur les pommes après une compression ou un choc
*Sciences des Aliments*, **11**, 105-116
# Fossil plants: biomechanics as an aid to interpreting growth form and habit

Nick P. Rowe<fnref n="1" /> and Thomas Speck<fnref n="2" />

Reconstructions of the size and growth form of fossil plants have important implications on the evolutionary processes and ecological mechanisms occurring in plant ecosystems. However, a major problem in determining the overall size, habit and ecology of extinct plants originates from the consistently disarticulated nature of the fossils.

Experimental findings of extant plants demonstrate that self-supporting and non-self-supporting plants (eg. lianas and semi-self-supporting plants) differ significantly in their bending mechanical properties such as Young's modulus and flexural stiffness and in the variation of these properties during ontogeny (Speck 1991). All tested extant self-supporting woody plants show an increase in Young's modulus during ontogeny. In all tested lianas the Young's modulus decreases during ontogeny to 15%-25% of the values found in the youngest ontogenetic stage. Changes in stem mechanics during ontogeny are correlated with shifts in anatomy and contributions of stem tissues towards the cross sectional area and axial second moment of area (Speck 1991, 1994).

In the two extant semi-self-supporting plants experimentally studied up to now, a more or less constant Young's modulus during all ontogenetic stages is found. These plants show neither a marked increase (self-supporting) nor decrease (non self-supporting) in the Young's modulus from young to older ontogenetic stages.

These differences observed in Young's modulus and flexural stiffness of living plants have been employed to distinguish self-supporting and non self-supporting habits among long extinct fossil plants. Different ontogenetic stages of anatomically preserved stems are arranged according to their ontogenetic sequence. For each level, the geometric distribution of tissues: pith, wood, sclerenchyma etc. is measured and installed into a model describing the distribution of tissue types for each stage. Analytically derived formulae describing the tissue distribution are used to determine the contribution of each tissue type to cross-sectional area and axial second moment of area of the stem. Each tissue type is correlated as closely as possible in terms of wall thickness, cell shape, ornamentation and pitting with extant plant tissues for which the Young's modulus has been experimentally determined. By considering the fossil plant stems as composite materials, the flexural stiffness and Young's modulus of the entire plant stem and the contribution of each stem tissue to flexural stiffness can be calculated. As in modern plants the variation of these parameters is assessed over differing ontogenetic stages and the habit of the fossil plant is inferred. Our studies focus on growth forms among early seed plants that showed

<footnote n="1">¹Université de Montpellier II, Institut des Sciences de l'Evolution, Laboratoire de Paléobotanique et Evolution des Végétaux, F-34095 Montpellier, France.</footnote>

<footnote n="2">²Botanischer Garten der Albert-Ludwigs-Universität, Schänzlestr. 1, D-79104 Freiburg, Germany.</footnote>
a rapid radiation and morphological differentiation during the Lower Carboniferous. Biomechanical analyses of *Calamopitys* and *Lyginopteris oldhamia* stems suggest that both were semi-self supporting (Speck & Vogellehner 1992, Rowe et al. 1993, Speck 1994). Semi-self-supporting plants may have either a scrambling growth mode or a habit as social plants living in dense stands, characterized by individuals providing mutual support from densely interacting fronds or branches. The mechanical parameters of semi-self-supporting early seed plants rely mostly on hypodermal support and not on secondary wood.

The mechanical parameters of these semi-self-supporting taxa are compared with results for *Pitus dayi* in which a hypoderm is not developed and in which a periderm is rapidly established. A rapid shift in mechanical support occurs from one dominated by support from the leaf traces, wood and parenchymatous cortex to one dominated by wood and periderm. The appearance of a truly self-supporting habit among seed plants and its significance in the evolution of plant communities is discussed with reference to recent biomechanical studies of Palaeozoic self-supporting and non-self-supporting seed plants and to late Devonian progymnosperms.

Rowe, N. P., Speck, T. & Galtier, J. (1993) Biomechanical analysis of a Palaeozoic gymnosperm stem. Proc. R. Soc. Lond. B, **352**: 19-28.

Speck, T. (1991) Changes of the bending mechanics of lianas and self-supporting taxa during ontogeny. Proc. II. Int. Symp. Sonderforschungsber. 230, part I. Mitt. SFB 230, **6**: 89-95.

Speck, T. (1994) A biomechanical method to distinguish between self-supporting and non self-supporting plants. Rev. Palaeobot. Palynol. (in press).

Speck, T. & Vogellehner, D. (1992) Fossile Bäume, Spreizklimmer und Lianen. Versuch einer biomechanischen Analyse der Stammstruktur. Cour. Forsch.-Inst. Senckenberg, **147**: 31-53.
# An ultrastructural study of the qualitative distribution of lignin in a developing internode of maïze

Katia RUEL and Jean-Paul JOSELEAU

Centre de Recherches sur les Macromolécules Végétales (CERMAV-CNRS)

B.P. 53 X 38041 Grenoble-cedex, France.

The description of the ultrastructural organization of polysaccharides and lignin in the plant cell wall is of great importance for the understanding of the role of these macromolecules in the cell wall cohesion. In particular, lignin distribution is of great importance in this domain.

In Gramineae, lignin has a great complexity because it is made of three different monomers which give rise to three types of lignin : p-Hydroxyphenyl (H), Guaiacyl (G) and Syringyl (S). The relative distribution of the three types of lignin has been determined in a developing internode of maïze by means of immunocytochemical markers. To that effect antibodies were prepared against the three types of lignin.

The results showed differences in the overall lignification of the different tissues and variations in the intensity of the labelling by the different markers as a function of maturation.

The most characteristic result was that all the different types of lignin seem to be evenly distributed throughout the secondary wall, without preferential localization of a given type.

Another interesting observation was the different reactivity of the middle lamella versus the secondary walls. This variation in reactivity may correspond to differences in the respective content of condensed lignin in these parts of the plant cell walls.
# STANDING TREE QUALITY ASSESSMENTS USING ULTRASOUND

J.L. Sandoz<fnref n="1" />), P. Lorin<fnref n="2" />)

Trees are organic vegetal materials forming an important link in the carbon turn-over cycle. In the forest, they are associated together in the eco-system. In the cities, they act singly in ecological and decorative functions.

Quality assessments of standing trees may be considered to have two separate targets: biological internal quality related to the wood degradability and elastic quality of the heartwood regarding the industrial valuation of the wood products.

Biological internal quality of standing trees can be non-destructively evaluated using ultrasound. The speed of a low frequency wave propagated on the radial axis of the tree is measured. Compared to a referential speed for each species, deviation of the speed is considered to be indicative of degraded wood. Diameter and seasoning effects must be taken into account for better accuracy of the diagnostics.

Elastic quality of the wood contained in the tree can be evaluated by ultrasound. In this application, speed of sound is measured on the longitudinal axis in the sapwood area. Dispersion of the results in terms of speed is the basic information allowing a first step in grading the internal wood material.

<footnote n="1">1) Professor J.L. Sandoz
EPFL-IBOIS, GCH2-Ecublens, CH-1015 Lausanne
Tel. (+41-21) 693 39 30, Fax (+41-21) 693 23 94</footnote>

<footnote n="2">2) Ing. P. Lorin, scient. assistant
EPFL-IBOIS, GCH2-Ecublens, CH-1015 Lausanne
Tel. (+41-21) 693 39 30, Fax (+41-21) 693 23 94</footnote>
Contraintes de Croissance et Morphologie
chez un clone de Peuplier (I214)

François SASSUS, Rémi THOMAS, Valérie GRZESKOWIAK,
Bernard CHANSON, Mériem FOURNIER, Bernard THIBAUT

Université Montpellier II - LMGC-Bois - CP081 - Place E. Bataillon, 34095 Montpellier Cedex 5 (FRANCE)
tél. (33) 6714 3431, 3483, 3433, 4739 - fax (33) 6754 4852

L'élaboration du champ de contraintes est influencé par des facteurs morphogénétiques :

1. l'inclinaison de l'arbre (Polge, Ferrand, Saurat&Guéneau, Nicholson),

2. le phénomène de réorientation (Fournier, a),

3. le phototropisme (Kubler),

4. le plan d'organisation de l'arbre (Chanson).

Le but de l'étude est d'approfondir les relations entre la morphologie de l'arbre et le champ de contraintes de croissance à l'intérieur.

Cinq peupliers, en âge d'exploitation, ont été choisi pour leurs particularités : un arbre de lisière, un arbre droit et incliné avec une fourche équilibré, un arbre courbe et incliné avec une fourche basse et importante, un arbre droit vertical et élancé, un arbre avec une courbure importante. Les arbres sont écorcés sur 6 m. Des mesures de déformations de maturation (Fournier, b) sont réalisées avec un capteur extensométrique après libération des contraintes (méthode du "trou unique"). Elles sont effectuées sur une couronnes de 8 points (fig 1) à des hauteurs à priori stratégiques (aux départs d'axes réorientés, aux points de courbure importante, etc.).

Nous avons ensuite abattu les arbres pour prélever des billons aux endroits des mesures. Le bois de tension est détecté sur les rondelles entières en utilisant un colorant macroscopique (chloro iodure de zinc), après avoir vérifier sa spécificité sur une "rondelle test".

On peut voir les résultats suivants sur les profils de déformations de maturation :

* l'arbre de lisière est "tiré" vers la lumière, les pics de tension se situent de manière inhabituelle sur la face inférieure de l'arbre (fig 2). Le phototropisme du Peuplier est marqué et influence la mise en place des contraintes de croissance ;

* l'importance de l'inclinaison, l'arbre vertical a un profil plat avec des valeurs faibles, alors que les arbres penchés ont un maximum fort sur la face supérieure (sauf arbre de lisière);

* la courbure est le siège de valeurs fortes (fig 3), les contraintes de croissance permettent à l'arbre de garder (au maximum) une direction de croissance verticale.

Grâce aux données récoltées, nous chercherons d'abord à estimer la mesure à partir de la coloration (en affectant un poids aux zones de fibres G). Ensuite à étudier la variation de la mesure sur de faibles écarts de hauteur. Et enfin, à réaliser les cartographies de bois de tension, qui nous permettront de relier l'apparition du bois de réaction au différents phénomènes morphogénétiques.
Bibliographie

CHANSON B., 1992 - Hétérogénéités angulaires des déformations de maturation : interprétation basée sur le concept de plan d'organisation des arbres - Acta bot. Gallica, 1993, 140(4), 395-401.

FERRAND J.C., 1981 - Recherches des solutions pratiques à apporter aux problèmes posés par les contraintes de croissance des arbres forestiers - Thèse INPL.

FOURNIER M.(a), 1989 - Déformations de Maturation, Contraintes "de Croissance" dans l'arbre sur pied, réorientation et stabilité des tiges - publication ASMA - LMGC bois, USTL, Montpellier.

FOURNIER M., 1991 - Mécanique de l'arbre sur pied : modélisation d'une structure en croissance soumise à des chargements permanents et évolutifs. 2.analyse tridimensionnelle des contraintes de maturation, cas du feuillu standard.

NICHOLSON J.E., HILLIS W.E., DITCHBURNE N. - 1975 - Some tree growth wood property relashionships of eucalyptus. Canadian journal of Forest Research 5(3) 424-432;

POLGE H., 1981 - Influence of the thinning regime on growth stresses in beech. Annales des Sciences Forestières 38 (4) 407-423.

SAURAT J. & GUÉNEAU P., 1976 - Contraintes de croissance dans le Hêtre. Wood Science and Technology 10(2) 111-123.

<figure><img src="image_149.png" /></figure>

<figure><img src="image_150.png" /></figure>
# Studies on the wood degrading basidiomycete *Inonotus hispidus*; an assessment of the different impact on the physical properties of partially decayed ash and London plane wood

F.W.M.R. Schwarze¹, D. Lonsdale², C. Mattheck³ and S. Fink¹

¹Albert-Ludwigs-Universität Freiburg, Insitut für Forstbotanik und Baumphysiologie, Bertoldstr. 17, 79098 Freiburg i.Br., Germany. ²Forest Authority Research Station, Alice Holt Lodge, Farnham, Wrecclesham, Surrey, GU10 4LH GB. ³Institut für Materialforschung, Kernforschungszentrum Karlsruhe GmbH, Postfach 3640, 76021 Karlsruhe, Germany.

## Abstract

The wood degradation pattern of *Inonotus hispidus* was studied on naturally and artificially infected ash (*Fraxinus excelsior*) and London plane (*Platanus x hispanica*) wood. For *in vitro* studies wood samples from the two hosts were used, these being 18 cm³ blocks.

After both six and twelve weeks incubation, the highest weight losses and moisture contents were recorded on London plane wood. Cell wall degradation of *I. hispidus* in ash and London plane wood is predominantly reminiscent of that described by Courtois (1963) for soft-rot fungi (ascomycetes and fungi imperfecti) of the form-group 11. Cell wall degradation resulted in chains of minute biconical cavaties, joined by proboscis hyphae, following the orientation of the cellulose microfibrillar axis. Penetration hyphae of *I. hispidus* tend to branch repeatedly in the wood cell wall and hyphal alignment with the cellulose microfibrillar axis in the S₁ and S₂ layer of fibre and fibre tracheid cell walls is often consistent. Once single cavaties merge the degradation pattern caused by *I. hispidus* results in the appearance of sphaerical tunnels arranged in a steep helix within the S₂ layer and in a shallow helix within the S₁ layer. Due to the different alignment of the cellulose microfibrillar axis within the two layers tunnels frequently overlap each other when observed in longitudinal sections.

At an early stage of decay in ash *I. hispidus* was found to exhibit a preferential attack of the xylem rays and early wood vessels, whereas in London plane the xylem rays and vessels remained intact even at a very advanced stage of decay. The two different wood degradation patterns caused and described by *I. hispidus* on ash and London plane and the resulting impact on the strength and stability of partially decayed wood provides a reasonable explanation for the tendency that infected branches and stems of ash are far more likely to fail than those of London plane.
# Mechanical aspects of new SEM observations on the fibril/matrix structure of the S2 layer of softwood tracheids

Jürgen Sell, Swiss Federal Laboratories for Materials Testing and Research (EMPA), Wood Department, CH-8600 Dübendorf

## 1. Introduction

The relevant literature on the ultrastructure of wood describes its cell wall as an arrangement of lamellae with different thicknesses and different portions of their main chemical compounds (cellulose, hemicellulose, and lignin). The helical orientation of the cellulosic fibrils or their inclination to the longitudinal cell axis, respectively, is also different for the distinct layers of the secondary wall: the thin S1 (adjacent to the compound middle lamellae, MCL), the thick S2, and the thin S3 (adjacent to the cell lumen) [e.g. Core et al. 1979; Coté 1967; Fengel, Wegener 1989; Liese 1970].

With respect to its obvious importance for the mechanical functions of wood, the ultrastructure of the thick S2 is especially interesting. This structure has been described not always consistently. However, several authors postulate a S2 model consisting of thin concentric and helical lamellae with little, but slightly different inclinations (5° to 30°) to the cell axis [Braun 1992; Liese 1970; Ruel et al. 1978], fig. 1.

In the course of high-resolution SEM studies on transverse-fracture surfaces of tension-loaded samples of softwood (Picea abies, Abies alba, Pinus sylvestris, and others) significant indications have been found that the S2 structure exhibits a sandwich-like assembly of the fibrils with the following characteristics [Sell, Zimmermann 1993], fig. 2.

* The fibrils of the S2 are agglomerated radially to the cell axis: The tangential thickness of these agglomerations is 100 to 1000 nm. Radially, they often extend from the S1 to the S3.

* The bonds between the distinguishable S2 fibrils (diameters between 20 and 100 nm) are stronger in the radial than in the tangential direction (related to the cell axis). Also the adhesion to the adjacent layers S1 and S3 seems to be stronger then the tangential bond within the S2.

A modified model of the entire cell wall of softwood has been proposed [Sell, Zimmermann 1993], fig. 3. The radial arrangement of the structure elements of the S2 has meanwhile been confirmed by the light microscope [Sell 1994], fig. 4.

## 2. Mechanical aspects of the sandwich-like structure of the cell wall

The proposed radial fibril assembly within the S2 or, in other words, fibril agglomerations perpendicular to the "cross-banding faces" S1 and S3 would obviously be beneficial to the mechanical properties of the entire tree. The bending stiffness and thus the buckling resistance of such a sandwich-like cell wall under longitudinal compressive load might be markedly higher then with a cell wall consisting of concentric lamellae. Therefore, the bending stiffness of the whole stem would be improved when loaded by wind pressure or by forces of gravity. This is particularly important for wood with moisture contents (MC) close to or above the fiber saturation point where the strength of wood is significantly reduced. This is the case for the compression zone of a living tree under bending load which lies in the outer sapwood where the MC by far exceeds the saturation point. By the following model test (carried out by K. Timmermann), we tried to illustrate the functional advantage of such a cell wall structure.

## 3. Bending stiffness of two wall models

*Material and methods:* Bending test of 270 mm long rods, cross section 12x14 mm², consisting of glued beech veneers (1 mm thick). Two types (6 replicas each) of the arrangement of the veneers of the 12 mm thick core layer: "standing" veneers (directed parallel to the bending load) and "lying" veneers (perpendicular to the bending load), see fig. 5. The first type is supposed to represent the new S2 model and the latter the former model. The face layers representing the S1 and S3 are identical for both types with a slope of grain perpendicular to that of the middle layer. The veneers were glued using a PVAC-dispersion glue of rather little moisture resistance similar to the "glue" between the S2 fibrils. Conditions of the standardised bending test: (1) application of the load at a temperature of 23°C and an equilibrium wood
MC of 12%, (2) loading at a temperature of 50°C and 12% MC, (3) loading after 24 hours water-submersion of the samples at a temperature of 23°C and a wood MC between about 50 and 65%.

The results are summarised in fig. 5. As to be expected, there is no significant difference of the stiffness of the two sample types tested at normal temperature under dry conditions when the bond of the PVAC glue is not reduced. However, when an increased temperature and particularly a high wood MC reduces the glue bond markedly, the bending stiffness of the sample with "standing" veneers in the middle layer is only reduced by approx. 25 or 50%, respectively. Contrary to that, the bending stiffness of the samples with "lying" veneers is reduced by approx. 75 to 100%, respectively. The results may illustrate the beneficial role of "standing" structure elements of the S2 layer to the stiffness of the wood cell wall.

<figure><img src="image_151.png" /></figure>

## Literature

* Braun, H.J. 1992. Bau und Leben der Bäume (3. Aufl.) Verlag Rombach Freiburg

* Core, H.A., Coté, W.A., Day, A.C. 1979. Wood structure and identification. Syracuse Univ. Press, New York

* Coté, W.A. 1967. Wood ultrastructure - An atlas of electron micrographs. Univ. of Washington Press, Seattle

* Fengel, D., Wegener, G. 1989. Wood-Chemistry, ultrastructure, reactions. (2. Aufl.). De Gruyter-Verlag Berlin, New York

* Liese, W. 1970. Elektronenmikroskopie des Holzes. In: H. Freund (ed.). Handbuch der Mikroskopie in der Technik. Bd. V, Teil 1: Mikroskopie des Rohholzes und der Rinden. Umschau Verlag, Frankfurt a.M.

* Ruel, K., Barnoud, F., Goring, D.A.I. 1978. Lamellation in the S2 layer of softwood tracheids as demonstrated by scanning transmission electron microscopy. Wood Sci. Technol. 12: 287-291

* Sell, J. 1994. Confirmation of a sandwich-like model of the cell wall of softwoods by light microscope. Holz Roh-Werkstoff 57: in press

* Sell, J., Zimmermann, T. 1993. Das Gefüge der Zellwandschicht S2 – Untersuchungen mit dem FE-SEM an Querbruchflächen von Fichten- und Tannenholz. Forsch. u. Arbeitsber. EMPA.-Dept. Holz, Nr. 115/28
DIFFERENCES IN PHOTOTROPIC SENSITIVITY, STEM STRAIGHTNESS AND COMPRESSION WOOD FORMATION IN *Pinus pinaster* Ait., *Pinus canariensis* Sweet. AND *Pinus nigra* Arn. SEEDLINGS

SIERRA DE GRADO, ROSARIO (*); ALÍA MIRANDA, RICARDO

*Dpto. Sistemas Forestales, C.I.T.-I.N.I.A. Ctra. de La Coruña km 7. 28040 Madrid (Spain).*
*(*) Present address: Dpto. Producción Vegetal y Ciencia Forestal. E.T.S.I. Agraria. Universidad de Lleida. Rovira Roure, 177.- 25006 Lleida (Spain).

*Pinus pinaster* Ait., *P. nigra* Arn. and *P. canariensis* Sweet. seedlings were exposed to two treatments: 1.- fixed lateral light, and 2.- alternate lateral light (monthly rotation of light incidence angle 180°). After two years of treatment in *Pinus pinaster* and *P. nigra* seedlings, and one year in *P. canariensis*, compression wood development was analyzed.

Diagrams of stems and the respective compression wood formed at several levels of the stem are presented (fig.1), showing great differences in the stem form found in the three studied species. Combinations of phototropic sensitivity, elongation rate and righting ability by formation of compression wood allow to offer an explanation to the found differences.

The vertical and straight stems exhibited by *Pinus canariensis* seedlings in comparison with the other two species, was accompanied to the limited presence of compression wood in their sections. It suggests that the form of *P. canariensis* stems were not the result of an efficient reorientation mechanism, via compression wood formation, but the consequence of weak phototropic sensitivity.

The growth rate of *Pinus nigra* seedlings was very low during the experiment, which has determined its evolution over the other involved factors.

*Pinus pinaster* seems to be the more sensitive of the three species to the lateral incidence of the light. Its sensitivity and its great elongation rate originate severe deformations in the stems, which are not compensated by compression wood formation.
<table><caption>FIGURE 1. Diagrams of stems and compression wood formed at several levels of the stem.</caption><thead><tr><th>TREATMENT 1</th><th>TREATMENT 2</th></tr></thead><tbody><tr><td><em>Pinus canariensis</em><br>light</td><td></td></tr><tr><td><em>Pinus nigra</em></td><td></td></tr><tr><td><em>Pinus pinaster</em></td><td></td></tr></tbody></table>
# KINEMATICS OF TWINING GROWTH AND MECHANICS OF THE TWINING HABIT

W.K. Silk

University of California at Davis, U.S.A.

Analysis of growth of twining vines gives a geometrical twist to problems in botanomechanics. Twining stems wind around a vertical pole to make a corkscrew-shaped form, a helical tube of tissue. The plant apex has an undulating growth trajectory, while behind the apex older tissue expands and is displaced rather smoothly through the steady form. The stem can be modelled as a tube surrounding a generative helix α(s), where s is arc length along α. Points in the stem can be given in terms of α, the Frenet vectors, and some natural coordinates. If growth velocity along α(s) is known, then a form of strain rate tensor can be used to find elongation rates of line elements through the cross-section. The continuum-mechanical analysis shows a growth rate maximum on the bottom surface of a stem which is twining clockwise and rotating counterclockwise as it elongates.

The geometry of the growth analysis also serves for mechanics of the twining habit. I hypothesize that contact forces are important in maintaining the form of the vine. An axial force within the stem should be balanced by a normal load distributed along the line of contact between stem and supporting pole. Two empirical studies verified the importance of the putative normal load. Firstly, vine geometry was measured on and off the supporting pole. When removed from the pole, the helical coil forms a coil of smaller radius, smaller wavelength, and larger torsion. Next, forces were estimated from observations of the pressure exerted by a stem twining around a water-filled balloon. The twining stem was observed to put itself into tension and to use a helical geometry to generate contact forces which are large relative to the stem weight. Most recently, the time course of development of the normal load has been determined with an electronic device, based on a thin beam load cell, which gives continuous, in situ measurement of contact loads.

## REFERENCES

* Silk, W.K. 1989 - Growth Rate Patterns which Maintain a Helical Tissue Tube. *J. Theor. Biol.*, 138: 311-327.

* Silk, W.K. and Haidar, S.A. 1986 - Growth of the stem of *Pharbitis nil*: analysis of longitudinal and radial components. *Physiol. Veg.*, 24: 109-16.

* Silk, W.K. and Hubbard, M. 1991 - Axial forces and normal distributed loads in twining stems of morning glory. *J. of Biomechanics*, 24: 599-606.
# A MECHANISTIC STUDY OF SEEDLINGS EMERGENCE FROM UNDER SUPERFICIAL OBSTACLES.

Nicole SOUTY and Colette RODE

INRA, Unité de Science du Sol, Centre de Recherches d'Avignon, BP 91, F 84143 Montfavet Cedex France.

In laboratory the emergence of seedlings was studied in relation to soil crusting and heavy obstacles independent of the underlying layer. Relationships were established between the physical and mechanical characteristics of these different obstacles and the growth force of the seedling measured previously, which made it possible to develop a predictive model of the percentage and kinetics of emergence.

If there was a crust at the surface of the seedbed, a mechanical model of rupture (bending and fracture of the crust) was assumed. It was very important to make homogeneous, continuous crusts and to repeat the same experimental conditions when measuring the resistance of the crusts and determining the experimental percentage of seedling emergence.

The crust resistances were measured with a penetrometer; the growth strengths of the seedlings (same age and issuing from calibrated seeds of same mass) and the amount of time necessary for the seedling to exert a known force, were determined by using the steel beam method adjusted in the laboratory.

The calculated probability of emergence was estimated from statistical distribution of seedling forces by using the mechanical model of rupture. There was a good agreement between this calculated curve and the observed emergence in the range of resistance of crusts from 0 to 0,8N for the sugar beet and from 0 to 3N for the maize for example. A 0.2N crust resistance allowed 100% of maize emergence and only 50% of sugar beet emergence.
The experimental maximum emergence percentages through different crusts were reached after the amount of time previously measured (with the steel beam method) increased by the amount of time necessary for the seedling to break through the crust, about 40 hours.

<figure><img src="image_152.png" /></figure>

Comparison of experimental emergence (o) with theoretical emergence (-) if bending hypothesis: a) maize, b) sugar beet.

If clods were on the surface of the seedbed, two processes could be involved in emergence: the seedling lifted the clod or it grew under the clod to escape.

The first process was independent of the surface aera; it appeared that the seedlings were able to lift obstacles the weight of which was greater than the growth force because the growing aerial part could change its shape and or move under the obstacle. To obtain the moment of the clod weight equal to the moment of the seedling force, the probability of heaving was determined after about 6 hours by using the statistical distribution of the forces developed during this period. The percentage of heaving was lower than 50 per cent when the weight of the obstacle was greater than 0.1N.

The resulting emergence percentage (heaving and escape) was greatly reduced when the seedling encountered an obstacle with a diameter greater than 3 cm.
# Mechanical Stability of Hollow Trees

Hanns-Christof Spatz

Institut für Biologie III

Schänzlestr. 1, D-79104 Freiburg i.Br.

A theoretical description for the bending stability of hollow plant stems, originally developed to describe local buckling in cereals (Spatz et al., 1990; Spatz et al., 1993) was extended to calculate the critical bending moments for a hollow elm tree as a function of the wall thickness, more exactly of the thickness of the remaining unaffected wood. Using data for "healthy" wood (Wessolly, personal communication), our computations show that buckling, as apparent from an ovalisation of the cross-section occurs to an appreciable extent only for a ratio of wall thickness/radius below 0.05 (Spatz, 1994).

Therefore, the resistance to bending moments as exerted by wind forces can for all practical cases be computed with conventional mechanics: The critical bending moment is obtained from the critical compression and the bending stiffness, i.e. the product of the second moment of area of the ring shaped cross-section and Young's modulus of elasticity in longitudinal direction. At a ratio of wall thickness/radius of 0.3 the stability is reduced to 75 % of that for a corresponding full stem, and is gradually decreased with further reduction of the wall thickness.

The mechanical properties of wood can change in various ways upon infection with different fungi (Wilcox, 1978; Schwarze, 1994). Before the stability of such trees can be assessed on the basis of theoretical considerations alone, research has to provide a much larger data base. Particularly, Young's moduli in all three directions of space and the critical compression for wood infected with fungi to various degrees need to be known.

## References:

* Spatz, H.-CH., Speck, T., and Vogellehner, D.: "Contributions to the Biomechanics of Plants. II. Stability Against Local Buckling in Hollow Plant Stems". Botanica Acta 103 (1990), 123-130.

* Spatz, H.-CH., Boomgaarden, Ch., and Speck, Th.: "Contribution to the Biomechanics of Plants. III. Experimental and Theoretical Studies of Local Buckling". Botanica Acta 106 (1993), 254-264.

* Spatz, H.-CH.: "Ein Kommentar zur mechanischen Stabilität hohler Bäume". Das Gartenamt, in press (1994).

* Schwarze, F.W.M.R., and Fink, S.: "Möglichkeiten und Grenzen von Diagnosemethoden unter besonderer Berücksichtigung des Holzzersetzungsmusters". Neue Landschaft (1994), in press.

* Wilcox, W. Wayne: "Review of Literature on the Effects of Early Stages of Decay on Wood Strength". Wood and Fiber 9 (1978), 252-257.
# Effect of branching on the internal distribution of strength within a root system.

A. Stokes & C. Mattheck

Institut für Materialforschung II
Kernforschungszentrum Karlsruhe,
Postfach 3640
76021 Karlsruhe
Germany

One of the most consistent responses of trees subjected to mechanical loading is the laying down of wood in areas of highest stress. The increase in new wood then increases the rigidity of those areas, thus reducing the stress to which they were first subjected. Hence, when applied to the whole of a tree, the tree will experience the same maximum stress all over its surface, resulting in a tree with a constant surface stress. This "constant stress hypothesis" (Metzger 1893, Mattheck 1991) would help explain the cause of localised growth in trees, such as the swelling around branch joints and buttress roots. As most trees must resist uprooting by the wind, roots must transmit bending and compression forces into the ground. If the radial growth of roots under the most stress, such as the lateral root bases, is increased, these forces will be transmitted into the soil much more smoothly. Without such an increase in woody growth, the roots might experience much larger bending forces and possibly fail under loading. As the stress decreases away from the root bases and the roots bifurcate, rigidity may also be reduced.

In order to assess how the internal distribution of strength differs within a woody root, wood samples were taken from the first and second order roots of mature beech (Fagus silvatica) and ash (Fraxinus excelsior). The beech trees examined were growing on strongly sloped ground in the Palatinian forest, whilst the ash were on flat ground in a seasonally waterlogged area of the Rhine valley (both sites in south west Germany). The samples were collected by drilling 5 mm diameter cylindrical cores through the root, at regular intervals along its length. The strength of each fresh sample was quantified by measuring the bending moment at 12 mm intervals along the length of the core, using a newly developed, pocket-size, wood-testing device (Fractometer II) (Mattheck et al. 1994). Using Fractometer II, it is possible to determine the lateral strength in the radial direction and also the "crushing" strength parallel to the fibre direction of the wood.
The highest values for lateral bending and crushing strength were found in the buttress roots of both beech and ash and reduced with decreasing root cross-sectional area (CSA) away from the stem. Regression coefficients of log<sub>strength</sub> vs. log<sub>CSA</sub> can be used to determine differences in strength between compression roots (uphill) and tension roots (downhill) in beech. It is considered how the internal strength distribution within both beech and ash roots is related to branching and whether woody growth alters in response to the local loading environment, thus reducing stress within the root.

References

Mattheck C. 1991, Trees - The mechanical design. Springer Verlag, Heidelberg, New York.

Mattheck C., Bethge K. & Zipse A. 1994, Das Fractometer. Submitted to Allgemeine Forstzeitschrift.

Metzger C. 1893, Der Wind als massgebender Faktor für das Wachstum der Baüme.
Mündener Forst Hefte, Berlin, 3:35-86.
INCREASE IN LEAF YIELD BY DWARF SHOOTS IN DENSE-PLANTED MULBERRY FIELD

Masaki Tateno

Faculty of Agriculture, Tokyo University of Agriculture and Technology, Fuchū, Tokyo 183, Japan

Present address: c/o Professor F. S. Chapin III, Department of Integrative Biology, University of California at Berkeley, Berkeley, CA 94720, U.S.A.

A shoot of mulberry tree consists of a perpendicular stem for mechanical support and leaves for assimilation. The leaves are used as feed for silkworm. Tateno and Bae (1990) defined the lodging safety factor, an indicator of mechanical stability of the shoot, as the ratio of the critical lodging load to the leaf fresh weight observed. The mulberry trees developmentally control the value of the lodging safety factor in response to the environmental condition (Tateno, 1991).

Our mechanical model based on Euler's buckling formula predicted following three: 1) When the lodging safety factor and shoot dry weight is constant, proportion of shoot dry matter partitioned into leaves increases as shoot length decreases (Fig. 1A and 1B). 2) When shoot length and shoot dry weight are constant, proportion of shoot dry matter partitioned into leaves increases as the lodging safety factor decreases (Fig. 1A). 3) When the lodging safety factor and shoot length are constant, proportion of shoot dry matter partitioned into leaves increases as shoot dry weight increases (Fig. 1B). If net shoot production per unit area remains unchanged, these increases in leaf percentage in individual shoots lead to increase in leaf production per unit area.

To examine the effect of dwarf shoots on the leaf yield per unit area, densely planted mulberry field was treated with 4000 ppm solution of succinic acid 2,2-dimethylhydrazide (SADH). SADH is a growth retardant and does not change the lodging safety factor of mulberry shoots (Tateno and Bae, 1990). We used two-year-old graftings of *Morus alba* cv Minamisakari. The shoot density was 16 per square m.

Figure 2 shows the productive structure of the untreated and SADH-treated shoots at the end of experimental period. The mean shoot length and net shoot production in the untreated plots were 1.66 m and 683 g per square m, respectively. The shoot length in the SADH-treated plots decreased by 18.7%, whereas the net shoot production was not significantly different from that in the untreated plots. In the SADH-treated plots, the trees remarkably increased the percentage of shoot dry matter partitioned into leaves. As a result, the leaf yield per unit area in the treated plots increased by 23.0%. Although this value did not precisely consist with the value predicted by the model, 29.6%, these results suggest that, in the case of dense planting, the dwarf shoots are effective for increasing the leaf yield per unit area.
References

Tateno, M. & Bae, K. (1990) Plant Physiology 92: 12-16.

Tateno, M. (1991) Physiologia Plantarum 81: 239-243.

<figure><img src="image_153.png" /></figure>

Fig. 1. A) The predicted relationship between proportion of shoot dry matter partitioned into leaves (p) and shoot length (l) assuming that the shoot dry weight (W) is 50.0 g. B) The predicted relationship between p and l on the assumption that the lodging safety factor (F) is 3.0.

<figure><img src="image_154.png" /></figure>

Fig. 2. A) Productive structure of the untreated shoots. B) Productive structure of the SADH-treated shoots. Mean of 24 shoots.
# THE EFFECT OF WIND OR GRAVITY ON WOOD FORMATION (XYLOGENESIS)

Frank W. Telewski

Assistant Professor and Curator of the W.J. Beal Botanical Garden

Department of Botany and Plant Pathology

Michigan State University

East Lansing, MI 48824 USA

Trees experience complex loading patterns involving tension, compression, torque, shear and bending, induced by a number of external mechanical stresses including wind, precipitation loading, and displacement with respect to the gravitational vector. The most obvious developmental response is the formation of reaction wood, known as tension wood in dicotyledonous woody angiosperms and compression wood in conifers.

The existence of compression wood in conifers has been recognized for over one hundred years. Its structure, function and formation have been the subject of numerous studies since the latter half of the 19th century. Numerous reviews of past research and interpretations of the collective data have been produced, most recent is the comprehensive review presented by Timell (1986,a,b,c).

Compression wood forms typically, but not exclusively, on the lower sides of branches, and leaning or crooked stems of conifers. It is characterized as being composed of tracheids which are rounded in transverse section, are shorter in length, with highly lignified secondary cell walls containing spiral cell wall checks. There is also an increase in the angle of the cellulose microfibres within the secondary cell walls of compression wood tracheids. Compression wood is usually denser and darker than normal wood with larger rays (Timell 1986a). The axial rate of cell enlargement of compression wood is greater than in normal or opposite wood. The increased elongation of the differentiating cells creates a compressive forces resulting in the righting of the stem (Timell 1986a,b,c).

Historically, wind-induced developmental responses in the tree stem have been mixed with studies on reaction wood formation and the gravitropic response (Timell 1986b,c). Under field conditions, trees exposed to strong winds tend to lean and contain reaction wood in the displaced main axis. It was not clear if the wind-induced movement of the stem induced compression wood formation in conifers or if the formation of compression wood in wind stressed conifers was the result of their displacement with regard to the gravitational vector. Wind sway is a dynamic movement of the stem creating an alternating compressive and tensile force within a vertical or displaced stem. The force of gravity, on the other hand, creates a static load on the stem with an internal compressive force on the lower side and an internal tensional force on the upper side of a displaced stem.

Telewski (1989) reported flexure stimulates wood formation and the wood shares characteristics similar to both normal and compression wood. From the perspective of design principles for biological structural systems, the structure of both compression wood and flexure wood must share some structural similarities. Purely tensile elements resist tensile forces only, whereas bending and compression elements also resist tension and shear (Wainwright et al. 1976). Compression elements need to be shorter and larger in external diameter, increasing the second moment of cross-sectional area (I), in order to withstand compression (Wainwright et al. 1976). Compression wood tracheids are consistent with this
requirement. Trees experience a complexity of loading patterns under windy conditions, including compression, tension, torque, shear and bending. Therefore, flexure wood should, and does, have some characteristics of compression elements. There is also an increase in the flexural stiffness (EI) of flexed stems. The increase is due to a significant increase in radial growth, increasing the second moment of area (I) in the direction of flexure. However, there is a decrease in the elastic modulus (E) in response to flexure. The increased I and decreased E creates a stem which is overall stiffer and more resistant to bending, but is capable of absorbing more energy as deformation of materials, a result of the lower E of the stem.

Tension wood is characterized by the presence of gelatinous fibers. These fibers have a lower lignin and higher cellulose content compared to normal fibers and create a tensional force within the stem. Very little data exists concerning the developmental anatomy of flexure wood in angiosperms and how it compares with tension wood anatomy and development. Neel & Harris (1971) observed a reduction in vessel element length and diameter in shaken *Liquidamber styraciflua* as compared to the vessel elements of untreated trees. Holbrook & Putz (1989) reported increased density (g cm⁻³) and radial growth in non-constrained (free swaying) *Liquidambar styraciflua*. As in the conifer response, this translates into a greater mass and volume of xylem produced per cm² of cambial surface area in response to flexure.

Based on the principles for biological structural systems, the tensional elements of tension wood may not be effective components within the flexure wood of woody angiosperms. A detailed comparison between tension wood and wind or flexure stimulated xylogenesis is the focus of current research.

Holbrook, N.M. & Putz, F.E. (1989). American Journal of Botany **76**, 1740-1749.

Neel, P.L. & Harris, R.W. (1971). Science **173**, 58-59.

Telewski, F.W. (1989). Tree Physiology **5**, 113-122.

Timell, T.E. (1986a). *Compression Wood In Gymnosperms, Volume I*. Springer Verlag, Berlin.

___ (1986b). *Compression Wood In Gymnosperms, Volume II*. Springer Verlag, Berlin.

___ (1986c). *Compression Wood In Gymnosperms, Volume III*. Springer Verlag, Berlin.

Wainwright, S.A., Biggs, W.D., Currey, J.D. and Gosline, J.M. (1976). *Mechanical Design in Organisms*. Princeton University, Princeton.
# Mechanical Control of Root Growth

M. Teschner, C. Mattheck

Kernforschungszentrum Karlsruhe GmbH

Institut für Materialforschung II

Postfach 3640, 76021 Karlsruhe

Federal Republic of Germany

The present paper investigates tree-root morphologies with regard to the introduction of wind loads into the soil. From the mechanical point of view the tree can be compared to a sailing ship, this means that stem, branches, roots and their joints are designed in such a way that notch stresses and waste of material are avoided. Tree roots are biological soil anchorages which fulfil the mechanical rule of biological load carriers. This is achieved by growth into a state of constant stress on the surface (constant stress axiom). The roots care for a very good anchorage of the tree in the soil with a minimum of material. Because the root-soil plate is a compound structure (root-reinforced soil) the material properties of the soil are very important. An additional difficulty is that the shear strength of the soil depends on the normal pressure on the shear lines. This is characterized by Mohr-Coulomb's law. The basic idea of this law is that the friction (shear strength) between the shear lines within the soil increases with increasing normal pressure. Therefore, there are normally more roots for soil reinforcement on the windward side where the soil is lifted than on the lee-side where it is compressed. This is the simplest example which results from Mohr-Coulomb's law. At the Karlsruhe Nuclear Research Centre the so-called SKO method was modified to predict root morphologies of trees for different loading and boundary conditions. The predictions are based on the assumption that the optimum root design (in pure mechanical sense !) is a design which guarantees an even distribution of shear stresses along the roots. This approach gives good qualitative agreement with the root formation observed in nature for cases considered here. It is clear that this mechanical optimum can be disturbed drastically by biological growth regulators as for example hydrotropism. The use of the optimization method SKO (adapted for soil problems) in the design process for technical soil anchors (foundations) leads to an increase in the loading capacity under the demand of a lightweight design.
Examples

<figure><img src="image_155.png" /></figure>

<figure><img src="image_156.png" /></figure>

FEM: M. Lumpp, J. Schäfer

Real tendril formation and SKO prediction (pipeline on the windward side)

<figure><img src="image_157.png" /></figure>

Interaction between tree roots and stones
# Measurement of transverse growth stresses in wooden disks

Rémi THOMAS, Meriem FOURNIER, Jean-Louis KERGUÈME, Bernard THIBAUT

Université Montpellier II - L.M.G.C. Bois - CP081 - Place E. Bataillon - 34095 Montpellier Cedex 5 - FRANCE

tél : (33) 6714 3483, 4739, 3431 - fax : (33) 6754 4852

Wood in standing trees is pre-stressed. These stresses originate in a physico-chemical transformation of wood at the end of its differentiation (cellular maturation). These maturation stresses (often called growth stresses) are useful for trees (they allow bending movements of reorientation or stabilization and reduce the initiation and propagation of shakes in the cambial zone). But they cause troubles during wood processing (heart shakes during felling, deformations and bad quality of sawn wood). The researches leaded in the LMGC of Montpellier aim at modelling these stresses, relating their variations to wood structure and tree growth.

The objective of our work is to validate the mechanical models. To study the stress field along the radius, an destructive experiment based on successive cuts seems necessary. This is a complement to the usual measurements of peripheral strains (Baillères 1994). Among the existing methods (Archer 1986), we have chosen to adapt the Sachs'one (1927).

This method is based on the measurements, at the periphery of a log, of the longitudinal and tangential strains induced by the drilling of successive holes (concentric and centred). These strains as interpreted as the result of the releasing of i) radial stresses of the hole surface and ii) longitudinal stresses on the transverse area supressed. This interpretation have been calculated first by Sachs (for isotropic metals), then by Doi & Kataoka 1967 (on an homogeneous circular cylindrical anisotropic log) and Sasaki & al 1981 (radially unhomogeneous cylindar).

First, we have chosen to implement the experiment on disks (rather than logs). Thus, only the transverse stresses can be valued. The Sachs'calculations have been modified to account for plane stresses, in a very thin, cylindrical orthotropic homogeneous disk. The tangential strain εθ at the disk surface is :

$$γ^2 = \frac{K_{22}}{K_{11}}$$

$$ε_θ = (AR_fγ^{-1} + BR_fγ^{-1}).σ_π^o(R) \text{ with } A = \frac{K_{11}γ - K_{12}}{K_{11}γ + K_{12}}Rf^{-2γ}$$

$$B = \frac{K_{11}γ - K_{12}}{(-K_{11}γ + K_{12})^2 Rγ^{-1}Rf^{-2γ} - (K_{11}γ + K_{12})^2 Rγ^{-1}}$$

$$\text{where } K_{11} = C_{11} - C_{13}^2 / C_{33}; \quad K_{22} = C_{22} - C_{23}^2 / C_{33} \text{ et } K_{12} = K_{21} = C_{12} - C_{13}C_{23} / C_{33}$$

(Cij : elastic compliances, Rf : disk radius, R : radius of the drilled hole, σ°π(R) : radial stress released by drilling).

The diameter variation Δφ also allows to estimate σ°π(R) since Δφ/φ = εθ.

The compliances Cij will be calculated from the specific density of wood using Guitard's models for air-dried wood corrected for green wood (Fournier 1989). Simulations have been done, assuming that $σ°π(R) = -\hat{σ}_θ\text{Log}R/R_f$ (Kübler's model).

Experimentally, the disk (≈1cm thick) is prepared with a bandsaw (and a special truck) and put on a hard and smooth bearer (disk of teflon) in order to minimise the risk of adherence. Then, it is necessary to clamp the disk (two opposite tightening points of are sufficient) against cutting forces. Lastly, contrary to what is usually done, the cutting and feeding speeds Vc and Vf are taken very low (Vc≈6,5m/mn; Vf≈0,01mm/tooth) to avoid vibrations. Moreover, four extensometers (using electric strain gages, H.B.M. type DD1) are nailed (using compasses points) tangentially around the disk, two displacement sensors (Mitutoyo 543) allows to measure the variations of diameter.diamétralement opposés. For each drilled hole, measurements are done after tightening, after drilling, and after loosening.
Figure 1 shows the experimental apparatus and figure 2 an example of results obtained on a disk of poplar I-214. Observed results are slightly lower than theoretical calculations, which can be explained by a partial recovery of locked-in strains during disk conservation.

This experimental device is now operational to evaluate transversal stresses in disks. The aim is to use it to study the variability of these stresses in different species, for different histories of growth, and relate the results to longitudinal strains measured at the stem surface in the standing trees. It will be also used to study the relaxation of stresses with time, temperature, etc. Improvements are planned in the theoretical calculations to take into account asymmetries often observed (eccentricity of the pith, circumferential heterogeneities). Lastly, we will try to develop the same experiment on logs (that will allow also the measurements of longitudinal strains).

## References

* Archer R. (1986) "Growth stresses and strains in trees". Springer Series in Wood Science. Ed. E. Timell, Springer Verlag

* Baillères H. (1994) "Précontraintes de croissance et propriétés mécanophysiques de clones d'Eucalyptus (Pointe Noire - Congo) : hétérogénéités, corrélations et interprétations histologiques". Thèse de l'Université de Bordeaux 1

* Fournier M. (1989) "Mécanique de l'arbre sur pied : maturation, poids propre, contraintes climatiques dans la tige standard." Thèse de l'INPL, Nancy

* Kubler H. (1959a) "Stües on growth stresses in trees. 1. The origin of growth stresses and the stresses in transverse direction." Holz als Roh und Werkstoff 17(1) 1-9. In German

* Sachs G. (1927) Zeitschrift für Metalkunde 19 352-357.

* Sasaki Y., Okuyama T. & Kikata Y. (1981) "Determination of the Residual Stress in a Cylinder of Inhomogeneous Anisotropic Material I & II". Mokuzai Gakkaishi vol.27 n°4 : 270-282.

<figure><img src="image_158.png" /><figcaption>fig 1 : Practical Application</figcaption></figure>

<caption>fig 2 : Experimente Results</caption>
WATER RELATIONS OF ROOT GROWTH OF PINUS PINASTER
AT SINGLE-CELL LEVEL

Marie-Béatrice Triboulot¹, Jeremy Pritchard² and Deri Tomos²

¹: INRA, Laboratoire Sol et Nutrition, Route d'Amance, 54280 CHAMPENOUX.
Tel: 83-39-40-41, Fax: 83-39-40-69.

²: School of Biological Sciences, UCNW Bangor, Gwynedd LL57 2UW, Wales, UK.
Tel: (0)248-351151, Fax: (0)248-370731.

The ability to maintain root growth in a drying soil is considered an adaptation to drought. A continuation of root growth allows an exploitation of a larger volume of soil. Root growth is the consequence of the elongation of the cells produced by the meristem situated in the tip of the root. When water is not limiting the control of the expansion of cells can be summarized by this equation (1) :

$$r = \phi (P-Y)$$

where r = expansion rate, φ = cell wall extensibility, Y = yield threshold and P = turgor pressure. φ and Y are the rheological cell wall properties. The cell turgor is dependant of the cell sap osmotic pressure (π). Bulk measurments of P and π will obscure a cell-to-cell heterogeneity within a root. The cell pressure probe and the picoliter osmometer (2) have been used to study the water relations of the root of seedlings of maritime pine, Pinus pinaster, at the single-cell level in well watered conditions and at two levels of osmotic stress.

P and π were measured in the first root of 2-week old pines grown in hydroponics. The local growth rate of the root tip was determined from the cell length profile along the root apex (3). Figure 1 shows that the elongation zone expands over the first 8 mm.

<figure><img src="image_159.png" /><figcaption>Fig. 1: Local growth rate, turgor (●) and osmotic pressure (▲) along the root apex. Turgor: single cell measurements. Osmotic pressure: samples pooling 2-3 cells, means ± s.d., n = 4. Local growth rate: means ± s.d., n = 9.</figcaption></figure>
Despite the large changes in growth the turgor pressure was constant at about 0.5 MPa along the apical 16 mm. According to the equation the constant turgor along the growing zone implies a modification of the rheological properties. The walls must loosen in the apical part of the expanding zone (as r increases) and tighten in the distal part (as r decreases). The osmotic pressure of the vacuole sap was also constant over the apical region but higher than was P, by about 0.7 MPa. So the water potential of the cell was -0.2 MPa but the root bathing medium water potential was only -0.05 MPa. The presence of solutes in the apoplast may provide an explanation for the lower water potential than these of the nutrient solution.

Two levels of osmotic stress have been applied by adding polyethylenglycol (M = 3500 g/mol) to the nutrient solution. After a 3-day adaptation period the seedlings showed a stable growth rate.

<figure><img src="image_160.png" /><figcaption>Fig. 2 : (a) Growth rate of the first root for the control and the two osmotically stressed treatments. Means ± s.e., n = 24. (b) Local growth rate along the root apex for the three treatments. Means ± s.d., n = 6.</figcaption></figure>

Surprisingly a moderate osmotic stress (0.3 MPa) increased the root growth rate whereas a more severe stress (1.2 MPa) decreased it (fig. 2a). The local growth rate for the three treatments is given in figure 2b. The moderate osmotic stress induced an increase of the local growth rate all over the growing zone but the strong one decreased it and shortened the elongation zone. This might imply that the growth rate increase was governed by a different mechanism than the decrease. This hypothesis is being tested by measuring P and π of individual cells along the expanding zone as the root grows under both moderate and severe stresses.

References :

(1) : Lockhart J.A. (1965), *J. Theoret. Biol.* **8** 264-275.

(2) : Tomos et al. (1994), in *Plant cell biology - A practical approach*. (eds. N. Harris and K.J. Oparka) IRL Press, Oxford (in press).

(3) : Silk et al. (1989), *Plant Physiol.* **90** 708-713.
Influence of Global Shape and Internal Structure of the Tomato on the Reliability of Firmness Estimation by the Acoustic Impulse Response Technique

Xavier Vandewalle,
Jan Langenakens,
Josse De Baerdemaeker,
Department of Agricultural Engineering, Katholieke Universiteit Leuven
Kardinaal Mercierlaan 92, 3001 Heverlee, Belgium

The firmness of a tomato is becoming one of the main characteristics on which it is classified in different classes of quality. Recently a non-destructive acoustic response technique, based on resonance frequencies, has been under development. The measurements are conducted by monitoring the response of the tomato which is excited by impact. The response is captured by a small microphone. This method allows to monitor the firmness evolution of tomatoes during storage or on the plant to estimate the optimal time of harvesting. The technique has application possibilities to be implemented in sorting lines for grading or to be used as an objective tool to check the initial quality of the fruit at the auctions. So far, little is known about the sensitivity of the method to non-regular fruit shapes and to internal structure.

Tomatoes of different sizes, shapes and maturity stages were tested with the experimental modal analysis technique. Modal analysis is a technique applied in vibration analysis to describe the dynamic behaviour of mechanical structures. The modal analysis theory shows that this dynamic behaviour depends on the modal parameters such as the resonance frequencies of the system, damping factors and mode shapes (deformation shapes at the resonance frequencies). The modal parameters are estimated through frequency response function (FRF) measurements. An FRF is the ratio between the output (acceleration) and the corresponding input (force) as a function of the frequency. For describing the system dynamics at least the measurements of the FRF between the response location and the force positions of interest are necessary. The second step, modal parameter estimation, fits an analytical expression to the measurements, describing the FRF's in terms of the modal parameters. The resulting modal model is useful in further analysis as vibration trouble shooting, sensitivity analysis and others. In the modal analysis here the tomatoes are excited with a small impact hammer instrumented with a force cell and the response is measured with a small accelerometer which was attached to the tomato surface. Measurements and analysis were performed with LMS CADA-X software on HP 715 workstation combined with a DIFA-SCADAS II data acquisition system.

Analysis results show that the resonance frequencies can be accurately measured by a microphone. Secondly, the first mode shape, which is most conveniently used to estimate the firmness, is an 'oblate-prolate' shape (Figure 1). This mode shape has the largest deformations at the equator of the tomato. This fact implies that the best positions for measuring and impacting are located on the equator and 180° from each other. Taking these considerations into account, no significant difference between spherical and non-
spherical tomatoes was found.

The influence of internal compartment structures on the resonance frequencies was also studied. No meaningful differences could be found between frequencies, measured on locations of juicy parts as on flesh or wall constructions. While maturing, tomatoes get more soft. This effect can be monitored by the acoustic impulse response technique. The resonance frequency of all the mode shapes decreases gradually.

The modal analysis was an important step in setting up the testing procedure for the evaluation of the tomato firmness on the basis of its resonance frequency. Using the acoustic impulse response technique, this can be very easily used in practice to estimate tomato quality. The results of the research presented here show the method not to be sensitive to the global shape and internal structure of the tomato.

<figure><img src="image_161.png" /><figcaption>Figure 1: First mode shape of a non-spherical tomato (±260 Hz)</figcaption></figure>
# Biomechanical properties of *Cyclamen persicum* MILL. flower stalks

Julia Vocke und Thomas Speck

Botanic Garden of the Albert-Ludwigs-University
Schänzlestr. 1, D-79104 Freiburg, Germany

Four cultivars of *Cyclamen persicum* with - in fully bloomed condition - different length and diameter of flower stalks have been investigated with regard to their biomechanical properties. In order to test, if the biomechanical properties change in the course of the ontogeny, flower stalks of each cultivar, in different developmental stages were experimentally studied. For characterization of the biomechanical properties, the following parameters have been determined quantitatively: 1.) tapering mode of the flower stalks, 2.) specific gravity of the flower stalks, 3.) flexural stiffness and Young's modulus of the flower stalks, 4.) weight of the flower bud respectively the flower.

1.) Tapering mode of the flower stalks: the vertical part of the flower stalks - i.e. the flower stalk section between the short, bent, in direction to the bulb conically tapering basic part and the short, apical section bent in form of a hook where the flower is attached - can best be described as a rotation paraboloid of 2. order (tapering mode: n = 0.5) for all cultivars and all ontogenetic stages (see figures).

<figure><img src="image_162.png" /></figure>

2. Specific gravity of the flower stalks: the specific gravity of freshly gathered flower stalks does not differ significantly between the different ontogenetic stages neither of a single cultivar nor if combined for all four tested *Cyclamen persicum* cultivars (see table 1 & 2; average specific gravity of all tested flower stalks: γ = 10.0 ± 0.9 [kNm⁻³], n = 65).
3.) Young's modulus of the flower stalks: The Young's modulus (E) of the straight part of the flower stalks have been measured by 3-point-bending with discret increase of the bending weight forces. Young's modulus had been determined for different ontogenetic stages of freshly gathered flower stalks of the four tested *Cyclamen persicum* cultivars, grown in water saturated soil (water potential of the stalks: -0.15 [MPa] < ψ < -0.47 [MPa], mean value ψ = -0.33 ± 0.01 [MPa]). The Young's moduli greatly vary within the different tested cultivars as well as within the different ontogenetic stages (11 [MNm²] < E < 120 [MNm²]). Statistical tests show, that only flower stalks of the oldest studied ontogenetic stage - i.e. flower stalks with fully bloomed flowers - differ significantly from the other ontogenetic stages, having significantly higher Young's moduli as flower stalks of younger ontogenetic stages (see table 1). This is due to the increasing amount of collenchymatous respectively thick-walled parenchymatous cells in the stalks periphery found in the oldest ontogenetic stage.

4.) Weight of flower bud respectively the flower: The weight of the flower bud respectively the flower increases more or less continuously from the early bud phase until the stage of fully bloomed flowers in the four investigated cultivars of *Cyclamen persicum* (the weight of the flower reaches during ontogeny about three- to fourfold its initial value).

These parameters allow to calculate the safety factor (s) of the flower stalks against failure by global buckling. These safety factors can be calculated as a quotient of the critical buckling length and the real length of the investigated stalk. The safety factor (s) means, that a stalk could be s-times longer until it would fail by global buckling due to the load produced by the weight of the stalk itself which is continuously distributed along its length and by the apical weight of the flower. All investigated *Cyclamen persicum* cultivars showed a decrease of the safety factors during the ontogeny of the flower stalks. The safety factors decrease from average s = 2.9 in the youngest studied ontogenetic stages to s = 1.8 in the oldest testet ontogenetic stages, i.e. of flower stalks with fully bloomed flowers. This finding may be correlated with the mode of seed dispersal in *Cyclamen*. The safety factors will be experimentally checked by loading the flower stalks with additional loads.

<table><caption>Table 1: Mean values of all tested cultivars (n = number of measurements)</caption><thead><tr><td></td><td>specific gravity [kNm<sup>-3</sup>]</td><td>Young's modulus [MNm<sup>-2</sup>]</td></tr></thead><tbody><tr><td>Ontogenetic stage 1</td><td>9.8 ± 0.8 (n = 12)</td><td>34.5 ± 13.5 (n = 13)</td></tr><tr><td>Ontogenetic stage 2</td><td>10.1 ± 1.1 (n = 13)</td><td>37.4 ± 16.1 (n = 12)</td></tr><tr><td>Ontogenetic stage 3</td><td>10.0 ± 0.9 (n = 14)</td><td>40.5 ± 19.3 (n = 17)</td></tr><tr><td>Ontogenetic stage 4</td><td>10.1 ± 0.9 (n = 26)</td><td>70.0 ± 23.2 (n = 20)</td></tr></tbody></table>

<table><caption>Table 2: Mean values of the specific gravity of all ontogenetic stages</caption><tr><td>'Giganteum Turbo'</td><td>10.6 ± 0.5 kNm<sup>-3</sup> (n = 11)</td></tr><tr><td>'Scholten'</td><td>10.2 ± 0.9 kNm<sup>-3</sup> (n = 20)</td></tr><tr><td>'Miniatur Anglia'</td><td>9.8 ± 0.8 kNm<sup>-3</sup> (n = 21)</td></tr><tr><td>'Miniatur Pinokkio'</td><td>9.7 ± 1.2 kNm<sup>-3</sup> (n = 13)</td></tr></table>

## Literature:

Dierks, K., Hafner, L., Tietge, H.-W. & Wenderling, R. (1986): Zum Tragverhalten des Alpenveilchens. - Symposium on Cellular Mechanics, Konzepte SFB 230, Heft 18: 25-29.

Niklas, K.J. (1992): Plant biomechanics. University of Chicago Press, Chicago.

- (1994): The allometry of safety-factors for plant height. - Am. J. Bot., 81: 345-351.
# THE MECHANICAL EFFICIENCY OF BAMBOO AND PALM

U.G.K. Wegst, H.R. Sherciff and M.F. Ashby
University of Cambridge, Department of Engineering,
Trumpington Street, Cambridge, CB2 1PZ, U.K.

It is well known that the natural materials bamboo and palm have a good specific stiffness in bending, and also resist buckling under their own weight. These properties are exploited in engineering design using bamboo. Microscopical examinations have been conducted to reveal the key features of the structure of bamboo and palm from an engineering standpoint. These show that: (i) both materials are composites of two components, i.e. bamboo and palm are fibre composites in which the fibres are aligned with the longitudinal axis of the culm or petiole respectively; (ii) the materials have a density and modulus gradient across the section, (iii) the composite material is disposed in an overall shape, such as a hollow tube (e.g. bamboo), or a tube with a low density core and a dense, stiff wall (e.g. palm) (Figures 1& 2).

The structural efficiency of bamboo, palm and other light, stiff natural materials may be evaluated using the Cambridge Materials Selector (CMS) software package, which is based on *material property charts*. These show, for example, Young's modulus *E* against density *ρ*, as in Figure 3. Engineering performance is captured by an appropriate *merit index*, a combination of material properties which need to be maximised to maximise performance (e.g. the lightest beam of a given stiffness is the one with the maximum value of *E*¹/²/ρ). Figure 3 shows the line *E*¹/²/ρ = constant, for bamboo: materials above the line give better performance in bending than bamboo; those below (including many common engineering materials) are less effective.

Further bending efficiency is obtained by disposing the material in an overall shape such as a tube. This may be described by a *shape factor*, which measures the gain obtained in flexural rigidity (at constant mass) by shaping the material, relative to a solid cylinder. The radial gradient in modulus in palm and bamboo gives a small additional shape factor of, at most, 1.5 (Gibson *et al.*, 1994). Figure 4 tabulates shape factors for structural natural and engineering materials, with the modified merit index for bending (ΦE)¹/²/ρ including shape. Bamboo in its natural tubular state still performs very well in bending compared to the much thinner tubes which can be made with engineering materials.

This approach allows conclusions to be drawn on the structural optimisation found in natural materials, how these may be exploited in engineering design and how the underlying principles may be employed in the development of new materials.

## References

1. M.F. Ashby (1992), *Materials Selection in Mechanical Design*, Pergamon Press, Oxford.

2. M.F. Ashby, L.J. Gibson, U.G.K. Wegst and R. Olive (1994), The mechanical properties of natural materials I: Material property charts, to appear in *Proc. Roy. Soc. A*.

3. L.J. Gibson, M.F. Ashby, G.N. Karam, U.G.K. Wegst and H.R. Sherciff (1994), The mechanical properties of natural materials II: Microstructures for mechanical efficiency, to appear in *Proc. Roy. Soc. A*.
<figure><img src="image_163.png" /><figcaption>Figure 1: Micrograph of a cross-section of bamboo culm wall.</figcaption></figure>

<figure><img src="image_164.png" /><figcaption>Figure 2: Micrograph of a cross-section of a palm petiole (Chamaerops humillis).</figcaption></figure>

<figure><img src="image_165.png" /><figcaption>Figure 3: The Young's modulus E - density ρ chart for natural and engineering materials.</figcaption></figure>

<table><caption>Figure 4: Shape factors and merit indices for bending for natural and engineering materials.</caption><thead><tr><th rowspan="2">MATERIAL</th><th>E</th><th>ρ</th><th>Shape factor</th><th>E<sup>1/2</sup>/ρ</th><th>(ΦE)<sup>1/2</sup>/ρ</th></tr><tr><th>GPa</th><th>Mg/m<sup>3</sup></th><th>Φ</th><th>GPa<sup>1/2</sup>/(Mg/m<sup>3</sup>)</th><th>GPa<sup>1/2</sup>/(Mg/m<sup>3</sup>)</th></tr></thead><tbody><tr><td>Balsa (MD)</td><td>4.0</td><td>0.2</td><td>4.0</td><td>10.0</td><td>20.0</td></tr><tr><td>Oak</td><td>11.5</td><td>0.7</td><td>4.0</td><td>4.8</td><td>9.7</td></tr><tr><td>Pine</td><td>11.0</td><td>0.5</td><td>4.0</td><td>6.3</td><td>12.5</td></tr><tr><td>Bamboo</td><td>22.5</td><td>0.75</td><td>7.5</td><td>6.3</td><td>17.3</td></tr><tr><td>CFRP unidirectional</td><td>160.0</td><td>1.5</td><td>15.0</td><td>8.4</td><td>32.7</td></tr><tr><td>CFRP laminate</td><td>45.0</td><td>1.5</td><td>12.0</td><td>4.5</td><td>15.5</td></tr><tr><td>Aluminium alloys</td><td>75.0</td><td>2.8</td><td>40.0</td><td>3.1</td><td>19.6</td></tr><tr><td>Steels</td><td>210.0</td><td>7.9</td><td>40.0</td><td>1.8</td><td>11.6</td></tr></tbody></table>
## Two methods to measure the strength and stability of trees

Dr. Ing. Lothar Wessolly
Institut für BaumDiagnose
Gerokstaffel 1
D-70184 Stuttgart
Allemagne

Trees are an indispensable part of town planning. However, They compete continuously with others using the same site. As a result, a tree can suffer a variety of injuries which transform it into an unsuspected danger. Internal rotting in the part above ground or in the roots may have reduced its stability to such an extent that the tree could break or uproot. The sudden exposure of a tree which was previously sheltered may lead to excessive loads which can turn into a hazard.

Within the framework of a research project carried out at the University of Stuttgart, methods began to be developed in 1986 to determine the stability of trees without destroying them. This non-destructive process was an important aim since any investigation involving destruction leads to subsequent damage and reduces stability still further. In engineering, it is standard practice to carry out an individual structural analysis of the object in question. The loads, the loaded structure and the materials involved are analysed as one unit.

In the statics of trees, we distinguish two basic types of failure: uprooting and breaking. In the former case, the roots are levered out of the ground, in the latter case, the tree above ground breaks under excessive bending pressure.

Neither of these two types of failure can be predicted theoretically. The missing values have to be ascertained for each individual tree. In order to investigate the anchoring, the stability, the inclino-method was developed in practical experiments. Following the determination of the size of the crown and the analysis of the prospective loading during hurricane winds by means of computer graphics, the tree is subjected to a wind-equivalent load using a rope winch or similar method. This load is measured. Simultaneously, the resulting inclination is measured between the bases of the main roots with an inclinometer. Measurements taken on more than 1000 trees situated in towns and parks have revealed a tilding behaviour, described in a generalised tilt curve. The tild mechanics of trees has thus become clear for the first time. In the case of normal soils, the force can be increased to an inclination of only about 2,5 - 3 degrees. In then remains constant, falling again for higher inclinations in dependence of the quality of the anchoring. A knowledge of this generalised tilt curve allows the prediction of the expected tilt load in the case of destruction-free inclinations below 0,5 degrees. With a comparison of the loading analysed for hurricane conditions, the stability of a tree can be stated explicitly without digging up the roots. No other method of analysing the stability than that using the difference in inclinations is as yet known.

The analysis of fracture limits also uses methods from experimental mechanics and is based on the following: during bending, the wood fibres are loaded in cross-section depending on their position. The further they are towards the centre of the trunk, the less significant they are for the statics. Thus, the wood fibre subject to the highest loading is always directly beneath the bark. The loading is evident in the strain. We have now discovered that the bark undergoes this strain process without resistance. This means that, if two needles are fixed vertically at a distance in the bark, their relative displacement under a bending load can be
measured. This measurement is thus also carried out without destruction of the tree and allows the investigation of any number of areas on it. We have mentioned the special strain measurement device, the **elastometer**. For this investigation, the crown of the tree is subjected to forces. The elastometer is moved vertically over an area of suspected rotting until the weakest point has been found, this being the point with the greatest strain value. A comparison of the wind-equivalent load and the load for hurricane conditions yields the strain in the case of hurricane. We now compare whether or not this strain exceeds the limit value for the specific type of wood in a hurricane. The limit value is defined as the point at which a load increase causes plastic deformation in the compression zone. A subsequent failure is determined by secondary processes and is not directly connected with this primary failure. The limit values for green wood in the case of short-term loading, as in a storm, are recorded in the "Stuttgart Strength Catalogue". With the elasto-method, the fracture point and fracture limit value can be determined in a closed system integrally and without causing damage. The validity of this procedure has been proven in numerous experiments.

Moreover, growth stresses in trees an the response of trees in storms can also be measured with the **elastometer**. Long-term observations of damage caused by fungus are naturally also possible on a living tree.

As a reinforcement of the load analysis, storm-load investigations of trees are being carried out with the aforementioned mobile measuring devices in northern Corsica. The measurements are taken with respect to time: how high is the maximum loading of a tree during a particular hurricane period ? In this way, it is unnecessary to analyse each movement of the tree and each storm eddy. The drag coefficient of trees in hurricane conditions is between cw = 0,1 and 0,35.

Both the elasto- and the inclino-method - which can be applied simultaneously - represent well-tested techniques which have considerably extended the possibilities for tree diagnosis in a safety context and opened new areas of research.
# Towards an understanding of the mechanical behaviour of cereal crops

Ethel M. White

Department of Agriculture for Northern Ireland, Plant Testing Station, Crossnacreevy, Castlereagh, Belfast BT6 9SH

Crops of the temperate cereals - wheat, barley and oats - are somewhat artificial because they are monocultures of genetically identical plants. They are also managed 'to the limit' in Western Europe where growers' objectives have been, until recently, to produce maximum yields by maximising the quantity of N fertiliser applied and using plant growth regulators to reduce lodging. This has put a strain on both breeders and agronomists in their endeavours to improve productivity and at the same time to minimise problems associated with damage due to lodging. Whilst their efforts have been successful in that very high yielding crops can be grown without problems associated with straw damage, we have still some way to go in our understanding of the phenomenon of lodging.

In this paper, the structure of the cereal plant will be examined from a mechanical perspective and the characteristics contributing to the plant's mechanical behaviour will be identified. The influence of agronomic factors on these characteristics will be discussed, using results from experiments conducted on winter wheat and winter barley in Northern Ireland.

The type of damage described as lodging will be considered in relation to 'synoptic' mechanical behaviour of the crop. Lodging is generally considered to be a catastrophic event resulting from failure somewhere in the shoot/root/soil system. The various theories about the mode of failure will be discussed and alternatives presented and explored.

Finally, the nature of crop management will be taken into account in a consideration of strategies which can be developed to limit and control damage due to lodging.
# THE EFFECT OF MOISTURE CONTENT ON THE MECHANICAL PROPERTIES OF A SEED SHELL

Lisa WILLIAMSON and Peter LUCAS

Department of Anatomy, University of Hong Kong
Li Shu Fan Building, 5 Sassoon Road, HONG KONG

A seed contains the embryo - a potential member of the next generation of a species - and its food store. The latter is an attraction for seed predators. Most seeds are heavily protected from predation by chemical or mechanical means. Many seeds, though not normally those species from tropical rainforests, can survive a considerable reduction in their moisture content and reduce their metabolic activity to a very low (dormant) level.

The mechanical properties of the seed shells of the African mongongo nut, *Schinziophyton rauteneii* (Euphorbiaceae), were measured by compressive C-ring tests while they were avi-dry and also after soaking in distilled water. Young's modulus was about 5 GPa and fracture strength was 45-50 MPa, for both conditions. However, fracture toughness was affected significantly by moisture content. The critical stress intensity factor (Kic) of air-dry specimens was 27% greater and the work of fracture (R) 69% greater than those of wet specimens. This difference corresponded well with microscopic observations of the complexity of the fracture surface. Viewed either by scanning electron microscopy or confocal microscopy, cracks in wet shell deviated neatly around individual fibres while cracks in air-dry shells either crossed individual fibres or ran obliquely across the outer layers of the secondary cell wall leaving a feathered appearance. It is proposed that the increase in toughness of shells which would be obtained from air-drying may help protect embryonic seed tissues from predation by larger animals (e.g. vertebrates such as rodents) after abscission from the parent plant. These seeds can then lie on the ground or in the soil as a "seed bank".

In the effect on toughness that we have demonstrated were to be general, then the outer protective layer of such seeds, nearly always a thick-walled dead tissue -a "pallisade" fence-like tissue if not truly fibrous, would act more efficiently after air-dryin. This would be expected to reduce the rate of seed loss to predators, particularly from those predators large enough for crack propagation between cells to be a factor. These would include many mammals, typically rodents which specialise on dry fruits, but also peccaries and some human groups. The effectiveness of the fruit pod (a dry type of pericarp which protects orthodox seeds in, for example, legumes) may also be enhanced by drying. Some seed predators, particularly primates like new and old world monkeys and also apes, tend to eat unripe seeds. The need to attack the seed while the toughness of the seed coat or shell is still low may play some part in this decision. Germination of a seed follows a period of water uptake. An increase in water content would decrease the toughness of protective tissues. However, this reduction in toughness is probably necessary if germination is dependent on turgor pressure to open the shell. Mechanical protection is obviously ruled out at this stage.

Many thanks to Charles R. Peters for providing mongongo nuts that he collected. This study was supported by grants CRCG 337/031/0015 from the University of Hong Kong and RGC HKU324/93M from the Research Grants Council of Hong Kong.
# Axial alteration of stem and leaf sheaths stiffness in cereal plants as revealed using an ultrasonic method

Jacek Żebrowski

Plant Breeding and Acclimatization Institute
Radzików, POB 1019, PL-00-950 Warsaw, Poland

Stems tapered accropetally, the presence of leaf sheaths enforcing lower parts of internodes and peripheral location of sclerenchyma on cross-section are the most striking features of cereal plant shoots related to their mechanical function as beam structures. Material properties of the shoots have been determined as averaged over whole length of the internodes and the leaf sheaths (Hozyo and Oda, 1965; Niklas, 1990). The present study investigates the alteration of stiffness within particular internodes and leaf sheaths in four species of cereals at two stages of their development.

## MATERIALS AND METHODS

Plants of rye, triticale, wheat and barley were harvested at heading and milk maturity. The stiffness was examined in c. 3 cm long sections of internodes and separated leaf sheaths by means of a through-transmission ultrasonic method based on propagating the longitudinal waves of the frequency of 100 kHz in axial direction of the specimens. The specific dynamic modulus of elasticity calculated as the squared ultrasound velocity was a measure of the stiffness. The ultrasonic measurements were performed using a concrete tester (model CT1, UNIPAN, Poland) interfaced with a computer.

## RESULTS

The measurements of the ultrasound velocity revealed considerable alteration of the stiffness within particular internodes and leaf sheaths that follows pattern similar for all tested species of cereals. Much more pronounced heterogeneity in the material properties within the internodes was observed at heading (Fig. 1), when the stems still elongate, in comparison to that at the stage of milk maturity (Fig. 2), when the development of all tissues was completed. Local reduction in the stiffness from values ranging from 2 to 8 MPa m³ kg⁻¹ typical for mature sections to values much below 0.1 MPa m³ kg⁻¹ in elongating zones made the stems at heading structures instable even under their own weight. The leaf sheaths, which protect the elongating zones and reinforce the shoots exhibited the stiffness increasing basipetally, in the direction of increasing flexibility of the internodes (Fig. 1). In fully developed stems at milk maturity the stiffness was distributed rather uniformly along whole its length with local maxima occurring at mid parts of the internodes. Relatively taller plants of rye and triticale exhibited higher values and more pronounced alteration of the stiffness within both the internodes and the leaf sheaths in comparison to wheat and barley. The local variations of the stiffness were found to coincide, generally, with the alterations of the second moment of inertia.

The present studies indicate that the vertical alteration in the material properties results not only from the intercalar pattern of the shoot growth but also has some functional significance with respect to the mechanics of cereal plants.
<figure><img src="image_166.png" /><figcaption>Fig. 1. Schematic presentation of a typical pattern of stiffness alteration in stem (solid line) and leaf sheaths (dashed line) along shoot axis in cereal plants at heading. The stiffness, determined using an ultrasound velocity method, is given in relative values.</figcaption></figure>

<figure><img src="image_167.png" /><figcaption>Fig. 2. Schematic presentation of a typical pattern of stem stiffness alteration along shoot axis in cereal plants at the stage of milk maturity. The stiffness, determined by means of the ultrasound velocity measurements, is given in relative values.</figcaption></figure>

REFERENCES

Hozyo Y., Oda K. (1965) Jap. J. Crop Sci. 33: 263-267

Niklas K.J. (1990) Ann. Bot. 19: 962-966
# Déformations du fût et fibre torse chez l'épicéa (Picea abies Karst.)

Dr. Ernst Zürcher

Prof.Dr. Ladislav J. Kucera

Matthias Brunner

Ecole Polytechnique Fédérale de Zürich, Département de Recherche sur les Forêts et le Bois, Chaire des Sciences du Bois, ETH-Zentrum, CH-8092 Zürich.

## Résumé

Les déformations du fût, provoquées par une irrégularité des cernes d'accroissement, ainsi que la fibre torse (forte déviation des éléments du xylème par rapport à l'axe de la tige) provoquent une importante diminution de la qualité et de la valeur du bois. Ces anomalies de croissance sont notamment à l'origine d'un comportement au séchage irrégulier (gauchissement) et d'une réduction de la résistance à la flexion.

Ces particularités de la formation du bois ont connu récemment un regain d'intérêt, notamment en relation avec la thèse selon laquelle elles représenteraient sous cette forme un phénomène nouveau, à tendance croissante au courant de la dernière décennie.

Par l'étude de l'anatomie et de la morphologie d'un groupe d'arbres particulièrement atteints, ce travail cherche d'une part à distinguer clairement chacune de ces deux particularités de croissance. D'autre part, il détermine à partir de quelle année on peut respectivement les observer, en essayant d'établir la relation avec des interventions sylvicoles notifiées depuis l'année 1926.

Il en ressort les résultats principaux suivants:

- la densité des rayons médullaires, leur hauteur, le diamètre des canaux résinifères et leur enveloppe épithéliale varient selon qu'ils soient mesurés dans des cernes annuels réguliers (normaux) ou irréguliers (provoquant des déformations du fût),

- dans les zones de fût excentriques, la proportion de bois de réaction est supérieure sur le grand rayon, intermédiaire sur le rayon nord et minimale sur le petit rayon,

- l'excentricité est orientée selon l'axe sud-ouest (petit rayon) - nord-est (grand rayon),

- le degré de déformation du fût (cannelures) décroît rapidement de bas en haut dans les deux premiers mètres,

- chez les arbres de la strate dominante (à fortes déformations), les cernes irréguliers apparaissent presque simultanément durant les années 1964-1967,

- à partir de cette époque et surtout dans les dernières années ( périphérie), les parties de cernes hypertrophiées sont placées sur les cernes successifs selon un mouvement centrifuge en sens généralement inverse de la rotation des aiguilles de montre - ce phénomène est décrit pour la première fois ici, et se place probablement sous le principe de la spiralité régissant les végétaux dans différents niveaux de structure,
- la déviation des fibres à la surface du fût par rapport à l'axe est maximale sur les faces est et nord,

- la fibre torse orientée vers la gauche est trois fois plus fréquente que celle orientée vers la droite,

- la fente de rondelles selon les quatre directions cardinales confirme la formation de fibre torse orientée systématiquement à gauche dès les premières années, et ceci indépendamment de l'apparition ultérieure de cernes irréguliers,

- sur les grands rayons des rondelles excentriques, la part de fibre torse orientée à droite est supérieure à celle observée sur les petits rayons,

- la déviation des fibres par rapport à l'axe est donc un phénomène distinct et indépendant de déformations apparaissant sur la surface du fût.
Biomécanique des végétaux
*Plant biomechanics*

<figure><img src="image_168.png" /></figure>

EXPOSES INVITES - *INVITED TALKS*

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Volume 2, Number 2

Special Issue:
Plant Biomechanics Congress

June 1994

BIMIEL 2(2) 77-192 (1994)

ISSN 1059-0153

Biomimetics

PLENUM PRESS • New York and London
# BIOMIMETICS

*Biomimetics* is an international interdisciplinary forum for the publication of original papers in areas at the intersection of biology and engineering. The journal publishes research papers and short notes (2000 words or less) on: mechanical and chemical analysis of structural biological materials leading to an understanding of their performance; development and production of materials based on direct copying of nature; analysis of the mechanical performance of materials produced using biotechnological processes; novel applications of biomimetic materials; improvements in the design of current organisms based on mechanical analysis of their structure; and analysis of the optimization criteria used in natural materials and structures. *Biomimetics* also publishes letters to the editor (published at the editor's discretion), book reviews, and announcements of relevant meetings.

## CO-EDITORS

J. F. V. Vincent

A. V. Srinivasan

Centre for Biomimetics

Department of Mechanical Engineering

University of Reading

University of Connecticut

Reading, England

Storrs, Connecticut, USA

(General Biology)

(Mechanics of Materials, Aeroelasticity)

## EDITORIAL BOARD

F. G. Barth, Institut für Zoologie, Vienna, Austria (Sensory Systems)

J. Campbell, Naval Research Laboratory, Washington, D.C., USA (Biotechnology)

G. Jeronimidis, University of Reading, Reading, England (Composites)

D. Kaplan, Department of the Army RD&E Center, Natick, Massachusetts, USA (Biochemistry)

W. M. Lee, The Dow Chemical Col., Midland, Michigan, USA (Polymer Science)

Y.-W. Mai, The University of Sydney, Sydney, New South Wales, Australia (Engineering)

A. Michelsen, Biologisk Institut, Odense, Denmark (Behavior)

II. Okamoto, Sumitomo Chemical Co. Ltd., Osaka, Japan (Engineering Design)

K. Simkiss, University of Reading, Reading, England (Bioceramics)

J. II. Waite, University of Delaware, Lewes, Delaware, USA (Adhesion)

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# Biomimetics

Volume 2, Number 2

June 1994

## CONTENTS

Special Issue: Plant Biomechanics Congress

Montpellier, France, September 5-9, 1994

<table><tr><td>Biomechanics in Botany: A General Introduction<br><i>Julian F. V. Vincent</i></td><td>77</td></tr><tr><td>On the Research History of Plant Biomechanics<br><i>Werner Nachtigall</i></td><td>87</td></tr><tr><td>Bending Stability of Plant Stems: Ontogenetical, Ecological, and Phylogenetical Aspects<br><i>Thomas Speck</i></td><td>109</td></tr><tr><td>The Biomechanics of Root Anchorage<br><i>A. R. Ennos</i></td><td>129</td></tr><tr><td>Wind Damage to Forests<br><i>B. A. Gardiner and C. P. Quine</i></td><td>139</td></tr><tr><td>Local Buckling and Other Modes of Failure in Hollow Plant Stems<br><i>H.-Ch. Spatz and T. Speck</i></td><td>149</td></tr><tr><td>Growth and Architecture of the Plant Cell Wall: Biomechanical Problems<br><i>Roger Prat, Michèle Mosiniak, and Jean-Claude Roland</i></td><td>175</td></tr></table>
# Biomechanics in Botany: A General Introduction<fnref n="1" />

Julian F. V. Vincent<fnref n="2" />

Plants are ideal subjects for biomechanics, often better than animals. At our current levels of understanding there are several problems which seem ready to be solved. These are the energetics of cell shape, wound repair and growth, the structural parameters of turgor systems, the energetics of lignification, plant form and evolution, plants as foods, designing for fracture, plants as a renewable resource for structural materials, and biomimicry of the structures and mechanisms of plants. A checklist is provided, covering these and related topics.

**KEY WORDS:** plants; growth; cellular mechanics; turgor; cell shape; lignification.

## INTRODUCTION

Plants are a far more convenient subject for the study of biological engineering than are animals. They are more simply constructed, have fewer cell types, do not move around nearly so much, are easier to maintain under experimental conditions, and do not require a license for their experimentation. At the same time we can learn general principles from them such as mechanical sensing and response at the cellular level, the pros and cons of hierarchical construction, and the nature of mechanical optimization in biology.

The mechanisms used to reach the shapes of plants (morphogenesis) and the mechanical properties and possibilities of those shapes (biomechanics) form the bulk of the subject matter of this conference. In addition, the mechanical properties and design of plants are important in food science, agriculture, horticulture, etc., and can suggest ideas for technology (Velcro is a well-known example). I highlight some problems in plant biomechanics which I see as

<footnote n="1">¹This is the published version of a paper presented at the Plant Biomechanics Congress, Montpellier, France, September 5-9, 1994.</footnote>

<footnote n="2">²Centre for Biomimetics, The University, Reading RG6 2AT, United Kingdom.</footnote>
interesting. One of the purposes of a conference like this must be for people to assess each other's lists of imperatives and modify them accordingly. A collection of attributes and ideas which can be used as a checklist and framework for the conference appears in Fig. 1.

CELLS

D'Arcy Thompson (1917) showed that the shapes of many cells could be mimicked by soap films. In some ways this was a disservice, since some think that the shape of cells is defined by the same balance of forces which shapes soap bubbles. That the shapes are similar is true not only of isolated cells but of cells surrounded by others (Marvin, 1939). However, it is also true that the soap film, being fluid, cannot support shear. Therefore the curves which a soap film, and many plant cell walls, displays are those in which there is no shear. This will necessarily be energetically cheaper to construct and therefore the shape of choice. It should therefore be possible to make some predictions: In an environment where energy is scarce, the shapes of cells will be simple. As the availability of energy increases, cells will take on more complex shapes, which will help them access energy more effectively but which themselves will require more energy for maintenance. The optimization is obvious; the experiments require some estimate to be made of the energy requirements of assuming shapes which are varying distances from a shear-free shape and the increased efficiency of those shapes.

The subcellular morphology of plants is well documented, but the mechanical significance is still under debate. Of the cellular components, microtubules are probably the stiffest materials and so are the most obvious candidates for the maintenance of shape. Anisotropy in their arrangement can lead to specific shapes, and changes in their arrangement can lead to changes in shape. This has been observed as part of the process of wound healing (Hush *et al.*, 1990; Hush and Overall, 1991). But how does the cell sense wounding of the tissue within which it sits? The biochemist would immediately talk of chemicals released from cells; the engineer would think about detection of nonuniform strain fields. Events at the apical meristem such as determination of leaf primordia have been associated with nonuniform strain distribution in the cell walls, due either to natural causes or to specific lesions caused by laser. The implication must be that the biochemistry, if it does not lead (which I think is unlikely), must follow the distribution of strain (Steucek *et al.*, 1992) modulated by turgor pressure and the anisotropic orientation of cellulose fibrils in the cell wall (Green, 1991). The strain is probably sensed by changes in membrane permeability—a specific pathway opens up in the cell membrane. Certainly animal cells can respond to changes in shape by changing their synthetic pathways (B. Thorp, personal communication) and do so in a remarkably short time. In Reading we
Subcellular morphology

Cellular components

**CELLULAR MECHANISMS**
*   microtubules
*   microfibres / filaments
*   membrane properties
*   cell walls
*   turgor

**Form / habit**
*   floating
*   climbing

**ECOLOGY**
*   creeping
*   free-standing

**Biotic interactions**
*   plants
*   animals
*   defences - leaves, stems, seeds

**EVOLUTION**
*   Complexity cell types
*   Emergence on to land

*   Load transfer

*   Scale effects

*   Stem cylinder / beam

*   Flowers (tissue tensions?)

**MORPHOLOGY**
*   Leaves

*   Fruit

*   Seeds epidermis / skin

*   Tissues parenchyma

*   fibres

*   hierarchies

**PHYSIOLOGY**
*   Growth
*   Wound response
*   Differentiation

**AGRICULTURE**
*   Crops lodging, cracking
*   Harvesting
*   Fractionation
*   Processing

**BEHAVIOUR**
*   Tropisms
*   Abscission / dehiscence
*   Taxis
*   Sensory

**MATERIALS**
*   Wood, bark
*   Fibre rope, composites
*   Leaves
*   Seeds nuts, vegetable ivory

**FOOD**
*   Breeding Processing
*   Texture Transport

*   Wood analogues

*   Cellular materials

**BIOMIMICRY**
*   open / closed
*   turgor - static / dynamic
*   Hierarchy / optimisation

Fig. 1. A collection of attributes and ideas that can be used as a checklist and framework for the conference.