Proceedings of the 1st Plant biomechanics International
conference

Bernard Thibaut, Joseph Gril, Bernard Chanson, Caroline Loup, Jeronimidis Georges

► To cite this version:

Bernard Thibaut, Joseph Gril, Bernard Chanson, Caroline Loup, Jeronimidis Georges. Proceedings of the 1st Plant biomechanics International conference. Plant Biomécanics, Sep 1994, Montpellier, France. 390 p., 2021, Colloque Interdisciplinaire du Comité National de la recherche scientifique. hal-03250935

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# BIOMÉCANIQUE DES VÉGÉTAUX
## PLANT BIOMECHANICS
### MONTPELLIER 5-9 SEPTEMBRE 94

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W. Albrecht, J.P. Boeke, R.R. Archer, P. Bruns, J. de Brabec, M. Braker, H. Bräckler, P.W. Barlow, K.M. Brat, J.P. Bouillet, A. Brundage, G. K. M. Burrows, B.CBRABBLE, B.CBRABBERT, B. CBRAHMAN, H. CHEN, M.F. CHENG, I. CHOUQUET, J.G. CONDERAS, R. A. CONDERAS, P. CRABBE, M.J. CAO, D. COOK, P. CAUZIAT, G.R. DAYVILAKI, D. DELACAY, J.F. DEME, A.J. DOW, K. DEW, D. DEWELL, J.L. DEAND, C. DEBELIN, B. DEBRADAMAN, R. DEBOS, A.G. DEFRASNE, T.J. DOSTER, M. D'FOURCROU, M. T. D'FOURCHIER, H.R. FRANÇOIS, J. GALTIER, B. GRANDIER, L.J. GIBBON, P. GLEIBER, B. GRIGORIE, J. GRIL, V. GRIGOSO, P. GRINNAN, H. GRUBET, W. GRUEN, D. GRUTTORD, R. HABERMANN, F. HALL, E. HARTZLER, Z. HERBOWEZ, D. G. HELLER, M.S. HAYNES, M. HART, F. G. HERNIMAN, J.L. HOLLIDAY, D. JULIEN, J.L. KERGUNE, R.B. KESSEL, R.B. KRAB, B. KESLING, R. LAURASSIN

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B. LUSON

J.D. LAVIN, J.G. LaTIMIER, J. LICHT, P. LILLFORD, P.M. LINN, J.H. Liu, P. LILHAC, J.H. Liu, P. LOBIN, C. LOMP, P. LUCAS, C. MATTHEW, J.C. MARGET, M. McCann, T. McCABRY, B. MILLET, B. MIGLIOTTI, V. MOSSERIN, W. MOSSER, B. MOULIER, W. NACHMANSALL, T. NAKAMURA, M. NILSSON, H. OKAMOTO, T. OKUYAMA, J.K.E. OATSBURG, M. PARMATTHAM, G. PERBAL, R. PRAT, J. PITCHARD, N. PUTZ, C. ROGE, J.C. ROLAND, A. ROW, R.C. ROURCET, N. ROWE, K. RUDEL, F. RASSUS, F. SCHWIER, J. SELL, D. SHAR, R. SIEBEN, D. SHAR, W. K. SILK, N. SOUTY, H.C. STOKES, T. SPECK, R. STOTT, B. M. STUKES, C. SURENDURAN, M. TATEO, F. TELEWICZ, C. SURENDRAN, M. TESCHNER, B. TRIBAUD, R. TRIGMA, S.H.P. TALKIEN, M.B. TRIBOUOT, X. VANSEWALLE, J. VENGE, J. VOCKE, H. VAREUX, U.G. WEEST, L. WESSOLLY, E. WITTE, J. ZEBROWSKI, E. ZORCHER, ET...

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CENTRE NATIONAL
DE LA RECHERCHE
SCIENTIFIQUE

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Institut National de la Recherche Agronomique

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Centre
de coopération
internationale
en recherche
agronomique
pour le
développement

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Université Montpellier I.
Sciences et Techniques du Languevin

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AGROPOLIS

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REGION LANGUEDOC ROUSSILLON

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<figure><img src="image_12.png" /><figcaption>Conference poster by Bernard CHANSON - 1994
(the name of participants is indicated on both sides)</figcaption></figure>
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CENTRE NATIONAL
DE LA RECHERCHE
SCIENTIFIQUE

<figure><img src="image_14.png" /></figure>

INRA
Institut National de la Recherche Agronomique

<figure><img src="image_15.png" /></figure>

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Université Montpellier II,
Sciences et Techniques du Languedoc

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ELSEVIER

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Actes - Proceedings

5-9 septembre 1994

Colloque interdisciplinaire
du Comité national
de la recherche scientifique

Montpellier - France
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AGROPOLIS

<figure><img src="image_20.png" /></figure>

REGION
Languedoc
Roussillon

LIR
MULTIPOLE
TECHNOLOGIQUE
REGIONAL
LANGUEDOC-ROUSSILLON

Le colloque de biomécanique des végétaux est
organisé sous l'égide du Centre national de la
recherche scientifique (CNRS).

Avec la participation de :

✓ Institut national de la recherche agronomique (INRA)

✓ Université de Montpellier II (UM II)

✓ Centre de coopération internationale de recherche agronomique pour le développement (CIRAD).

Et le soutien de :

✓ Agropolis

✓ Conseil régional du Languedoc-Roussillon

✓ Multipôle technologique régional du Languedoc-Roussillon.
# Biomécanique des végétaux
*Plant biomechanics*

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## RÉSUMÉS - SUMMARIES

Colloque interdisciplinaire
du Comité national de la recherche scientifique
Montpellier (France) du 5 au 9 Septembre 1994
# PRÉFACE

Ce colloque est le résultat d'une volonté affichée par le Comité national de la recherche scientifique : promouvoir l'interdisciplinarité, c'est-à-dire la rencontre et la mise en commun des compétences de disciplines différentes pour aborder des grands problèmes de la recherche actuelle.

La biomécanique des végétaux est typiquement un champ de recherches qui nécessite la synergie entre des scientifiques de la biologie végétale, de la modélisation des systèmes complexes et de la mécanique des matériaux et des structures.

Elle a pour objectif :

* une meilleure compréhension de la morphogenèse et du fonctionnement des organes de soutien chez les plantes,

* une contribution à l'analyse des relations entre fonctionnement des plantes cultivées et qualité de la production,

* une analyse de la croissance, du développement, de la structure et particulièrement de la tenue mécanique des plantes modifiées par l'homme ou son environnement,

* le développement, grâce à l'étude des végétaux, de procédés et de types de constructions originaux, inspirés des phénomènes biologiques (bionique ou biomimétique).

Depuis quelques années cette thématique nouvelle a connu un développement important en Amérique du Nord, au Japon et en Europe, notamment en Grande-Bretagne, en Allemagne et en France.

L'intiative du Comité national a donc permis d'organiser le premier colloque international entièrement dédié à la biomécanique des végétaux et l'ensemble des résumés de communications volontaires<fnref n="1" /> ci-après reflète bien les principaux axes de recherches développés actuellement. A côté des préoccupations fondamentales sur la morphogenèse et la croissance des végétaux, se retrouvent des recherches plus finalisées visant à répondre aux demandes des forestiers, du monde agricole, des industries agroalimentaires ou des gestionnaires de parcs et jardins. Ces aller-retours entre la connaissance et les applications constituent le deuxième point fort de ce colloque qui se veut d'abord un moment de rencontre entre les uns et les autres.

Bernard THIBAUT
Président du Comité d'organisation

<footnote n="1">¹ L'ensemble des textes des communications invitées fait l'objet d'une publication séparée dans 2 numéros spéciaux de la revue *Biomimetics*.</footnote>
FOREWORD

This congress is the result of a voluntary policy of the French National Committee for Scientific Research to promote interdisciplinarity. Some of the major problems encountered by present research require the collaboration and association of abilities from various disciplines.

Plant biomechanics is a typical case, since it requires a synergy between scientists involved in plant biology, the modelling of complex systems, and the mechanics of materials and structures.

This field aims at improving the understanding and analysis of:

* morphogenesis and function of supporting organs in plants;

* relationships between mechanical functions of cultivated plants and the quality of crops;

* growth, development, structure and mechanical strength of plant systems relative to modifications imposed by man and the environment;

* plant mechanical, structural and responsive designs as paradigms, in a biomimetic sense, for man-made applications.

During the last few years, this new theme has been developed in North America, Japan and Europe, particularly in Great Britain, Germany and France.

The first international congress entirely devoted to plant biomechanics is thus due to the initiative of the national committee. The following collection of voluntary contributions<fnref n="2" /> reflects the main axes of the research under development, either basic approaches to morphogenesis and plant growth, or applied research aiming to meet the needs of foresters, the agricultural sector, the food industry and park managers. The level of interaction between specialists in basic and applied knowledge is another strong feature of this congress, which should be, primarily, an occasion to meet others.

Bernard THIBAUT
President of the Organising Committee

<footnote n="2">² The text of invited papers has been published separately in two special issues of *Biomimetics*.</footnote>
COMITÉ SCIENTIFIQUE - SCIENTIFIC COMMITTEE

<table><tr><td>R.R. ARCHER</td><td>Univ. of Massachusetts (USA)</td></tr><tr><td>P. BAAS</td><td>Hortus Botanicus (N)</td></tr><tr><td>J. CRABBE</td><td>Univ. Gembloux (B)</td></tr><tr><td>P. CRUIZIAT</td><td>INRA Clermont-Ferrand (F)</td></tr><tr><td>A.R. ENNOS</td><td>Univ. Manchester (UK)</td></tr><tr><td>B. GARDINER</td><td>Forestry Commission (UK)</td></tr><tr><td>D. GUITARD</td><td>Univ. Bordeaux (F)</td></tr><tr><td>F. HALLE</td><td>Univ. Montpellier (F)</td></tr><tr><td>M. JAFFE</td><td>Wake Forest Univ. (USA)</td></tr><tr><td>G. JERONIMIDIS</td><td>Univ. Reading (UK)</td></tr><tr><td>B. MONTIES</td><td>INRA Grignon (F)</td></tr><tr><td>V. MOSBRUGGER</td><td>Univ. Tübingen (D)</td></tr><tr><td>J.C. ROLAND</td><td>Univ. Paris VI (F)</td></tr><tr><td>K. RUEL</td><td>CNRS Grenoble (F)</td></tr><tr><td>W. SILK</td><td>Univ. Davis (USA)</td></tr><tr><td>T. SPECK</td><td>Univ. Freiburg (D)</td></tr><tr><td>H.-Ch. SPATZ</td><td>Univ. Freiburg (D)</td></tr><tr><td>B. THIBAUT</td><td>CNRS Montpellier (F)</td></tr><tr><td>J. VINCENT</td><td>Univ. Reading (UK)</td></tr></table>

COMITÉ D'ORGANISATION - ORGANISING COMMITTEE

<table><tr><td>B. CHANSON</td><td>CNRS Bordeaux (F)</td></tr><tr><td>J.L. DURAND</td><td>INRA Lusignan (F)</td></tr><tr><td>M. FOURNIER</td><td>ENGREF Paris (F)</td></tr><tr><td>J. GRIL</td><td>CNRS Montpellier (F)</td></tr><tr><td>G. JERONIMIDIS</td><td>Univ. Reading (UK)</td></tr><tr><td>C. LOUP</td><td>Univ. Montpellier II (F)</td></tr><tr><td>B. MOULIA</td><td>INRA Grignon (F)</td></tr><tr><td>T. SPECK</td><td>Botanical Garden Freiburg (D)</td></tr><tr><td>B. THIBAUT</td><td>CNRS Montpellier (F)</td></tr></table>

Pour des renseignements complémentaires contacter - For additional information please contact

Bernard THIBAUT

LMGC "Bois", CP 081

Université Montpellier II - Place E.-Bataillon

34095 MONTPELLIER CEDEX 5 - FRANCE

Tel : (33) 67 14 34 31 - Fax : (33) 67 54 48 52

E-mail : jgril@lmgc.univ-montp2.fr
## SOMMAIRE

<table>
  <tbody>
    <tr>
      <td>Albrecht, W., Bethge, K. & Mattheck, C. Optimized distribution of lateral strength in trees</td>
      <td>13</td>
    </tr>
    <tr>
      <td>André, J.-P. Etude par micromoulage de l'architecture vasculaire de la plante entière</td>
      <td>15</td>
    </tr>
    <tr>
      <td>Archer, R.R. Induction of reaction wood : the loop experiment revisited</td>
      <td>17</td>
    </tr>
    <tr>
      <td>Baillères, H., Chanson, B., Fournier, M., Tollier, M.-T. & Monties, B. Wood structure, chemical composition and growth strains in Eucalyptus clones. Interpretation of the noticed phenomenons</td>
      <td>21</td>
    </tr>
    <tr>
      <td>Baillères, H., Chanson, B. & Fournier, M. Two field measurement techniques for appraising the longitudinal growth strains at the stem surface</td>
      <td>23</td>
    </tr>
    <tr>
      <td>Baker, C.J., Griffin, J.M., Scott, R.K. & Sylvester-Bradley, R. Lodging : the development of a risk assessment technique based on a mechanical model</td>
      <td>25</td>
    </tr>
    <tr>
      <td>Barlow, P.W., Lück, J. & Lück, H.B. Patterns and programs of cell division in root meristems of maize and tomato</td>
      <td>27</td>
    </tr>
    <tr>
      <td>Bhat, K.M. Structural basis for the biomechanical behaviour of rattan material</td>
      <td>29</td>
    </tr>
    <tr>
      <td>Bouillet, J.-P. Régulation de la forme du tronc de Pinus kesiya dans la région du Mangoro (Madagascar) : indépendance entre la forme de la section droite et la compétition inter-individus</td>
      <td>31</td>
    </tr>
    <tr>
      <td>Burrows, K.M. Finite element analysis of the mechanical properties of plant cells</td>
      <td>33</td>
    </tr>
    <tr>
      <td>Caballé, G. & Hallé, F. Autoportance vs non autoportance : ses expressions anatomiques et morphologiques chez les lianes</td>
      <td>35</td>
    </tr>
    <tr>
      <td>Chabbert, B., Monties, B., Zieslin, N. & Ben-Zaken, R. Changes in lignification in rose flower peduncles differing by their resistance to bending</td>
      <td>37</td>
    </tr>
    <tr>
      <td>Chen, H., Duprat, F., Grotte, M., Loonis, D. & Pietri, E. Influence of the inhomogeneity of the apple on the response spectra during nondestructive acoustic sensing of fruit firmness</td>
      <td>39</td>
    </tr>
    <tr>
      <td>Choong, M.F. Predictability of leaf toughness from anatomical studies</td>
      <td>41</td>
    </tr>
  </tbody>
</table>
<table>
  <tbody>
    <tr>
      <td>Grzeskowiak, V. & Sassus, F. Coloration macroscopique du bois de tension chez le peuplier</td>
      <td>73</td>
    </tr>
    <tr>
      <td>Habermehl, A. & Ridder, A.-W. Computerized tomography - A non destructive method for evaluating the mechanical properties and strength of trees</td>
      <td>75</td>
    </tr>
    <tr>
      <td>Hatsch, E., Rittie, D. & Dhôte, J.-F. Défilement du tronc chez le chêne sessile ; test de différents modèles et influence de l'architecture</td>
      <td>77</td>
    </tr>
    <tr>
      <td>Hejnowicz, Z. & Sievers, A. Tissue stresses, their origin and biomechanical significance</td>
      <td>79</td>
    </tr>
    <tr>
      <td>Hepworth, D.G. The mechanical properties of transgenic plants with modified lignin.</td>
      <td>81</td>
    </tr>
    <tr>
      <td>Hiller, S. Turgor / mechanical property relations in potato tuber parenchyma</td>
      <td>83</td>
    </tr>
    <tr>
      <td>Irving, M.S., Ritter, S., Koller, D. & Tomos, A.D. The mechanism of leaf movement in bean Phaseolus vulgaris</td>
      <td>85</td>
    </tr>
    <tr>
      <td>Jeronimidis, G. & Liu, J.H. Analysis of the mechanical response of cellular turgid plant tissue</td>
      <td>87</td>
    </tr>
    <tr>
      <td>Jeronimidis, G. & Stühlen, B.M. Mechanical response of plant tissue to imposed compressive deformations</td>
      <td>89</td>
    </tr>
    <tr>
      <td>Jeronimidis, G. & Tolkien, S.H.P. Imaging of cellular deformations for plant biomechanics</td>
      <td>91</td>
    </tr>
    <tr>
      <td>Julien, J.-L., Boyer, N., Desbiez, M.-O. & Maugé, J.-C. Growth responses to mechanical stimulation in some herbaceous plants</td>
      <td>93</td>
    </tr>
    <tr>
      <td>Jullien, D. Evaluating transverse strains in green wood</td>
      <td>95</td>
    </tr>
    <tr>
      <td>Karam, G.N. & Gibson, L.J. Biomimicking of plant stems</td>
      <td>97</td>
    </tr>
    <tr>
      <td>Kesel, A.B., Nachtigall, W. & Wisser, A. Bending pattern of grasses with differing construction</td>
      <td>99</td>
    </tr>
    <tr>
      <td>Khan, A.A. Fracture properties of an anisotropic biological cellular material - Apple flesh</td>
      <td>101</td>
    </tr>
    <tr>
      <td>Kresling, B. Plant "design" : mechanical simulations of growth patterns and bionics</td>
      <td>103</td>
    </tr>
    <tr>
      <td>Lahbabi, R., Perré, P. & Brandão, A. Measurement of deformation using image analysis</td>
      <td>105</td>
    </tr>
    <tr>
      <td>Latimer, J.G. Summary of vegetable transplant response to mechanical conditioning via brushing</td>
      <td>107</td>
    </tr>
    <tr>
      <td>Lesage, P. & Destain, M.-F. Mise au point d'un dispositif de mesure non destructif de la fermeté des fruits et des légumes. Essais sur la tomate</td>
      <td>109</td>
    </tr>
  </tbody>
</table>
<table>
  <tbody>
    <tr>
      <td>Lichou, J., Audubert, A., Edin, M. & Broquaire, J.-M. Appareil de mesure de la résistance au cassage de scions d'arbres</td>
      <td>111</td>
    </tr>
    <tr>
      <td>Lintilhac, P.M. The sporangium as a biomechanical device</td>
      <td>113</td>
    </tr>
    <tr>
      <td>Lintilhac, P.M., Galanes, S. & Outwater, J. Continuous bending moment measurements from gravitropically responding roots</td>
      <td>115</td>
    </tr>
    <tr>
      <td>McCann, M.C. & Roberts, K. Changes in wall architecture during plant cell growth and differentiation</td>
      <td>117</td>
    </tr>
    <tr>
      <td>McGarry, A. Cellular basis of tissue strength in carrots</td>
      <td>119</td>
    </tr>
    <tr>
      <td>Millet, B., Bonnet, B. & Badot, P.M. Problèmes mécaniques inhérents au mouvement révolutif d'exploration des tiges volubiles</td>
      <td>121</td>
    </tr>
    <tr>
      <td>Mosbrugger, V. Biomechanics and evolution of plant form</td>
      <td>123</td>
    </tr>
    <tr>
      <td>Nakamura, T., Saotome, M., Yamazaki, T., Baba, K., Itoh, T. & Yokoyama, T. The effect of gibberellin on weeping of growing branches of the Japanese cherry, Prunus spachiana</td>
      <td>125</td>
    </tr>
    <tr>
      <td>Nilsson, M. Internal stresses due to growth and differentiation in Norway spruce - measurements and results</td>
      <td>127</td>
    </tr>
    <tr>
      <td>Okamoto, H. & Okamoto, A. Biomechanical control of elongation growth by phytohormones and osmotic stress</td>
      <td>129</td>
    </tr>
    <tr>
      <td>Okamoto, A., Katou, K. & Okamoto, H. How to determine the biomechanical growth parameters in vivo and in vitro ? A theoretical and technical note</td>
      <td>131</td>
    </tr>
    <tr>
      <td>Okuyama, T., Yoshida, M., Yamamoto, H. & Sakai, T. A physical behavior of tree during secondary growth</td>
      <td>133</td>
    </tr>
    <tr>
      <td>Ortega, J.K.E. Plant and fungal cell growth: governing equations for cell wall extension and water transport</td>
      <td>135</td>
    </tr>
    <tr>
      <td>Paramathma, M. & Surendran, C. Estimation of gene action governing the morphological attributes in Eucalyptus species</td>
      <td>137</td>
    </tr>
    <tr>
      <td>Perbal, G. & Driss-Ecole, D. Effects of gravity and microgravity on root growth and statocyte polarity</td>
      <td>139</td>
    </tr>
    <tr>
      <td>Perré, P. & Shang D.K. Wood moisture content measurement by X-ray exposure method</td>
      <td>141</td>
    </tr>
    <tr>
      <td>Philippi, U., Kesel, A.B. & Nachtigall, W. Biomechanics of grasses - Functional-morphological studies using finite element method</td>
      <td>143</td>
    </tr>
    <tr>
      <td>Pritchard, J. & Tomos, D. The biophysics of root growth</td>
      <td>145</td>
    </tr>
    <tr>
      <td>Pütz, N. & Hüning, G. Undergrownd plant movement by contractil roots. An experimental approach to the functionality of channel formation</td>
      <td>147</td>
    </tr>
    <tr>
      <td>Roth, A. Water transport in vessel elements with helical thickenings</td>
      <td>149</td>
    </tr>
  </tbody>
</table>
<table>
  <tbody>
    <tr>
      <td>Roudot, A.-C., Studman, C.J. &amp; Duprat, F. Morphogenèse et fermeté de la pomme</td>
      <td>151</td>
    </tr>
    <tr>
      <td>Rowe, N.P. &amp; Speck, T. Fossil plants: biomechanics as an aid to interpreting growth form and habit</td>
      <td>153</td>
    </tr>
    <tr>
      <td>Ruel, K. &amp; Joseleau, J.-P. An ultrastructural study of the qualitative distribution of lignin in a developing internode of maize</td>
      <td>155</td>
    </tr>
    <tr>
      <td>Sandoz, J.-L. &amp; Lorin, P. Standing tree quality assessments using ultrasound</td>
      <td>157</td>
    </tr>
    <tr>
      <td>Sassus, F., Thomas, R., Grzeskowiak, V., Chanson, B., Fournier, M. &amp; Thibaut, B. Contraintes de croissance et morphologie chez un clone de peuplier (I214)</td>
      <td>159</td>
    </tr>
    <tr>
      <td>Schwarze, F.W.M.R., Lonsdale, D., Mattheck, C. &amp; Fink, S. 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</td>
      <td>161</td>
    </tr>
    <tr>
      <td>Sell, J. Mechanical aspects of new SEM observations on the fibril / matrix structure of the S2 layer of softwood tracheids</td>
      <td>163</td>
    </tr>
    <tr>
      <td>Sierra de Grado, R. &amp; Ricardo, A.M. Differences in phototropic sensitivity, stem straightness and compression wood formation in Pinus pinaster Ait., Pinus canariensis Sweet. and Pinus nigra Arn. seedlings</td>
      <td>165</td>
    </tr>
    <tr>
      <td>Silk, W.K. Kinematics of twining growth and mechanics of the twining habit</td>
      <td>167</td>
    </tr>
    <tr>
      <td>Souty, N. &amp; Rode, C. A mechanistic study of seedlings emergence from under superficial obstacles</td>
      <td>169</td>
    </tr>
    <tr>
      <td>Spatz, H.C. Mechanical stability of Hollow trees</td>
      <td>171</td>
    </tr>
    <tr>
      <td>Stokes, A. &amp; Mattheck, C. Effect of branching on the internal distribution of strength within a root system</td>
      <td>173</td>
    </tr>
    <tr>
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      <td>175</td>
    </tr>
    <tr>
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      <td>177</td>
    </tr>
    <tr>
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      <td>179</td>
    </tr>
    <tr>
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    <tr>
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    <tr>
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    </tr>
  </tbody>
</table>
<table>
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    <tr>
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    </tr>
    <tr>
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    </tr>
    <tr>
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    </tr>
  </tbody>
</table>
## Optimized distribution of lateral strength in trees.

Albrecht, W., Bethge, K., Mattheck, C.

Kernforschungszentrum Karlsruhe
Institut für Materialforschung II
Postfach 3640
76021 Karlsruhe
Germany

## Summary

Through evolution and competition with other living forms, trees had to optimize themselves. Metzger [1] was the first who found a relationship between tree design and mechanical loading. He showed that the stem of spruce trees taper in a manner which leads to a constant mechanical stress along the surface. This principle of even load distribution was generalized to biological load carriers and was called "Constant Stress Axiom" by Mattheck and co-workers. [2,3,4] The constant stress axiom is limited to the surface of the tree. Nevertheless, even intact trees could fail by the failure mode described in Fig. 1. This failure mode is caused by internal lateral stress.

<figure><img src="image_22.png" /><figcaption>Fig. 1: Failure of root stem joint</figcaption></figure>

If a curved beam is bent in order to be straightened, lateral tensile stresses in the radial direction could not be avoided [5]. These tensile stresses are zero on the surface and have their maximum inside the structure. In trees a lot of curved beams are hidden and are called hazard beams. Every curved stem, every curved branche or root stem joint could act as a hazard beam. If they were straightened they often fail by delamination of the wood fibres. In order to find out whether there is some reaction in the tree to avoid this failure mode, more than 15 different trees have been studied. A side-view photograph was taken from each of them and a 2-dimensional finite element calculation was done under bending load, in order to get the stress distribution perpendicular to the grain inside the tree. A sample of drilling cores where taken out of the tree with a 5mm diameter increment borer. At the Karlsruhe Nuclear Research Center a small wood testing device called Fractometer [6] (see Fig. 2) was developed to measure the bending strength of increment cores. The cylindrical samples had been broken successively along their length with the Fractometer. Strength distribution within the core and from core to core within the stem was recorded. In any case there was an evident increase in lateral strength in the same zone where highest lateral stresses perpendicular to the grain were computed in the previously calculated FE-model (see Fig. 3).

In simple words: the measured splitting resistance is highest where the greatest splitting stresses are computed.
So there is further evidence to suggest that strength of wood is controlled by local
mechanical stress.

<figure><img src="image_23.png" /><figcaption>Fig 2: Fractometer</figcaption></figure>

Wood rays run into the direction in which lateral splitting stress is acting. So it is
very easy to imagine that the wood ray system is mainly responsible for lateral
strength. Also there must be an adaptive mechanism which enables the tree to
detect laterally highly loaded zones and prevent tree splitting by increasing the
wood quality, i.e. the lateral strength which is the resistance against splitting.

<figure><img src="image_24.png" /><figcaption>Fig. 3: Stress and strength distribution perpendicular to the grain</figcaption></figure>

References

[1] Metzger, K. Der Wind als maßgeblicher Faktor für das Wachstum der Bäume, Mündener forstliche Hefte, Springer Verlag, Berlin 1893

[2] Mattheck, C. Trees- the mechanical design, Springer Verlag, Heidelberg 1991

[3] Mattheck, C. Design in der Natur, Rombach Verlag, Freiburg 1992

[4] Mattheck, C., Breloer, H., Handbuch der Schadenskunde von Bäumen - der Baumbruch in Mechanik und Rechtsprechung, Rombach Verlag, Freiburg 1993

[5] Young, W., Roark's Formulas for Stress & Strain, McGraw-Hill Book Company, New York, 6th edition

[6] Mattheck, C., Bethge, K., Das Fractometer: Ein Prüfgerät für Holz im Taschenformat, Allg. Forst Zeitschrift, Nr.3, 1993
# ETUDE PAR MICROMOULAGE DE L'ARCHITECTURE VASCULAIRE DE LA PLANTE ENTIERE

J.P. ANDRÉ - INRA - ANTIBES

On entend ici par architecture vasculaire de la plante entière la disposition des vaisseaux d'origine procambiale (xylème primaire), puis d'origine cambiale (xylème secondaire), dans les faisceaux qui relient les axes de la plante à leurs organes adjacents. Elle est en grande partie déterminée par la phyllotaxie de l'espèce.

L'examen des connexions vasculaires dans les zones nodales et le suivi des trajets longitudinaux des vaisseaux de grande longueur présentent des difficultés d'ordre histologique bien connues.

Une technique récente consistant à matérialiser la lumière des vaisseaux par remplissage avec un polymère réticulable, puis à dégager ces moulages internes par destruction totale ou partielle des parois du xylème, fournit une vision nouvelle de ce tissu et un utile complément aux techniques histologiques classiques.

Plus généralement, la technique permet le moulage de la lumière de toute cellule du xylème (fibre, trachéide, parenchyme) et d'autres tissus, à la condition qu'elle soit vide et que sa paroi primaire soit, en un point, poreuse au polymère.

L'excellente définition de surface du moulage paraît être de l'ordre de 0,1 µm.

L'architecture vasculaire du plant de tomate est choisie ici pour illustrer les possibilités nouvelles d'investigation de la technique des micromoulages.

## BIBLIOGRAPHIE :

ANDRÉ, J.P., 1993 - Micromoulage des espaces vides intra et intercellulaires dans les tissus végétaux. C.R. Ac. Sc. Paris, 316, 1336-41.

FUJII, T., 1993 - Application of a resin casting method to wood anatomy of some japanese Fagacae species. IAWA J. 14 (3) 273-288.
ARCHITECTURE VASCULAIRE DU PLANT DE TOMATE

<figure><img src="image_25.png" /></figure>

<figure><img src="image_26.png" /></figure>

<figure><img src="image_27.png" /></figure>

<figure><img src="image_28.png" /></figure>

<figure><img src="image_29.png" /></figure>

<figure><img src="image_30.png" /></figure>
# Induction of reaction wood : the loop experiment revisited

R.R. ARCHER

University of Massachusetts

Amherst, Mass. U.S.A.

## Introduction

For a more complete discussion of the induction of reaction wood, see the review article Wilson & Archer 1977. The literature contains a large number of experiments where branches or stems are tilted or bent into various configurations. Most of these experiments are designed to prove or disprove various hypotheses with the goal of showing that a single stimulus is involved.

Many of these experiments involved bending stems into partial and full loops. In some cases, conclusions as to the role of compressive or tensile stresses in the induction of reaction wood were made. For example, Sinnott (1952) reports the observation by Ewart & Mason-Jones (1906) that for the vertical loop experiment, compression wood "did not develop on the inside of the entire loop, as it should have done if compression were the factor chiefly involved, but formed on the lower side of both the upper and lower portions of the loop, as if gravity determined its position". In the course of bending the stem into a loop, the initial stress state is indeed compressive on the inside of the entire loop. Cells in the cambial zone on the inside of the loop are developing adjacent to mature cells that have been compresses. Cells either attempt to expand in place or to contract depending upon whether they are compression or normal wood cells. These growth strains can produce considerable stresses and deformation of the loop. Depending upon how the loop is supported, a new increment of stress is produced in the new layer of cells (Archer, 1987). This new stress state can be very different from the initial stress state, and as this process is reprated in layer after layer, one can test the stress hypothesis that cells that develop in cambial zones adjacent to xylem in a state of compression become compression wood. In the present paper, our objective is to present the analysis which would seem to be necessary in order to apply the stress hypothesis to a given problem where mechanical action of reaction wood is involved.

## Analysis

The stem is modeled as a tapered elastic rod which is subjected to a set of loads to deform it into some desired state and then it is supported so as to remain fixed at one or more points. For a given time interval, a small increment of radial growth takes place. Where radially adjacent xylem cells in a state of compression/tension then compression/tension wood cells develop elsewhere around the periphery of the stem normal wood cells develop. Using methods presented in Archer (1987), it is possible to calculate the increment of new stresses in the entire stem due to the mechanical action of each new increment of growth. The associated deformation of the stem is also calculated.

A particular stem experiment is studied for which experiments were carried out by Sinnott (1952). Comparisons with the results of his experiments can only be qualitative since there are too many parameters which need to be estimated and which are not available. The purpose of the present work is to show the potential of this kind of analysis for problems where more quantitative data are available.

## Results

In one set of the many experiments with young trees of *Pinus strobus*, Sinnott (1952, Fig.3) pulled down the tree leader until the tip had undergone a rotation of 180° and was parallel to its basal portion (Fig.1). A tie held the tip^in this position. The xylem stresses and the bent shape shown in Fig.1 for the half loop were calculated using a theory for the elastic bending of tapered rods (Archer 1987). A simplified model for the compression wood (CW) action was
used. Growth increments each corresponding to 10% of the annual growth were added to the stem. If the newly developing wood in the cambial zone was adjacent to wood in compression, the CW cells are assumed to be formed and the resulting mechanical action of the CW will stress and deform the stem including the new layer of wood. Repeated application of these rules for CW induction provides an algorithm for the formation of CW according to the stess hypothesis. In Fig.3, typical stress distributions in newly grown layers (for layers 9 and 10, the last two layers in the annual growth) are presented.

A summary of the induction of CW based upon the stress hypothesis is given in Fig.2. A vertical section through the stem is made and the stem is shown as straight. Portions of growth layers shown as shaded represent CW. The initial compression zones at the periphery of the newly bent stem are indicated by lower case letters "c" (Fig.2). The experiments carried out by Sinnott (1952) result in CW located over the first 70% of the inside of the bent stem and then over the last 30% of the outside as shown by shading in Fig.1 and marked by arrows in Fig2.

According to the above analysis, starting with the initial compressive stress state in the newly bent stem on through most of the stress states induced in the new growth layers but CW action, there is a tendency to create CW in the general regions of the stem where Sinnott (1952) observed CW.

References

ARCHER, R.R. (1987). Growth stresses and strains in trees. Springer Verlag, 240p.

EWART, A.W. & MASON-JONES, A.J. (1906). The formation of red wood in conifers.
Ann. Bot. 20 : 201-204.

SINNOTT, E.W. (1952). Reaction wood and the regulation of tree form.

Am. J. Bot. 39 : 69-78

WILSON, B.F. & ARCHER, R.R. (1977). Reaction wood : Induction and mechanical action.

Ann. Rev. Plant Physiol. 28 : 23-43.

<figure><img src="image_31.png" /><figcaption>Figure 1 : Computed shape of a tapered tree pulled into a half loop and tied so that the tip is rotated through 180°. Shaded portions on the inside and outside correspond to CW induced in the trees (Pinus strobus) in the Sinnott (1952) 's experiments.</figcaption></figure>
<figure><img src="image_32.png" /></figure>

Figure 2: CW zones (shaded) as shown in a vertical section of the 100cm (straightened) stem. Growth before bending (normal wood) indicated by "+" while "*" indicates the 10 growth layers defined for purposes of analysis and occuring after the initial bending. The arrows indicate the limits of the CW zones as found by Sinnott (1952) for the inside and outside portions of the stem. [Note: CW results for growth layers 3,7 and 8 are interpolated from the calculated CW results for neighboring layers since computer results for those layers were found to be unreliable.]

<figure><img src="image_33.png" /></figure>

Figure 3. Typical bending stress increments induced in growth layers of a stem due to CW action in the layer. Results for layers 9 and 10 [The last two growth layers in the annual growth] are given.
WOOD STRUCTURE, CHEMICAL COMPOSITION AND GROWTH STRAINS
IN EUCALYPTUS CLONES.
INTERPRETATION OF THE NOTICED PHENOMENONS

H. BAILLÈRES(1); B. CHANSON(2); M. FOURNIER(2); M.T. TOLLIER(3); B. MONTIES(3)

(1) CIRAD-Forêt - 45 bis av. de la Belle Gabrielle - 94736 Nogent / Marne Cedex - FRANCE

(2) Laboratoire de Rhéologie du Bois de Bordeaux - BP 10 - 33610 Cestas Gazinet - FRANCE

(3) Laboratoire de Chimie Biologique (INRA) - 78850 Thiverval Grignon - FRANCE

The longitudinal residual growth strains at the stem surface, named Longitudinal Residual Strain of Maturation (LRSM), is appraised by stresses ("growth stresses") release on stem periphery by means of cutting in the wood [1], [4], [5]. The measurement of Longitudinal Residual Strain of Maturation allowed a continuous and quantitative classification of wooden samples coming from hybrid clones of *Eucalyptus* (Congo, Africa). This kind of measurements allows a mechanical identification of tension wood. In *Eucalyptus* species, it is not characterised by G-fibres, it can be however characterised by its growth strains [1].

The relationships between wood structure and mechanical properties were studied by ultrastructural (MicroFibril Angle = MFA) and chemical (quantitative investigation of the monomeric compound of lignines by thioacidolysis [6]).

The results presented in this study show :

* an important variation of the LRSM with high values, in spite of the weak eccentricity, the good verticality and the absence of G-fibre of our trees (Fig 1)

* a negative correlation between the level of the LRSM, the lignin content (Klason lignin) and the MFA (Fig 2 and 3)

* a positive correlation between the level of the LRSM and the ratio of the lignin monomeric units rates: syringyl on guaiacyl (S/G ratio) (Fig 4).

The weak knowledge about the effects of quantitative and qualitative variations of lignins on the phenomenons involve in physical and mechanical caracteristics of wood don't allow us an interpretation of this observation.

The signification of these correlations can be discussed as a biochemical problem: are there direct mechanical causality or more intricate correlations between structural variables ?

Some micro-mechanical models allow the expression of the longitudinal deformation of maturation at the scale of the cell wall in terms of two biochemical phenomenons (Fig 5 et 6) :

* The swelling of amorphous matrix typical of the lignification [3], the deposition of encrusting lignins between cellulose fibrils causes transverse expansion, because of the lateral links between fibrils, the transverse expansion is associated with longitudinal contraction.

* The contraction of the microfibrils typical of the crystallisation process of cellulose with simultaneous polymerisation due to a high degree of lateral order in the crystals [2].

BIBLIOGRAPHY :

[1] BAILLERES H., CHANSON B., FOURNIER M., TOLLIER M.T., MONTIES B., 1994. Structure, composition chimique et retraits de maturation du bois chez des clones d'Eucalyptus. Accepted by the *Annales des Sciences Forestières*.

[2] BAMBÈR R.K., 1987. The origin of growth stresses : A rebutal, *IAWA Bulletin n.s. 8(1)*, 80-84.

[3] BOYD J.D., 1985. The key factor in growth stress generation in trees : lignification or crystallisation. *IAWA Bulletin* 6(2), 139-150.

[4] FOURNIER M., CHANSON B., THIBAUT B., GUITARD D., 1994. Mesure des déformations résiduelles de croissance à la surface des arbres, en relation avec leur morphologie. Observations sur différentes espèces. *Ann. Sci. For.* 51(3), 10 p.

[5] FOURNIER M., GUITARD D., 1994. Les contraintes de croissance générées par la différenciation cellulaire. *Acta bot. Gallica* 140(4), 12 p.

[6] MONTIES B., 1991. *Lignins in Methods in Plant Biochemistry Vol. 1.* p 113-153. Harbone J.B. Ed.
<figure><img src="image_34.png" /><figcaption>Fig 1: values distribution of the LRSM (LRSM are shrinkages expressed here in absolute value)</figcaption></figure>

<figure><img src="image_35.png" /><figcaption>Fig 3: relationship between MFA of S2 layer and LRSM</figcaption></figure>

<figure><img src="image_36.png" /><figcaption>Fig 2: relationship between Klason lignin rate and LRSM</figcaption></figure>

<figure><img src="image_37.png" /><figcaption>Fig 4: relationship between S/G ratio and LRSM</figcaption></figure>

<figure><img src="image_38.png" /><figcaption>Fig 5: the origin of the longitudinal deformation of maturation at the scale of the cell wall can be expressed in terms of two biochemical phenomenons.</figcaption></figure>

<figure><img src="image_39.png" /><figcaption>Fig 6: Schematic representation of the mechanical and histological observations.</figcaption></figure>
TWO FIELD MEASUREMENT TECHNIQUES FOR APPRAISING THE LONGITUDINAL GROWTH STRAINS AT THE STEM SURFACE.

H. BAILLÈRES(1); B. CHANSON(2); M. FOURNIER(2)

(1) CIRAD-Forêt - 45 bis av. de la Belle Gabrielle - 94736 Nogent / Marne Cedex - FRANCE

(2) Laboratoire de Rhéologie du Bois de Bordeaux - BP 10 - 33610 Cestas Gazinet - FRANCE

Growth stresses originate in surface growth strains (= maturation strains), induced in cambial layers during the differentiation and maturation of new cells, impeded by the mass of the whole trunk. The longitudinal residual growth strains at the stem surface, named Longitudinal Residual Strain of Maturation (LRSM), is appraised by stresses ("growth stresses") release on stem periphery by means of cutting in the wood located under the cambium. This cutting is supposed to release locally, in the measured spot, existing stresses in the stem, and thus, the observed strains are proportional and have opposite signs to the initial stresses.

Two different methods using special sensors are used for the determination of the longitudinal residual strain of maturation :

1> The single drilled hole method, using CIRAD sensor (Fig 1). It's a classical technique for measuring residual stresses in elastic materials [1], [2], [3]. The metrological principle consists in measuring dimensional changes in fibre direction near a single drilled hole. The recorded value is a displacement (δ) that is proportional to the LRSM (αL) :

$$α_L = - \phi δ$$

where φ is a variable that depend on : hole diameter, reference distance of measurement, moduli of elasticity (E_L and E_T), shear modulus parallel to the grain (G_LT) and Poisson coefficient (ν_LT).

2> The two grooves method, using Wap's sensor (Fig 2). This method uses a classical extensometric sensor (manufactured by HBM - Germany) [2], [3], [4]. The total longitudinal stress is relieved by sawing two grooves above and below the sensor. After this operation we achieve the longitudinal residual strain of maturation.

In spite of the difference between the position of the measurement spots (it's impossible to realise two measurements on the same place), there is a highly significant correlation between the values achieved by the two methods (Fig 3).

BIBLIOGRAPHY

[1] ARCHER R.R., 1986. Growth Stresses and strains in trees. Springer Verlag, Springer series in wood science, Editor : E. Timell, 240 p.

[2] BAILLÈRES H., 1994. Précontraintes de croissance et propriétés mécano-physiques de clones d'Eucalyptus (Pointe Noire - Congo) : hétérogénéités, corrélations et interprétations histologiques. Thèse en Sciences du Bois de l'université de Bordeaux I, 161 p.

[3] FOURNIER M., CHANSON B., THIBAUT B., GUITARD D., 1994. Mesure des déformations résiduelles de croissance à la surface des arbres, en relation avec leur morphologie. Observations sur différentes espèces. Ann. Sci. For. 51(3), 10 p.

[4] FOURNIER M., GUITARD D., 1994. Les contraintes de croissance générées par la différenciation cellulaire. Acta bot. Gallica 140(4), 12 p.
<figure><img src="image_40.png" /><figcaption>Fig 1 : single drilled hole method
(CIRAD sensor)</figcaption></figure>

<figure><img src="image_41.png" /><figcaption>Fig 2 : two grooves method
(Wap's sensor)</figcaption></figure>

<figure><img src="image_42.png" /><figcaption>Fig 3 : correlation between the values achieved by the two methods
on *Eucalyptus* clones.</figcaption></figure>

For each point the sensors are situated on the same generatrix
with a distance of about 20 cm one from the other.
LODGING : THE DEVELOPMENT OF A RISK ASSESSMENT TECHNIQUE
BASED ON A MECHANICAL MODEL

C.J.BAKER

Dept. of Civil Engineering, University Park, Nottingham,
NG7 2RD, UK

J.M.GRIFFIN & R.K.SCOTT

Dept. of Agriculture & Horticulture, Sutton Bonington Campus,
University of Nottingham, Loughborough, LE12 5RD, UK

R.SYLVESTER-BRADLEY

ADAS Soil & Water Research Centre, Anstey Hall, Cambridge,
CB2 2LF, UK

Lodging is a serious problem for cereal growers and when extensive lodging occurs in seasons such as 1980, 1985, 1987 and 1992, costs to the industry are large, through lower yields and poor grain quality.

Our aim is to reduce lodging and in order to achieve this, the development of a better predictive system of lodging risk in wheat is of paramount importance. The vast majority of lodging is caused by two basic modes of failure; buckling at the stem base or uprooting in the soil. The basis of the prediction system evolves around a mechanical model which encompasses both of these types of lodging.

The model outlined for wheat consists of a double 'lumped mass' (representing the ear and the root ball respectively) on a weightless stem (see Fig. 1), which forms a two degree of freedom system. Preliminary calculations to determine the transfer functions for the system indicate that the model can be simplified to a one degree of freedom system, which is assumed to act as a second order harmonic oscillator. Wind engineering technology was used to formulate the model. In simple terms, the model describes how the transfer functions can be used to form a spectrum of base bending moment of a wheat stem. From the incident wind spectrum values for the extreme base bending moment can then be extrapolated, in order to determine the plants failure criteria.

The ultimate objective is to develop a method of identifying individual wheat crops at high risk then to control lodging at least cost. Experimentally, this will involve the measurement of various parameters in the spring, which include identification of loose tilth, or weakly binding soil, few or weak roots, thin or weakened stems and the potential for dense wind- and rain-trapping canopies and heavy heads. If these measurements can be shown to predict vulnerability in July (when highest lodging risk occurs), as a result of fulfilling the failure criteria derived from the model, then the percentage probability of lodging occurring can be predicted. If anchorage is thought at fault then the best option may be to roll the crop. If stem buckling is expected then a plant growth regulator can be applied or less nitrogen fertilizer can be used, to control lodging.
<figure><img src="image_43.png" /><figcaption>Fig. 1 - *The basic mechanical model of a wheat stem*</figcaption></figure>

References

BAKER, C.J. (1993) Engineering approaches to aspects of the wheat lodging problem.
*Nottingham University, Dept. of Civil Engineering, Report Number FR93036*.

EASSON, D.L., WHITE, E.M. and PICKLES, S.J. (1992) A study of lodging in cereals.
*Home-Grown Cereals Authority, Report Number 52*.

ENNOS, A.R. and CROOK, M.J. (1993) The mechanics of root lodging in winter wheat,
*Triticum aestivum L. Journal of Experimental Botany 44*, 1219-1224.

FINNIGAN, J.J. (1979) Turbulence in waving wheat I and II. *Boundary-Layer Meteorology* **16**, 2, 181-236.

GRAHAM, J. (1983) Crop lodging in British wheats and barleys. PhD thesis, Reading University.
PATTERNS AND PROGRAMS OF CELL DIVISION IN ROOT MERISTEMS OF MAIZE AND TOMATO

P W Barlow¹, J Lück² and HB Lück²

¹Dept of Agricultural Sciences, University of Bristol, Long Ashton Research Station, Bristol BS18 9AF, UK, ²Laboratoire de Botanique analytique et Structuralisme végétal, Faculté des Sciences et Techniques de St-Jérôme, 13397 Marseille cedex 13, France.

Besides their importance as units of growth and differentiation, cells, by virtue of their turgidity and the rigidity of their walls, are units of structural support for plant tissues and organs. Presumably, the network of cell walls (cellworks)¹, which can be seen in histological sections, has evolved to provide an optimal internal scaffold for the maintenance of form and the differentiation of metabolic functions. In the root, most of this cellwork results from the continuous growth and division of cells within the apical meristem. We have found that relatively simple algorithms will develop the cellworks seen within the meristem of maize (Zea mays L.) roots and attempts are being made to extend these algorithms to account for the cellworks of the tomato (Lycopersicon esculentum Mill.) root apex.

In the primary root of maize, the distal part of the meristem maintains a recurrent pattern of periclinal, longitudinal-radial, and anticlinal divisions (formative divisions) which develops the basic cellwork. In the proximal (and major) part of the meristem the cellwork expands and shows ordered sequences of anticlinal divisions (proliferative divisions). We analysed in detail the relative elongation growth and sequence of mitoses of cells participating in the first four rounds of division following germination²,³ and, in a more general way, the relative lengths of cells resulting from two further rounds of division. In this post-germination period it was possible to recognize cell packets (groups of cells of common descent) containing from 1 to 16 cells and, later, up to 64 cells. At this latter stage, many cells were then emigrating from the meristem into the non-meristematic elongating zone.

Although a large number of division pathways are theoretically possible, each pathway being defined by a particular sequence of divisions within a growing packet, observation shows that relatively few are actually used². This suggests that there may be some inherent polarity of growth or division which limits their number. In fact, the pathways that do operate result from inherited sequences of asymmetric division that lead to sister cells of unequal length. However, as root growth proceeds the asymmetry becomes less noticeable. The unequal divisions are a regular feature of the germinating primary root. Their significance is obscure; divisional asymmetry may have some consequence for countering the physical resistance that roots experience as they penetrate the soil, or it could ensure that cell cycle phases are asynchronous and thereby minimizes the sensitivity of the cell population to potentially damaging effects from the environment. Asymmetry may even, in some way, anticipate further cell differentiation⁴: viz. the case of trichoblasts, for example.

All possible pathways, not just those actually found, can be generated by deterministic 'bootstrap' L-systems which assign different lifespans to sister cells of successive generations and hence specify the sequence of divisions². The two pathways most frequently found in the maize root meristem are shown in Fig. 1. Further analysis has shown that these minimal pathways can be expanded (Fig. 2) to represent the division pattern occurring later in development, following which the cell packets pass from the meristem into the elongation zone. At the same time, the relative values for the lifespans can be related to those described earlier⁵ and by more direct analysis from the kinetics of ³H-thymidine-labelled mitoses⁶.

Programmes of formative divisions have been further investigated in clones of *in-vitro*-grown tomato roots and have provided material for studies of cell genealogies in the three major histogenetic zones of stele, cortex and cap/epidermis⁷. The lifespans and genealogies
<figure><img src="image_44.png" /></figure>

Fig. 1. Genealogical trees illustrating two cell populations simulated by a bootstrap device which follow (a) pathway P₁₄ and (b) pathway P₂₁, these two pathways being the most frequent in the early stages of cell development in the meristem of the maize root cortex.

Fig. 2. Genealogical tree illustrating pathway P<sub>E2</sub>, this being a pathway that represents cell growth and division as cells migrate through the proximal part of the meristem.

of each cell in each histogen are coordinated, the genealogy of the cap being the most complex and its development is related to the genealogy of the cortex. For analytical purposes, the cap is considered as being sub-divided into three zones: a central columella, a flank zone that extends up the side of the root and abuts the outer face of the cortex, and an intermediate zone wedged between these other two zones. The fate of each cell in each zone can be traced both spatially and temporally, from its inception by a functional initial cell until it 'dies' and is shed from the surface of the root. Remarkably, cells from each zone of the cap are shed simultaneously as a coherent peel of senescent tissue, all cells having the same age since their birth from an initial.

Again, three types of formative division initiate the cellwork of the cap and each type can be mapped to specific sites in each zone. The columella zone, however, is constructed from transverse divisions only. Zones change their boundaries as the root grows. For example, the columella zone increases its diameter at a rate of 1 new cell-file being added every 4.5 days, or in the time that 1.8 cells are added to a pre-existing columella cell-file. The new files are derived from initials in the former intermediate zone; their diverse types of division give way to transverse only, this being brought about by radial growth of the cortical tissue.

Algorithms are being constructed that will formalize the coordinated development of all three histogens and the divisional lifespans of their component cells.

## References

1. Liu, H.L. & Fu, K.S., 1981. *Information Sciences* 24, 93-109.

2. Lück, J, Barlow, P.W. & Lück, H.B., 1993. *Cell Proliferation* 27, 1-21.

3. Lück, J, Barlow, P.W. & Lück, H.B., 1993. *Annals of Botany* 73, 1-11.

4. Barlow, P.W., 1984. In *Positional Controls in Plant Development* (eds P.W. Barlow & D.J. Carr), pp. 281-318 Cambridge University Press, Cambridge.

5. Barlow, P.W. & Macdonald, P.D.M. (1973). *Proceedings of the Royal Society B* 183, 385-398.

6. Barlow, P.W., 1987. *New Phytologist* 105, 27-56.

7. Barlow, P.W., 1993. In *Molecular and Cell Biology of the Plant Cell Cycle* (eds J.C. Ormrod & D. Francis), pp. 179-199. Kluwer Academic Publishers, Dordrecht.
STRUCTURAL BASIS FOR THE BIOMECHANICAL BEHAVIOUR OF
RATTAN MATERIAL

K. M. Bhat

Division of Wood Science

Kerala Forest Research Institute

Peechi 680 653

India

With the recent concept of property manipulation in wood and non-wood forest products, rattans - the climbing palms of the tropics will soon find a place in material science. Rattan competes with numerous other materials like wood, plastics and metals. As a material, its versatility is evident from the unique aesthetic value of its furniture products, high strength to weight ratio, durability, ease in workability, pliability, bio-degradability and natural renewability as crop. Based on the study of more than 25 species of Indian rattans, representing three genera, viz. *Calamus*, *Daemonorops* and *Korthalsia*, attempts are made in this paper to establish the definite structure-property relationships to interpret the biomechanical behaviour of rattans.

Based on the mechanical properties such as bending (modulus of rupture - MOR) and tensile stresses (UTS), three classes recognised are: (a) strong to very strong (MOR and UTS > 70 N/mm²), (b) moderately strong (45-70 N/mm²) and (c) weak (< 45 N/mm²) rattans. With the MOR of 65 N/mm², the average bending strength of rattans is close to that of wood (65.5 N/mm²) or even greater than that of bamboo (55 N/mm²) although the maximum compressive stress (parallel to grain) is low (28 N/mm²).
With the greater range of mechanical property values, rattan appears to be more heterogeneous material than wood. This is possibly due to the different pattern of structural variability at the tissue/cellular level as evident from the following:

- The mechanical tissues (sclerenchyma fibres), confined to the scattered vascular and non-vascular bundles, generally account for only 1/3rd of the total stem tissues of rattans in contrast to the relatively high fibre content of wood.

- The percentage of fibres within the vascular bundles and the polylamellate fibre wall thickness show more definite patterns of variation than the vascular bundle size and number per unit area.

- Instead of fibres, non-mechanical cortical and ground parenchyma constitute as the major component (up to 58-60%) of stem tissues.

- The conducting tissues viz. xylem and phloem often contribute to 30-35% void volume of the material.

- At the ultrastructural level, it is observed that new lamellae are added with the aging of fibres, thereby increasing both the wall thickness and density of the material.

- The fibre wall structure/thickness appears to be the single most important factor that determines the mechanical behaviour under bending and tensile stresses. The fracture mode of individual fibres follows the fibril angle and is in opposite direction from broad to narrow lamellae. The broad lamellae appear to govern the fracture behaviour more than the narrow lamellae.
# REGULATION DE LA FORME DU TRONC DE PINUS KESIYA DANS LA REGION DU MANGORO (MADAGASCAR): INDEPENDANCE ENTRE LA FORME DE LA SECTION DROITE ET LA COMPETITION INTER-INDIVIDUS

JP Bouillet, Mission CIRAD-Forêt, BP 745, Antananarivo, Madagascar

## INTRODUCTION

L'impact des éclaircies fortes et précoces sur les *Pinus kesiya* du Mangoro (≈ 50000 ha) est connu: très forte réaction individuelle sans modifications notables des propriétés technologiques du bois (mesurées sur des éprouvettes sans défaut, ni bois de compression). Mais pour donner un avis définitif sur l'effet d'une telle sylviculture sur la qualité des arbres, on doit aussi connaître l'influence des éclaircies sur l'anisotropie radiale, qui entraîne la production de bois de moins bonne qualité technologique.

C'est pourquoi une étude a été engagée pour répondre aux questions suivantes:

- les éclaircies entraînent-elles une activité cambiale plus importante dans la direction des arbres partant en éclaircie, sous l'hypothèse avancée par ZIMMERMANN et BROWN (1971) d'un flux vertical de sève élaborée avec peu de transferts latéraux?

- est-il possible de proposer un schéma de régulation de la forme du tronc?

## RÉSULTATS

*Caractérisation de l'irrégularité d'une section et de son évolution au cours du temps*

Celle-ci repose sur l'identification des accroissements radiaux annuels à des vecteurs et sur l'évolution de leur somme.

*Effet de la compétition aérienne sur l'anisotropie radiale*

L'échantillon comporte 56 individus dominants/codominants âgés de 14 à 20 ans: 21 arbres témoins et 35 ayant subi 1, 2 ou 6 éclaircies pour lesquels sont construits 10 indices de libération de la concurrence qui tiennent compte de l'orientation des arbres enlevés en éclaircie. De 4 à 11 niveaux sont pris en compte par individu (limite du tronc: diamètre fin bout de 15cm sur écorce).

On aboutit aux résultats suivants: (1) l'orientation de l'excentricité ne dépend pas de celle des voisins enlevés en éclaircie, (2) l'amplitude de l'excentricité, assez marquée, est comparable pour les arbres témoins et ceux enlevés en éclaircie, (3) l'excentricité est globalement orientée le long du tronc dans une direction NW, (4) une forme de la section bonne prédictrice de la forme finale apparaît précocement (3-5 ans), (5) le méplat ne présente pas d'orientation privilégiée et est assez marqué.

*Correspondance excentricité et distribution des branches le long de l'axe principal*

Afin de préciser les résultats précédents, on a étudié la correspondance pouvant exister entre l'excentricité et la distribution (orientation et grosseur) des branches le long de l'axe principal. L'étude a porté sur 54 individus âgés de 5 à 22 ans et a pris en compte 2 types de correspondance (stricte ou sur une partie limitée du périmètre) et 2 types d'influence des branches (locale ou sur une longue distance).

On observe que: (1) l'excentricité des sections ne dépend pas de la distribution des branches le long de l'axe principal, tant pour le tronc que pour la partie sommitale de l'arbre,
correspondant au houppier participant de manière prépondérante à la croissance,

(2) l'excentricité est toujours globalement orientée vers le NW.

L'étude complémentaire de 14 individus élagués sur la moitié de leur périmètre, et ceci sur toute leur hauteur, conduit aux mêmes conclusions.

### Causes possibles

Les phénomènes ne peuvent être expliqués par :

- une disposition particulière du système racinaire,

- des conditions spéciales au Mangoro; les mêmes observations sont faites sur *Pinus kesiya* à Manankazo,

- une caractéristique propre à *Pinus kesiya*; au Mangoro, *Pinus caribaea* est excentré aussi dans une direction NW.

L'influence des températures n'a pas été testée mais est une cause peu probable.

Le vent semble être la cause principale car: (1) le vent souffle de SE-->NW au Mangoro et à Mankazo (régime des alizés), (2) une excentricité se développant sous le vent d'intensité, comme au Mangoro, faible à modérée s'observe sur d'autres résineux et dans d'autres pays, (3) du bois de compression est noté dans la direction de l'excentricité.

## CONCLUSION - SCHÉMA DE RÉGULATION

On ne peut véritablement définir le chemin suivi par le flux de sève élaborée et plus généralement la connaissance de celui-ci ne suffit pas pour expliquer les phénomènes observés. L'alimentation du cambium semble sous la dépendance de relations de type source-puits, la partie N-W du tronc jouant le rôle d'un puits attirant de manière préférentielle les nutriments. L'excentricité du tronc est expliquée principalement par l'influence des alizés du S-E bien que leur intensité soit faible à modérée.

Un schéma de régulation de la forme du tronc est proposé (d'après LOUP *et al.*, 1991, modifié): les arbres réagissent de manière continuelle à l'action du vent de SE pour maintenir la forme de consigne, droite, en formant du bois de compression et des cernes plus larges dans la direction opposée au vent.

<figure><img src="image_45.png" /></figure>

LOUP, FOURNIER, CHANSON, 1991. Relations entre architecture, mécanique et anatomie de l'arbre - Cas d'un pin maritime. In: L'arbre, Biologie et Développement (EDELIN éd.) ZIMMERMANN, BROWN, 1971. Trees structure and function. Berlin: Springer

**Mots-clés:** forme des arbres, éclaircies, fonctionnement du cambium, *Pinus kesiya*
# FINITE ELEMENT ANALYSIS OF THE MECHANICAL PROPERTIES OF PLANT CELLS

K.M. BURROWS

UNILEVER RESEARCH LABORATORY
COLWORTH HOUSE
SHARNBROOK
BEDFORDSHIRE MK44 1LQ

During standard materials testing, assumptions such as material continuity, isotropy and homogeneity are generally made. When testing biological materials these assumptions are not valid due to the cellular nature of the tissue. As a result of this, a structural analysis is necessary.

It is difficult to relate the stress or strain applied to the tissue sample to the stress in the cell-wall. Models are needed to give relations between the properties of the material and the properties of individual cell components. A number of models have been developed, most use analytical techniques to define the relationship between cell-wall properties and turgor pressure, and the gross mechanical properties of the tissue. [1-3]

Finite element techniques hold out the promise of modelling the structure of fruits and vegetables using reasonable materials constants to model the type of behaviour expected from plant tissue under general mechanical loading. It should be possible to include the effects of varying cell size, shape and wall thickness in the calculation of the response of the tissue to external loading.

Current finite element techniques use software packages that model either solids or fluids. In modelling plant tissue, we need to combine the behaviour of a solid with that of a fluid. In this poster we examine the behaviour of a single, fluid-filled cell under compressive, flat plate loading. For simplicity, the cell-wall and cell fluid are assumed to be homogeneous and isotropic during the current investigation. The presence of cell fluid is modelled using two different techniques. One method involves representing the fluid as a solid with fluid-like properties; in the other the fluid is represented as a pressure load normal to the internal surface of the cell-wall, with compression taking place at constant cell volume. The relative merits of the two techniques are considered and assessed.

[1] R.S. GATES, R.E. PITT, A. RUINA AND J.R. COOKE. Cell Wall Elastic Constitutive Laws and Stress-Strain Behaviour of Plant Vegetative Tissue. *Biorheology*, **23**, 1986, 453-466.

[2] Q. GAO, R.E. PITT AND A. RUINA. A Mechanics Model of the Compression of Cells with Finite Initial Contact Area. *Biorheology*, **27**, 1990, 225-240.

[3] Q. GAO, R.E. PITT. Mechanics of Parenchyma Tissue Based on Cell Orientation and Microstructure. *Transactions of the ASAE*, **34**, 1991, 232-238.
AUTOPORTANCE vs NON AUTOPORTANCE: SES EXPRESSIONS ANATOMIQUES ET MORPHOLOGIQUES CHEZ LES LIANES.

Guy Caballé et Francis Hallé

Ecole Pratique des Hautes Etudes, Laboratoire de Botanique, 163 rue Auguste Broussonnet, 34000-Montpellier, France.

Les lianes tropicales réalisent des ontogenèses anatomiques variées. Cette radiation anatomique dans le groupe des lianes est la conséquence directe de l'accomplissement d'une gamme étendue de processus de croissance secondaire.

Dans leurs phases expansives de développement en forêt, les lianes tropicales adoptent un mode de vie non autoportant et grimpant. Juvéniles, contraintes ou piégées dans un environnement ouvert, ces mêmes lianes prennent de préférence un mode de vie autoportant. Cette dualité de mode de vie est toujours sous-jacente, même si elle peut être très affirmée chez certaines espèces et familles (ex. Connaraceae et Dichapetalaceae) ou au contraire plus diffuse chez d'autres (ex. Mimosaceae).

Le passage d'un mode de vie à l'autre s'accompagne le plus souvent de transformations biomorphologiques radicales, rapides et durables: principalement en anatomic, architecture et morphologie, dynamique de croissance et physiologie. Les changements anatomiques sont à la fois qualitatifs et quantitatifs, d'ordres structurel et fonctionnel: nouveaux modes de fonctionnement du cambium, néoformation d'assises cambiales, fractionnement de la charpente primaire, assemblage des tiges en plusieurs cylindres, richesse accrue en fibres, réduction des tissus de soutien, fort développement des parenchymes, augmentation sensible des dimensions des vaisseaux conducteurs, etc. Les études de terrain révèlent que c'est à partir du moment où les lianes ne se conforment plus à un mode de vie autoportant que leur énorme potentiel de diversité anatomique s'extériorise le mieux.

Sur un plan évolutif, les lianes pourraient représenter une forme ligneuse particulière qui aurait conservé (ou acquis) deux modes de vie, un autoportant, l'autre non. Dans ses exemples les plus représentatifs, l'intégration anatomie-mode de vie serait parfaite: une dualité anatomique correspondrait à la dualité des ports. Ailleurs, la diversité des situations et tendances s'inscrirait dans un large continuum. Quelques rares exemples d'espèces arborescentes qui ont la possibilité de modifier leur port ou leur maintien mériteraient une étude approfondie.

**Bibliographie sommaire:**

-Bhambie S. 1972. Correlation between form, structure and habit in some lianas. Proc. Indian Acad. Sci. 75(5): 246-256.

-Caballé G. 1986. Sur la biologie des lianes ligneuses en forêt gabonaise. Thèse de Doctorat d'Etat, Université de Montpellier II Sciences et Techniques du Languedoc.

-Caballé G. 1993. Liana structure, function and selection: a comparative study of xylem cylinders of tropical rainforest species in Africa and America. Bot. J. Linn. Soc. 113(1): 41-60.
- Chiu S.-T. & F.W. Ewers 1992. Xylem structure and water transport in a twiner, a scrambler, and a shrub of *Lonicera* (Caprifoliaceae). *Trees* **6**: 216-224.

- Coudurier T. 1992. *Sur la place des lianes dans la forêt guyanaise. Une approche qui utilise l'architecture végétale*. Thèse de Doctorat, Université de Montpellier II Sciences et Techniques du Languedoc.

- Cremers G. 1973. Architecture de quelques lianes d'Afrique Tropicale. 1. *Candollea* **28/2**: 249-280.

- Cremers G. 1974. Architecture de quelques lianes d'Afrique Tropicale. 2. *Candollea* **29/1**: 57-110.

- Ewers F.W. 1985. Xylem structure and water conduction in conifer trees, dicot trees, and lianas. *IAWA Bull. 6(4)*: 309-317.

- Gartner B.L. 1991. Is the climbing habit of poison oak ecotypic? *Funct. Ecol.* **5**: 696-704.

- Gasson P. & D.R. Dobbins 1991. Wood anatomy of the Bignoniaceae, with a comparison of trees and lianas. *IAWA Bull. 12(4)*: 389-417.

- Givnish T.J. & G.J. Vermeij 1976. Sizes and shapes of lianas leaves. *Am. Nat.* **110**: 743-778.

- Lee D.W. & J.H. Richards 1991. Heteroblastic development in vines. *In*: Putz F.E. & H.A. Mooney eds. *The Biology of Vines*. Cambridge University Press, pp. 205-243.

- Putz F.E. 1984. The natural history of lianas on Barro Colorado Island, Panama. *Ecology* **65**: 1713-1724.

## Coupes transversales de tiges de lianes:

Les parties en noir uni correspondent aux phases autoportantes.

1. *Millettia duchesnei* 2. *Machaerium leiophyllum* 3. *Strychnos* sp. 4. *Icacinaceae*.

5. *Griffonia physocarpa*. 6. *Anacolosa uncifera*. 7. *Uncaria africana*. 8. *Salacia* sp.

9. *Salacia staudtiana*. 10. *Verbenaceae*. 11. *Loeseneriella clematoides*.

<figure><img src="image_46.png" /></figure>

4

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6

<figure><img src="image_48.png" /></figure>

9

<figure><img src="image_49.png" /></figure>

11

<figure><img src="image_50.png" /></figure>

3

<figure><img src="image_51.png" /></figure>

7

1cm

<figure><img src="image_52.png" /></figure>

1

<figure><img src="image_53.png" /></figure>

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10
# CHANGES IN LIGNIFICATION IN ROSE FLOWER PEDUNCLES DIFFERING BY THEIR RESISTANCE TO BENDING

B Chabbert, B Monties

Laboratoire de Chimie Biologique, INRA, INA-PG, 78850 Thiverval Grignon, FRANCE

N Zieslin, R Ben-Zaken

The Hebrew University of Jerusalem, Faculty of Agriculture, PO Box 12, Rehovot, 76-100 ISRAEL

Bending of rose stems (bent-neck) during ageing is one important characteristic determining the post-harvest quality of rose peduncles (1). The tendency to bend is dependent on cultivar and stage of flower bud development. The upper part of the peduncles further shows the least resistance to bending as compared to basal part (2).

Anatomical differences have been reported between the strong flower peduncles of cv. Mercedes and the weak peduncles of cv. Nubia (3). The resistance to bending has also been related to highest peroxidase activity in strong cultivar(4). Peroxidases are implicated in various plant processes among which polymerisation of cinnamyl alcohol polymerisation into lignin. Apart from others functions, lignin in association with the cell wall components is assumed to contribute to the cell wall rigidity and plant support (5).

Both quality and quantity of lignin polymer displays large variations under genetic and physiological factors (6). These changes are mainly correlated to the variations in:

- proportions of the main monomers, syringyl and guaiacyl corresponding to the di- and monomethoxylated units,

- frequency and nature of intermonomeric linkages, the alkyl aryl ether bonds referred to non-condensed ones are prominent as compared to the C-C linkages (condensed).

This study was designed to evaluate the possible variations in lignification in relation to the resistance of bending of peduncles from strong cultivar (cv. Mercedes) and weak cultivar (cv. Nubia). Monomeric composition of lignin was determined by depolymerisation of the phenolic network using thioacidolysis (7) which allows specific determination of the non-condensed monomeric units.

Largest changes in lignin content were observed in xylem tissues as compared to phloem tissues. Upper parts of both cultivars and tissues of the weak cultivar are less lignified (figure 1). Lignin from phloem and xylem of cv. Mercedes contains larger amounts of non-condensed structures than corresponding tissues of the weak peduncle. In addition, enriched syringyl lignin fractions are deposited in the stronger peduncles, especially in the distal parts (table 1 & 2).

The variations observed in content and composition of lignin from strong and weak peduncles suggest that lignin may have a tissue specific function in the resistance of these cultivars to bending (8). Such modifications under genetic control might also be related to specific syringyl deposition in secondary wall differenciation of fiber cells, regarded as the main supporting cells in plants.

1-Burnett A N (1970) J. Am. Soc. Hort. Sci. 95: 427-431.

2-Zieslin N, Starkman F & Zamski E (1989) Pl. Growth Regul. 8: 65-67.

3-Zamski E, Starkman F & Zieslin N (1991) Israel J. Bot. 40: 1-6.

4-Zieslin N & Ben-Zaken R (1991) Pl. Physiol. Biochem. 29: 147-151.

5-Lewis N G & Yamamoto E (1990) An. Rev. Pl. Physiol. Pl. Molec. Biol. 41: 455-496.

6-Monties B (1989) Methods in Plant Biochemistry 1: 113-145.

7-Lapierre C, Monties B & Rolando C. (1986) Holzforschung 40: 113-119.

8-Chabbert B, Monties B, Zieslin N & Ben-Zaken R (1993) Plant Physiol. Biochem. 31: 241-247.
<figure><img src="image_57.png" /><figcaption>Table 1: MONOMERIC COMPOSITION OF LIGNIN FROM XYLEM CWR IN ROSE PEDUNCLE (as µ mole G or S / g⁻¹)</figcaption></figure>

<table><caption>Table 2: MONOMERIC COMPOSITION OF LIGNIN FROM PHLOEM CWR IN ROSE PEDUNCLE (as µ mole G or S / g⁻¹)</caption><thead><tr><th>Part of the peduncle</th><th>Cultivar</th><th>Guaiacyl<br>G</th><th>Syringyl<br>S</th><th>Total<br>S+G</th><th>Ratio<br>S/G</th></tr></thead><tbody><tr><td rowspan="2">Basal</td><td>Nubia</td><td>306 +/- 4</td><td>453 +/- 2</td><td>759 +/- 6</td><td>1.48</td></tr><tr><td>Mercedes</td><td>432 +/- 25</td><td>745 +/- 46</td><td>1177 +/- 71</td><td>1.70</td></tr><tr><td rowspan="2">Distal</td><td>Nubia</td><td>96 +/- 12</td><td>75 +/- 7</td><td>171 +/- 19</td><td>0.78</td></tr><tr><td>Mercedes</td><td>266 +/- 16</td><td>580 +/- 34</td><td>846 +/- 50</td><td>2.18</td></tr></tbody></table>

<table><thead><tr><th>Part of the peduncle</th><th>Cultivar</th><th>Guaiacyl<br>G</th><th>Syringyl<br>S</th><th>Total<br>S+G</th><th>Ratio<br>S/G</th></tr></thead><tbody><tr><td rowspan="2">Basal</td><td>Nubia</td><td>53 +/- 4</td><td>93 +/- 7</td><td>146 +/- 11</td><td>1.75</td></tr><tr><td>Mercedes</td><td>152 +/- 8</td><td>253 +/- 4</td><td>405 +/- 12</td><td>1.66</td></tr><tr><td rowspan="2">Distal</td><td>Nubia</td><td>14 +/- 4</td><td>11 +/- 2</td><td>25 +/- 6</td><td>0.78</td></tr><tr><td>Mercedes</td><td>25 +/- 2</td><td>66 +/- 6</td><td>91 +/- 8</td><td>2.64</td></tr></tbody></table>
# Influence of the inhomogeneity of the apple on the response spectra during nondestructive acoustic sensing of fruit firmness

H. Chen, F. Duprat, M. Grotte, D. Loonis, E. Pietri

INRA-LAMPE, Domaine Saint Paul, B.P.91, 84143 Montfavet, France

## Introduction

Nondestructive acoustic sensing of fruit firmness has been based on the derivation of the resonant frequency from the response spectrum of the fruit under vibration. The frequency is used in the stiffness factor $f^2m^{2/3}$, with f the resonant frequency and m the fruit mass, for the firmness evaluation. The reliability of this technique depends on whether a representative frequency can be correctly obtained. The response spectrum of an apple is influenced by some factors such as the shape and the inhomogeneity of the apple. The objective of this work is to investigate the influence of the inhomogeneity on the frequency spectrum.

## Experimental technique

Several Granny apples recently harvested and imported from Chile were used. The apples were first measured for their frequency response spectra and mode shapes. The reagent HCl of 18% Vol. was then injected into different parts of the apples to create the internal defects. Thirty minutes to two hours after the injection, the apples were measured again for their frequency spectra and mode shapes.

As shown in Fig.1, 20 points around the equator of each apple were measured. The apple was excited by impact at point 1. Two small condense type MCE-2500 microphones, with one fixed at point 1 and another placed in sequence from point 1 to 20, were used to measure the response signals. The signals were then fed into a Nicolet-310 digital oscilloscope which was connected via an IEEE-488 interface to a SX386 personal computer where the time-domain signals were transferred into the frequency spectra by using a program coded in Quick Basic. All the spectra were saved and further calculated in the same way as used by Huarng et al. (1992) for mode shapes.

## Results

Fig. 2 shows three spherical mode shapes measured for Granny apples, where the dotted circles represent the base circles and the solid lines the mode shape at one extreme deformation of the apple equator. The mode (a), (b) and (c), having respectively 2, 3 and 4 nodal lines, are referred to as $S_{20}$, $S_{30}$ and $S_{40}$. In previous research, the $S_{20}$ mode was found the most important in reflecting the fruit firmness, and its resonant frequency was therefore used in the stiffness factor $f^2m^{2/3}$ for calculating the fruit firmness.

Fig. 3(a) shows the frequency response spectrum of an apple without internal defect. The highest peak around 700-760 Hz corresponds to the $S_{20}$ mode, the peak around 1120-1140 to the $S_{30}$ mode and the peak around 1460-1480 Hz to the $S_{40}$ mode. Thirty minutes after 0.88g of HCl was injected into a part of the core, about 2.5% of the total weight of the apple in this region became very soft. In this case, the highest peak in Fig.3(a) is split into two peaks with one at around 580 to 600 Hz and another around 720 to 760 Hz (Fig.3(b)). Both peaks correspond to the $S_{20}$ mode. Using the lower frequency in the stiffness factor may cause an error of about 25 to 30% in firmness evaluation.

In comparison with the first apple, another apple was injected with half amount of HCl at an outer layer, which causes the same effect. It seems that the inhomogeneity in the outer part of an apple influences more on the response spectrum.

It was observed that some apples after a few months of storage display more peaks. This could probably be an indication of the existence of the inhomogeneity inside the apple.
## Conclusions

Inhomogeneity inside the apple may split the main resonant peaks in the frequency spectrum into two or even more, this may cause considerable error in the firmness evaluation. On the other side, the increase in the peaks during the storage of the apple can possibly be used as an indication of the internal defect.

<figure><img src="image_58.png" /><figcaption>Fig.1 Relative positions of the impact, microphones and 20 measurement points along the equator of an apple</figcaption></figure>

<figure><img src="image_59.png" /><figcaption>Fig.2 Spherical mode shapes of the apple</figcaption></figure>

<figure><img src="image_60.png" /></figure>
Predictability of leaf toughness from anatomical studies

Ms Mei Fun Choong

Botany Department,
University of Hong Kong,
Pokfulam Road,
Hong Kong

Toughness, a term which is here used to mean the work required to make unit area of
crack, has been postulated to be one of the mechanisms that a plant uses to defend its
leaves against herbivores. There is, however, little agreement in the ecological literature
over the definition of leaf toughness (most authors consider it to be the force required to
push a rod through the lamina) and also about what causes it - various suggestions
include the presence of silica, the thickness of the cuticles and the proportion of lignin in
the cell wall. In addition, toughness is often confused with stiffness - increasing the
stiffness of a leaf may aid its photosynthetic function. This study is designed (a) to
attempt to determine which parts of a dicotyledonous leaf provide it with toughness, (b)
to use this information to predict the toughness of other leaves and (c) to establish
whether the distribution of tough tissue is optimal to defend leaves from herbivores or
instead to act in some other capacity, such as to prevent wind damage, for example.

The anatomy of the leaf of *Castanopsis fissa* (Fagaceae) was studied as part of a wider
investigation into the leaf structure of the oak family in relation to herbivory. This leaf
has been observed being eaten by herbivores external to the leaf and also by those living
inside it (leaf miners). Using confocal images, the relative thicknesses of the layers of the
leaf - upper and lower epidermis, palisade, spongy mesophyll, vascular tissue (both
xylem and phloem), sclerenchyma bundle sheath and also the parenchyma bundle sheath
extension - were estimated. In addition, anatomical features of the cell wall thickness and
cell shape were quantified. A distinction was made between heavily-lignified on the one
hand and lightly- or non-lignified tissue on the other, lignification being judged both by
natural fluorescence and by phloroglucinol staining. These measurements have been
manipulated into an index which could predict the toughness of a leaf and which could
also help to estimate the energy expended by an invertebrate herbivore in feeding on
various tissue layers of the leaf.
RELATIONSHIPS BETWEEN TREE MORPHOLOGY AND
LONGITUDINAL GROWTH STRESS MEASURED AT STEM LEVEL:
INSTANCE OF PIN MARITIME (*Pinus pinaster* Ait.).

COMBES J.-G.

Laboratoire de Rhéologie du Bois de Bordeaux - B.P. 10 - 33610 Cestas Gazinet - FRANCE.

During tree growth, two major accidents can happen inducing some after-effects on
morphogenesis:

- a change of the tree initial orientation involving the recovery of the growth direction by a stem deformation, in case studied a basal sweep (Fig. 1).

- a loss of apical dominance involving the putting of a traumatic reiteration complex under fork appearance (Fig. 2).

In any cases, there will be an elaboration of typical wood (reaction wood named compression wood in gymnosperms and tension wood in angiosperms) in peculiar angular sector of stem. This wood presence allows a reorientation movement of the stem, sometimes important. Peripheral measurements of Longitudinal Residual Strain of Maturation (LRSM) show a strain peak associated with the presence of réaction wood.

After cambial division, daughter cells go into a differenciation and maturation stage. During the formation of secondary wall, cells have a tendency to shrink longitudinally (and to swell tangentially) but the presence of anciently formed and rigid cells prevent this shrinkage. Thus, wood is pre-stressed in tree.

In the case of compression wood, there is a tendency to longitudinal expansion cell caused by a swelling matrix associated with a high microfibril angle. But this phenomenom being prevented by the bioenvironnement rigidity and compression wood is under compressive longitudinal stress (easily estimable at experimental level by the measurement of two points displacement after maturation strains relaxation). Those LRSM measured in stem surface, when stem longitudinal continuity is interrupted (by making tapping, drilling... in xylem under cambium area), are usually linked with tree morphology and peculiar wood anatomy.

The used method for the determination of LRSM is the single drilled hole method (Mitutoyo sensor on CIRAD structure, Fig. 3). Studied trees (22 years old pinus -*Pinus pinaster* Ait-) are morphologically different and show typical strain peaks, those peaks are correlated with the phenomenom of stem orientation.

The basal sweep and the fork are schematized in figure 1 and 2 with the principal localisations of measurements and values given by the sensor.

BIBLIOGRAPHY.

Baillères H., 1994. Précontraintes de croissance et propriétés mécano-physiques de clones d'Eucalyptus (Pointe-Noire, Congo): hétérogénéité, corrélations et interprétations histologiques. *Thèse en Sciences du Bois de l'Université de Bordeaux I*, 161p.

Chanson B., 1993. déformation de maturation: hétérogéinétés angulaires en fonction du plan d'organisation des arbres. *Acta Botanica Gallica* 140(4), 395-401

Fournier M., Guitard D., 1993. Les contraintes de croissance générées par la différenciation cellulaire. *Acta Botanica Gallica* 140(4), 389-394

Timell T.E., 1986. *Compression Wood in Gymnosperms*. Springer-Verlag, 3 volumes,2150p.
<figure><img src="image_61.png" /><figcaption>Fig. 1: The basal sweep.
(Angular sectors in abscissa, values given by the sensor in ordinate)</figcaption></figure>

<figure><img src="image_62.png" /><figcaption>Fig. 2: The fork.</figcaption></figure>

<figure><img src="image_63.png" /><figcaption>Fig. 3: Single drilled hole method.</figcaption></figure>
EFFECT OF WIND ON SOME ALLOMETRIC RELATIONSHIPS
OF TWO PLANT SPECIES
OF AN ELFIN SUBTROPICAL FOREST

CORDERO Roberto A., VOLTZOW Janice and FETCHER Ned

Department of biology, University of Puerto Rico,
PoBox 23360 Rio Pedras, PR 00931

Exposure to wind typically produces a reduction in organ length in plants. For plants
growing in the cloud "elfin" forest, we hypothesized an increase in structures for
mechanical support at the expense of growth in height and length. This hypothesis was
tested in a transplant experiment in Pico del Este cloud forest, in the Luquillo
Experimental Forest, in Northern Puerto Rico. This forest is also subjected to
disturbances produced by high wind speeds. Plants of *Clibadium erosum* (a shrubby
Compositae) and saplings of *Prestoea montana* (a mountain tree palm, Arecaceae) were
grown from cuttings and seedlings, respectively, during almost three years. Barriers
were used to protect randomly selected individuals from the wind.

For *Clibadium*, we used regression to examine the relationship between basal diameter of branches and branch length, in order to compare the slope with the one predicted by the power law model. We found a significant effect of barrier on the slope of the relationship indicating that exposure to wind produced overbuilt structures. We also found an effect of the barrier on the slope of the relationship between basal diameter of branches and total area of leaves on the branch.

For *Prestoea*, we studied the effect of wind on the leaf allometric relationships by considering the petiol as a columnar structure supporting a laminar load. We used the same analysis performed with *Clibadium*. We also consider the leaf type. As seedlings, this species presents simple laminar structures as leaves. Later, plants developes pinnately compound leaves. We found that the slope of the relationship between petiol diameter and leaf lamina area was significantly different between leaf types. This relationship seems to be influenced by the wind treatment. Other parameters like leaf dimensions related to petiol relative sizes did not changes between leaf types.

These results indicate that wind could be an important factor influencing plant form in
cloud forest and may contribute to the dwarfed structure of the plants.

Actually, we are beginning to test some biomechanical properties of trees and shrubs
trunks by mean of field bending tests. Also, we are interested in obtain relationships
between growth patterns and field biomechanical properties for these trees, that help us
to understand the "elfin" structure of this forest association.
TITLE: The structural development of the stems and anchorage roots of winter wheat, *Triticum aestivum* L

M.J.Crook, A.R.Ennos & E.K.Sellers: School of Biological Sciences, University of Manchester, Williamson Building, Oxford Road, Manchester M13 9PL.

## SUMMARY

The structural development of the stems and basal anchorage roots of two winter wheat cultivars (*Triticum aestivum* L) were investigated and related to their mechanical function. Stem and root morphology, anatomy and mechanical properties were examined from tillering (March) up to maturity (August), together with plant weight distribution. This allowed us to calculate a "factor of safety" against root and stem failure throughout development.

As the plants grew taller the stem and the anchorage "coronal roots" increased in bending strength countering the increasing mechanical demands. The bending strength, in turn, was correlated with the amount of lignified material around the stem and root perimeter. Structural development ceased by ear emergence, when the plant was at its tallest, but because the ear weight continued to rise the "self-weight" moment pushing the plant over continued to increase. This meant that the "Safety Factors" of both cultivars against both root and stem mechanical failure decreased throughout development (Figure 1). In both cultivars the safety factors against root failure were lower than for stem failure, and Galahad had lower factors of safety than Hereward. All these findings were consistent with results of field trials; failure tends to occur late in development, during grain filling, and is localised to the root system, whilst Galahad is more prone to failure than Hereward.

The pattern of mechanical development of winter wheat seems to be one which would maximise its reproductive success, maintaining its structural integrity especially early in development while investing in a minimum of structural material.

Figure 1: "Safety Factors" against mechanical failure: stem breakage (closed symbols) and anchorage failure (open symbols). Bars represent ± SE of the mean for stem safety factors (n=10).
<figure><img src="image_64.png" /></figure>
FLUORESCENCE MICROSCOPIC STUDIES OF SECONDARY
WALL DEPOSITION PATTERNS IN TRACHEARY ELEMENT
(TE) DIFFERENTIATION IN ZINNIA ELEGANS LEAF
MESOPHYLL CELL SUSPENSION CULTURES

DAYATILAKE, G.A.* and RAJAGOPAL, R.**

* Dept. of Crop Science, Faculty of Agric., Univ. of Ruhuna, Mapalana, Kamburupitiya, Sri Lanka, corresponding author

** Dept. of Plant Biol., Royal Vet. & Agric. Univ., Thorvaldesnsveg 40, Frederiksberg C, DK 1871 Denmark

Tracheary element (TE) differentiation of isolated mesophyll cells of *Zinnia elegans* (L) CV Envy was studied in cell suspension cultures. Changes in the secondary cell wall band deposition sequence and patterns were observed using calcoflour white (CW) fluorescent brightener. Using this procedure, the initiation of secondary cell wall deposition was observed 10-12 hrs earlier than that of phase contrast light (PCL) microscopy. At 48 hrs, the primary walls of the expanded mesophyll cells, faintly stained with CW, were only visible. In contrast, clearly stained cell plates were detected in dividing cells. Initial stages of depostion of the cell wall material, in an annular pattern was observed at 52 hrs. TEs which had been differentiated following initial cell division or directly were recognized, with brightly stained annular/spiral wall bands, at 64 hrs of incubation. However, under phase contrast light (PCL), only the reticulate, scalariform and pitted as well as some irregular patterns were noted in the cell suspension. During the course of TE differentiation, transition of the patterns were observed indicating that there was a continuing cell wall deposition which resulted in the transformation of annular or spiral patterns into scalariform or pitted patterns. In partially plasmolyzed cells with sorbitol, it was noted that the cell wall thickenings followed the contour of the protoplast and were not associated with the primary cell wall at the beginning.

Key words: Tracheary elements, Differentiation, *Zinnia elegans*, Secondary wall depositions.
BOIS JUVENILE ET BOIS ADULTE : RECHERCHE DE DIFFERENCES
CARACTERISTIQUES A TRAVERS L'ETUDE DU BOIS DE TENSION
DU WAPA, *Eperua falcata* Aubl. (CAESALPINIACEAE)

Olivia DELAVault

LMGC, Université Montpellier II, place Eugène Bataillon, Case courrier 081

34095 MONTPELLIER Cédex 5

Sur de jeunes Wapas ou sur des Wapas adultes, la recherche de la signification anatomique des mesures de relaxation des contraintes dans l'arbre sur pied, nous a conduit vers une approche du bois tant au niveau pariétal qu'au niveau cellulaire.

Cette étude vise plus particulièrement à identifier les évolutions entre le bois normal et le bois de tension à l'état juvénile et adulte. Des photos de coupes transversales observées en microscopie électronique à balayage (MEB) d'après lesquelles nous avons mesuré l'épaisseur des parois secondaires (S) et celle des couches gélatineuses (G), ainsi que les diagrammes de type nuages de points (Fig. A, B, C) qui expriment en µm l'épaisseur de S en fonction de celle de G, constituent le support matériel de cette analyse comparative.

L'observation et la superposition de ces figures montrent que :

* d'une manière générale, l'épaisseur de la paroi S des fibres du bois normal est nettement supérieure à celle des fibres de bois de tension, et ceci dans tous les cas envisagés (bois d'un jeune plant, bois juvénile prélevé dans le duramen d'un arbre adulte, aubier d'arbres adultes).

* dans le bois normal, l'épaisseur de la paroi secondaire des fibres d'un arbre adulte ([1,8-3,4µm]) recouvre celle des fibres d'un jeune plant ([1,8-2,25µm], photo 1) ainsi que celle des fibres du bois juvénile ([2,1-3µm]).

* dans le bois de tension, il existe pour les parois secondaires, vers les valeurs inférieures, un décalage du diagramme obtenu pour l'individu jeune (épaisseur de S comprise entre 0,5 et 1,5 µm) par rapport aux 2 autres diagrammes (épaisseur de S comprise entre 0,9 et 1,9 µm), alors que l'étalement relatif des valeurs de l'épaisseur pariétale est sensiblement identique dans tous les cas de figure (environ 1 µm).

* l'épaisseur de la couche G du bois de tension d'un jeune arbre (photo 2) ou celle du bois juvénile prélevé dans le duramen d'un arbre adulte (photo 3), s'étend sur une plage de valeurs plus grande que celle couverte par l'épaisseur de la couche G dans le bois de tension situé en périphérie du tronc d'arbres adultes (photo 4). Il existe donc, dans le bois à l'état jeune, des fibres dont la couche G est très fine (de 1 à 1,6 µm) qui sont absentes dans le bois à l'état adulte.

Des fibres gélatineuses qui diffèrent par l'épaisseur de leur couche G et/ou par celle de leurs parois secondaires mettent en évidence des différences caractéristiques entre le bois juvénile et le bois adulte. Mais il reste à comprendre la signification mécanique de ces différents faciès de bois de tension dans les phases successives de croissance de l'arbre.
<figure><img src="image_65.png" /></figure>

A/ Bois jeune

G (µm)

<figure><img src="image_66.png" /></figure>

B/ Bois juvénile

G (µm)

<figure><img src="image_67.png" /></figure>

C/ Bois adulte

G (µm)

<figure><img src="image_68.png" /></figure>

2

<figure><img src="image_69.png" /></figure>

3

<figure><img src="image_70.png" /></figure>

4

<figure><img src="image_71.png" /></figure>

Légende :

S=paroi secondaire; G=couche gélatinse;

● = moyenne des mesures pour chaque photo;

...... = écart type sur S et sur G

**Figures A, B, et C** : Diagrammes représentant l'épaisseur de la paroi S en fonction de celle de la couche G (en µm) pour le jeune plant, le bois juvénile et le bois adulte.

**Photos 1 et 2** : Bois de l'individu jeune. 1) bois normal (l'épaisseur de la couche S est de 2 µm); 2) bois de tension (les épaisseurs de G et de S mesurées sur cette photo sont respectivement 1,28 et 1,2µm).

**Photo 3** : Bois de tension de la partie juvénile (duramen) d'un individu adulte (les épaisseurs de G et de S mesurées sur cette photo sont respectivement 3,31 et 1,30µm).

**Photo 4** : Fibres de bois de tension prélevées dans l'aubier d'un individu adulte (S=1,12µm et G=2,56µm).
The effect of the availability of external support on allocation patterns in herbaceous climbing plants.

Koen C. den Dubbelden and Bertjan Oosterbeek.

Department of Plant Ecology and Evolutionary Biology, Utrecht University, P.O. Box 80084, 3508 TB Utrecht, The Netherlands.

Climbing plants differ from non-climbing plants in their morphology, anatomy and physiology mainly as a result of differences in biomechanical constraints. Climbers utilize external structures as support. Although this enables them to use stem biomass for stem length rather than for rigidity (Darwin, 1876; den Dubbelden & Verburg, in press) it also makes them dependent on the availability of structures upon which to climb. Lacking the capacity to hold themselves upright, the growth of climbers will be restricted by their capacity to encounter suitable structures for climbing, and by their efficiency in ascending these structures (Putz & Holbrook, 1991).

In a greenhouse experiment we studied the effects of the availability of external support on the allocation of plant biomass to main stems and branches in herbaceous climbing plants from temperate zones. The experiment included three species of climbers from grasslands and verges that climb by means of tendrils, and three twining species from verges and forest-edges. Plants were germinated from seeds and grown for three months in pots containing a river sand medium that was regularly watered with a non-limiting nutrient supply. Simulating the success and failure of encountering and ascending external supporting structures, one third of all plants was supplied with support directly at the start of the experiment, one third was refrained from support during the whole experimental period and the remaining third was offered support halfway the experiment.

At the end of the experiment, all three treatments resulted in the same total amount of plant biomass for a given species. However, supported plants allocated relatively more aboveground biomass to their climbing main stem, while unsupported plants invested more plant mass in basal branches. The main stem of supported plants grew to be much taller than that of unsupported plants (Fig. 1.). The latter stopped growing after a few weeks, which was associated with the number of internodes formed. The number of basal branches was higher in unsupported than in supported individuals (Fig. 1). When the main stem of unsupported plants was supplied with support halfway the experiment, they were no longer able to climb, while the branches of these plants could climb into the support. Once the branches ascended the support, the branching frequency declined in comparison with plants that remained unsupported branching during the whole experimental period.
<figure><img src="image_72.png" /></figure>

Figure 1. Mean (±se) length of main stem (black bars) and mean (±se) number of branches (white bars) of a typical tendril climber *Vicia sepium* and a typical twiner *Convolvulus arvensis* as affected by support availability (S, supported, and U, unsupported during whole experiment; D, support was offered halfway the experimental period).

Our results show that the availability of external supporting structures, both in space and time, is an important resource that determines plant height and branching patterns in herbaceous climbing plants. A large number of branches, that can grow in any direction, enhances the possibility that external support is encountered. The number of branches seems to be determined by the ability of the main stem to locate support and in case of failure by the successful support attachment of branches.

## References

- Darwin, C. 1876. The Movements and Habits of Climbing Plants. - John Murray, London.

- den Dubbelden, K.C. & Verburg, R.W. Allocation patterns and growth rates in herbaceous climbing plants. - Oecologia (in press).

- Putz, F. E. & Holbrook, N. M. 1991. Biomechanical studies of vines. - In: The Biology of Vines (eds. F.E. Putz & H.A. Mooney). Cambridge University Press, Cambridge, pp. 73-97.
DYNAMIC MECHANICAL THERMAL ANALYSIS AND ITS APPLICATION TO
THE INVESTIGATION OF TEXTURAL DEFECTS OF LEGUMES

Andy J. DOWNIE, Dominique M.R. Georget, Andrew C. Smith and Keith W. Waldron.
BBSRC Institute of Food Research, Norwich Laboratory, Norwich Research Park, Colney,
Norwich NR4 7UA

The sensory texture of foods is the consumer's interpretation of the mechanical properties of that food. Any processing or storage of food, altering the chemistry of the commodity, may influence these properties and affect the demand for that commodity.
Legumes are an important source of dietary protein, especially in the developing countries.
However, this specific commodity is underutilised. A major reason for this is the tendency for certain seeds to develop textural defects; the main one being the storage-induced defect known as the hard-to-cook defect.

The defect results in a lack of cell separation upon cooking (Jones and Boulter, 1983). This behaviour has been widely attributed to an increase in the rigidity of the middle lamella of the cell wall as a result of pectin insolubilisation. The insolubilisation may itself be the consequence of pectin-cation binding in the middle lamella, or other forms of cross-linking.
In preliminary trials we are investigating the influence of water content and temperature upon the mechanical properties of the bean cotyledonary tissue. In the past a number of techniques have been used to characterise the mechanical properties of hard-to-cook beans, including the Mattson bean cooker (Mattson, 1946) and use of a puncture test (Bourne, 1972); trials with these apparatus are performed in parallel to those with the DMTA.

The present study uses broad beans as a model system for beans stored under tropical conditions, and employs the DMTA to assess the stiffness of cotyledonary sections at different initial water contents. Artificial conditions of high temperature and high humidity are employed to reproduce the tropical storage conditions. This procedure is employed as a general procedure has been shown to yield legumes which are hard-to-cook.
A comparative analysis is drawn between the results of the DMTA work and that of the other mechanical analyses.
Figures 1 and 2 show preliminary data on the effect of initial water content on the bending modulus- and tan δ-temperature scan.

REFERENCES

Bourne, M.C. (1972). Texture measurement of individual cooked dry beans by the puncture test. *J. Food Sci.*, **37**, 751

Jones. P.M.B., Boulter, D. (1983). The cause of reduced cooking rate in *Phaseolus vulgaris* following adverse storage conditions. *J. Food Sci.*, **48**, 623

Mattson, S (1946). The cookability of yellow peas: A colloid chemical and biochemical study. *Acta. Agric. Suec.* 2, 185
<figure><img src="image_73.png" /></figure>

<figure><img src="image_74.png" /></figure>

Figure 1 represents the data obtained when using beans of an initial water content of 7.69 %. Whilst figure 2 represents a higher initial water content of 20.66%.
# TURGOR IN THE GROWTH ZONE OF TALL FESCUE LEAVES AT LOW WATER AND NITROGEN AVAILABILITY: DRIVING OR DRIVEN FORCE ?

Jean-Louis Durand, Bertrand Onillon, François Gastal.

Station d'Ecophysiologie des Plantes Fourragères. INRA. F-86600 Lusignan, France.

## INTRODUCTION.

In grasses, leaf elongation is highly sensitive to nitrogen and water shortage. The leaf elongation rate (L) depends on the length (z) and the relative elongation rate (R) of the tissues situated in the growth zone. Turgor in the growth zone ($P_{zc}$) is the origin of the force inducing irreversible tissue elongation (Lokhart 1965):

$$R = L/z = \Phi (P_{zc} - Y) \quad (1)$$

where Y is the yield turgor and $\Phi$ is the extensibility. The aim of the work reported here was to determine the combined effects of nitrogen and water deficits on the length, the relative elongation rate and turgor of growing tissues.

## MATERIAL AND METHODS.

After two regrowth cycles from cutting at 5 cm, tall fescue plants (cv Clarine) were grown in growth cabinet. Half of the pots received a high nitrogen solution and the other half received a low nitrogen solution. Irrigation was stopped in half of the plants, the other receiving nutrient solution as before. L was determined by regression of daily measurements of leaf length on time. Water and osmotic potentials were determined at the end of the dark period on mature leaves (pressure chamber) and in the growth zone (psychrometry on sampled 5 mm long leaf segments). On a separate set of plants the length of the growth zone was measured using the pin hole technique described by Schnyder and Nelson (1988).

## RESULTS.

Nitrogen deficiency induced a large decrease of L at well watered conditions. With time after withholding water nitrogen deficient leaves elongated faster (Fig 1a). However the effect of drought, as measured by the leaf water potential of mature leaves, was the same under both nitrogen situations (Fig 1b). Both z and R declined during drought at high and low nitrogen (Fig. 2). Growth zone turgor ($P_{zc}$ = water potential - osmotic potential) in well watered plants was 0.5 MPa whatever the nitrogen level (Fig 3). Under drought, in the low nitrogen treatment, turgor increased continuously from 0.5 MPa to 1 MPa. In the high nitrogen treatment, $P_{zc}$ reached the same value after a transient decline.

## DISCUSSION.

The decline of z explained only one part of the effect of nitrogen deficiency on L. As $P_{zc}$ was unaffected by nitrogen nutrition under well watered conditions $\Phi$ or Y also were affected. Both z and R decreased due to water deficit and $P_{zc}$ declined only transiently in high N treatment. The stability of $P_{zc}$ during the first 5 days of water deficit indicates that $\Phi$ or Y had changed. This was also true for the local growth rate at 7.5 mm where
turgor was computed. For slow permanent alterations of L with constant P<sub>zc</sub> (for instance N effects) structural changes in the growing tissues such as cell size or wall thickness could explain the changes of Φ (or Y). Cell wall properties were more likely involved in the faster changes of L as during the first steps of a drying cycle at constant P<sub>zc</sub>. The constancy of P<sub>zc</sub> under contrasted circumstances suggests that it was regulated and that L variations were part of the regulation, which could be expressed by rearranging equation (1):

$$P_{zc} = L/(z \times \Phi) + Y \quad L>0 \quad (2)$$

P<sub>zc</sub> only increased when water deposition in the growing tissues was nil (L=0 and Φ=0) probably as a result of a continuing solute deposition associated to an interrupted water deposition in the growth zone.

<figure><img src="image_75.png" /></figure>

<figure><img src="image_76.png" /></figure>

<figure><img src="image_77.png" /></figure>

## LITTERATURE CITED

* Lokhart 1965. An analysis of irreversible plant cell elongation. J. Theor. Biol., 8, 264-275.

* Schnyder H, Nelson CJ. 1988. Diurnal growth of tall fescue leaf blades. I. Spatial distribution of growth, deposition of water, and assimilate import in the elongation zone. Plant Physiol., 86, 1070-76.
LE SAPIN ET L'EPICEA FRANÇAIS

PROPRIETES TECHNOLOGIQUES
&
IMPACT SUR LA SYLVICULTURE

A. EL OUADRANI
C. de LAFOND
J.D. LANVIN
F. ROUGER

Centre Technique du Bois et de l'Ameublement, CTBA
Département Structure
Unité Etudes et Recherche
10, avenue de St Mandé 75012 PARIS

L'importance des reboisements réalisés en France depuis une cinquantaine d'années situe la forêt française aujourd'hui parmi les plus productives d'Europe. Dans ce contexte, les essences résineuses en particulier, doivent trouver des débouchés valorisants, notamment en structure (charpente et ossature). Mais cette valorisation passe par une connaissance précise des caractéristiques technologiques, et notamment mécaniques. C'est pour pallier ce manque de connaissances que le CTBA a laqué en 1990 un vaste programme de qualification du sapin et de l'épicéa français.

Les objectifs sont multiples, puisqu'il s'agit à la fois :

- de conseiller utilement les politiques de boisement et les sylvicultures à développer.

- de renseigner les concepteurs d'ouvrage sur les performances du matériau.

- de proposer des systèmes "classement- résistance" garantissant la sécurité d'emploi des essences concernées, tout en assurant la valorisation optimale du potentiel forestier actuel et futur.

L'échantillonnage des placettes et des arbres est réalisé selon une méthode statistique intégrant les facteurs sylvicoles les plus pertinents : structure forestière (régulière ou irrégulière), classe de diamètre, classe de fertilité et altitude.

Au total, 1022 arbres ont été prélevés dans 206 placettes. Cet échantillonnage, validé par un groupe d'experts forestiers, est basé sur les données de l'Inventaire Forestier National et a été réalisé à l'aide des différents services forestiers régionaux (O.N.F, C.R.P.F, SERFOB).
Des pièces de dimensions commerciales sont débitées de façon à identifier précisément leur origine : région, placette (type de sylviculture et altitude), arbre (environnement dans la placette), billon (hauteur de prélèvement dans l'arbre), position de la pièce dans la section transversale de l'arbre.

Deux familles d'éprouvettes sont testées: éprouvettes de bois sans défaut de petites dimensions testées en flexion, traction longitudinale et perpendiculaire, compression axiale, cisaillement et fendage et éprouvettes en dimensions commerciales sollicitées en flexion et en traction longitudinale pour déterminer le module d'élasticité et la contrainte de rupture.

La largeur des cernes, la masse volumique et la nodosité locale sont mesurées avant de réaliser ces tests mécaniques. Au total plus de 4 300 pièces en grandeur d'emploi et 900 éprouvettes de bois sans défaut sont testés. La masse de données ainsi acquise fournit environ 43 000 informations d'ordre forestière et 23 000 données sur le matériau bois.

L'analyse des résultats d'essais conduit à énoncer les principales conclusions sylvicoles suivantes:

* La masse volumique de l'épicéa est plus sensible à une variation de largeur de cernes que celle du sapin.

A largeur de cerne égale, et au delà de 3 mm, la masse volumique du sapin devient plus forte que celle de l'épicéa.

Il n'est pas recommandé de favoriser une trop forte croissance de l'épicéa en veillant à la régularité et à l'intensité des éclaircies des plantations.

* La texture du sapin est environ 1,5 fois plus forte que celle de l'épicéa, et ceci quel que soit l'âge de formation du bois.

Quelle que soit l'essence, la texture augmente avec l'âge de végétation jusqu'à 80 ans puis elle a tendance à se stabiliser.

Cette caractéristique anatomique pourrait expliquer le comportement au séchage et à l'imprégnation de ces deux essences.

* Globalement, la rigidité et la résistance en flexion sont identiques pour les deux essences. Cependant l'épicéa est plus résistant mécaniquement quand il présente une largeur de cerne inférieure au millimètre.

Planter de l'épicéa à très faible altitude et hors de son aire naturelle conduit à produire du bois à très faible propriétés mécaniques.

Les propriétés physiques et mécaniques sont très différentes selon les régions d'approvisionnement.

La diversité de comportement mécanique relevé dans les différents massifs doit permettre d'orienter les politiques sylvicoles vers un choix judicieux d'une essence en fonction des caractéristiques stationnelles existantes et de l'utilisation finale des produits forestiers.
Champ de contraintes développé dans le sol
par la croissance des racines:
Considérations théoriques.

Auteur: A.G. Faure

Unité de Science du Sol
Domaine Saint-Paul
Institut National de la Recherche Agronomique
BP 91 - 84143 Montfavet Cédex

Résumé du poster.

La méthode des éléments finis est utilisée pour déterminer la distribution des contraintes développées dans le sol, au voisinage d'une racine, lors de sa croissance. L'étude porte sur l'influence de l'état physique du sol sur cette distribution en prenant en compte les modifications qu'il entraîne sur le développement morphologique de la racine. Ces lois sont fournies par lès expériences de N'Guyen sur le maïs placé en conditions contrôlées de croissance.

Lorsque la racine se développe, des zones de plasticité de forme quasi circulaire apparaissent autour de l'apex et la méthode des éléments finis permet d'en déterminer l'évolution en fonction du développement de la racine.

Ce modèle théorique permet de changer les paramètres des lois morphologiques lorsque la réaction du sol devient importante ou lorsque ses propriétés mécaniques évoluent. Il établit ainsi les possibilités de prendre en compte simultanément les diverses interactions mécaniques développées entre le sol et la racine.

Cette méthode paraît plus performante que les hypothèses basées sur l'expansion cylindrique ou circulaire du champ de contraintes autour de la racine.

Il devrait rendre possible une meilleure simulation de la croissance des racines que ne le fait l'analogie de l'action du pénétromètre.

Actuellement le modèle fonctionne sous les hypothèses de contraintes planes, avec un sol élasto plastique répondant au critère de Drucker-Prager.
<figure><img src="image_78.png" /></figure>

Maximum principal stress in the vicinity
of the root tip

element 693

element 720

element 721

<figure><img src="image_79.png" /></figure>

Rylon Sand A

Rylon Sand B
# Mechanical Properties of Plant Tissue, Isolated Cells and Isolated Cell Wall Material.

T.J.Foster, M.J.Gidley, B.J.Briscoe*, D.R.Williams*, A.J.Barraclough, and P.J.Lillford.

Unilever Research, Colworth Laboratory, Colworth House, Sharnbrook, Bedford, MK44 1LQ, UK.

*Dept. Chemical Engineering, Imperial College, Prince Consort Road, Kensington, London, SW7 2BY, UK.

## ABSTRACT

Aspects of the mechanical and material properties of plant tissue, cells and cell wall material have been studied. Cell wall material and individual cells have been isolated from the pericarp tissue of a processing variety of *Lycopersicon esculentum* in order to study the properties of the cell wall matrix and the turgor pressure of cells individually. Techniques used in such analyses are mechanical spectroscopy (at Colworth) and individual particle upsetting technology (at Imperial College).

Cell wall material was produced by homogenising tomato pericarp tissue. After washing, it had a rather gelatinous appearance. The mechanical spectra obtained from such material were similar to those of biopolymer networks with G' and G'' almost independent of frequency, and η* decreasing as frequency increased with a slope ~1.

*In vitro* enzyme hydrolysis of plant tissue has been difficult to study in the past because of uncontrollable enzyme diffusion. However, enzyme incubation with cell wall material provides direct access to substrates, and the hydrolysis of cell wall material by a variety of cell wall acting enzymes has been followed by mechanical spectroscopy.

Tomato cells are isolated by soaking pieces of pericarp in calcium chelating (50mM CDTA) solution. Most of the cells retained their viability and it proved possible to alter turgor pressures by soaking in a range of mannitol solutions. The mechanical properties of cells at varying stages of turgor may then be tested, both as concentrated dispersions (mechanical spectroscopy) and as isolated cells (force deformation behaviour).
# Simulation d'un arbre en croissance : relations architecture / mécanique.

Th. FOURCAUD¹, F. BLAISE², P. LAC¹

1. Laboratoire de Rhéologie du Bois de Bordeaux - UMR 123 CNRS, INRA, Univ. Bordeaux I Domaine de l'Hermitage BP 10 33610 Cestas Gazinet.

2. Unité de Modélisation des Plantes CIRAD BP 5035 34032 Montpellier CEDEX 01

## Modélisation et simulation de la croissance des arbres.

**Mise en place de l'architecture aérienne.** Une méthode originale de modélisation et de simulation de la croissance et de l'architecture des végétaux a été développée au CIRAD. Elle s'appuie sur les connaissances qualitatives apportées par l'école de Hallé [1] en architecture végétale et sur les méthodes quantitatives mises au point au CIRAD dans le cadre de l'AMAP [2] (fig.1). Ces méthodes sont basées sur la description du fonctionnement des bourgeons (croissance, mort, ramification) par des processus stochastiques. La simulation du modèle est assurée par le logiciel AMAPpara. Ce dernier permet d'établir l'architecture d'un arbre à un âge donné en faisant fonctionner parallèlement tous ses bourgeons selon leurs lois propres de croissance, de mort et de ramification. La gestion en parallèle des bourgeons actifs permet d'obtenir, à tout moment de la croissance, une topologie cohérente de l'arbre [3]. Le résultat de la simulation est une description géométrique en 3D de l'arbre qui est utilisée pour la visualisation, mais qui peut servir de base à d'autres applications tel le calcul des transferts radiatifs.

**Modèle de simulation de la grosseur des axes.** La cohérence topologique de l'arbre permet de connaître le nombre d'unités de croissances feuillées susceptibles de produire des assimilats par photosynthèse. La quantité d'assimilats déposée le long des axes dépend du mode de diffusion utilisé (uniforme, non uniforme avec dépôt binomial ...). La simulation de ces modèles de diffusion permet de calculer la largeur des cernes internes résultant de la migration des assimilats (fig.2) [4].

## Couplage architecture / biomécanique de l'arbre.

**Calcul des structures par pas.** L'utilisation d'un algorithme de simulation du parallélisme dans AMAPpara permet de déterminer l'évolution du comportement mécanique d'une plante à chaque étape de son élaboration. A cet effet, un module de calcul mécanique utilisant la Méthode des Eléments Finis est actuellement développé au Laboratoire de Rhéologie du Bois de Bordeaux. Cette méthode s'appuie sur l'écriture d'une formulation incrémentale d'équilibre originale adaptée aux structures de volume variable [5]. Deux types de chargement sont pris en compte à chaque pas de croissance :

- l'incrément de poids propre de la structure (croissances primaire et secondaire);

- les précontraintes induites par les déformations de maturation du bois dans les cernes périphériques [6], [7]. Un différentiel de ces déformations dans une section droite entraîne une flexion des axes permettant à l'arbre de se réorienter (tropismes, recherche de la lumière ...) (fig.3).

**Applications.** Ce module de calcul est totalement interactif avec le moteur de croissance AMAPpara. Il permet d'une part de calculer la géométrie des branches, d'autre part de déterminer l'évolution des contraintes mécaniques dans chaque cerne du tronc d'un arbre tout au long de sa croissance (fig.4), ceci en relation avec son architecture (répartition des
charges, largeur des cernes). Les applications de ce logiciel sont nombreuses et couvrent différents domaines de recherche. En particulier, il permet d'étudier l'influence des arcures des branches sur le mode de ramification chez certains arbres fruitiers (phénomènes d'épitonie). Il est aussi un outil pouvant permettre d'analyser la qualité du bois chez un arbre en peuplement (influence de la compétition sur le champ de contraintes dans la grume, influence de la présence de fourches etc. ...).

Références :

[1] Hallé F., Oldeman R.A.A. et Tomlinson P.B., 1978. *Tropical Trees and Forest*. Springer-Verlag, Berlin, Heidelberg, New-York, 44 p.

[2] Reffye (de) Ph., Blaise F. et Guedon Y., 1993. *Modélisation et simulation de l'architecture et de la croissance des plantes*. Revue du Palais de la Découverte, Vol.21, N°209, pp 22-48.

[3] Blaise F., 1991. *Simulation du parallélisme dans la croissance des plantes et application*. Nouvelle thèse N°1071, Université Louis Pasteur, Strasbourg, France.

[4] Reffye (de) Ph. et al., 1994. *Essai sur les relations entre l'architecture d'un arbre et la grosseur de ses axes végétatifs*. Publication INRA (à paraître).

[5] Fourcaud Th. et Lac P., 1993. *Modélisation mécanique de la croissance des végétaux*. Actes du Colloque National en Calcul des Structures, Giens, Var 11-14 mai 1993, Edition Hermès, Vol.1:131-140.

[6] Archer R.R., 1986, *Growth stresses and strains in trees*. Springer Verlag series in Wood Science, Edited by E. Timell, 240p.

[7] Fournier M., 1989. *Mécanique de l'arbre sur pied : maturation, poids propre, contraintes climatiques dans la tige standard*. Thèse de l'Institut National Polytechnique de Lorraine.

<figure><img src="image_80.png" /><figcaption>Figure 1 : Evolution des Unités de Croissance dans une architecture de type Merisier.</figcaption></figure>

<figure><img src="image_81.png" /><figcaption>Figure 3 : Déséquilibre et redressement d'un pin.</figcaption></figure>

<figure><img src="image_82.png" /><figcaption>Figure 2 : Largeurs des cernes du tronc pour une diffusion uniforme des assimilats.</figcaption></figure>

<figure><img src="image_83.png" /><figcaption>Figure 4 : Contraintes longitudinales dans une section droite du tronc.</figcaption></figure>
# The impact of the ramification on the architecture of Tilia during its development phases

Peter GLEIBNER

Institute of Botany, Dep. Plant Morphology, RWTH Aachen, Worringer Weg, D-52056 Aachen

The crown habit of the linden (*Tilia platyphyllos SCOP. und T. cordata MILL.*) is well characterized by two symptoms in winter state. Firstly the twigs in the peripheral layers of the crown are of planar construction as well as those of the orthotropic tree top. Secondly the persistent frame branches at the crown center are nearly orthotropic, the thickest ones forming monoaxial (in a straight line) stems. It is shown which morphological processes are responsible for branching and to what extent it is possible to understand the architecture of the whole tree by these insights. It is an essential part of the examination to take into account important changes in branching during different stages of crown development (the vegetative, adult and senescent phases). These alterations in tree structure are considered to be innate to the genetic model because they occur independent of environmental influences.

## 1. Branching in peripheral layers of the crown

During the vegetative phase the branching system arises from a succession of renewal axes each beginning on top of each other (sympodial shoot connection) resulting in a monoaxial twig or branch. Distal lateral shoots are smaller turning off at an angle of 80°. In accordance with this the extension mode of the lateral shoots is acrotonic. The planar construction of twigs is formed by the interaction of distichous leaf arrangement and a local torsion at the beginning of each lateral shoot. Its first leaves are transverse to its descendent axis, but only by turning 90° the branching plane of the preceding axis is adjusted again. Lamma shoots arising sympodially are of the same structure as the spring shoot.

During the adult age (from 15 to 25 years) planar branching arises from other morphological processes because two shoot generations differing in structure are produced in succession each year. The first one is vegetative being homologous to the shoot before adult stage. The second one is the inflorescence axis. The latter unfold syllepticly on the vegetative shoot each having again a basal innovation bud¹.

Branching in one plane comes about by the interaction of two processes: The flowering axis with frail extension is inserted obligately between two vegetative axes and it is placed transversely to them with regard to the two orthostichies. The innovation buds at the base of the inflorescence axes are, moreover, the winter buds of the tree and are not homologous to those of the vegetative phase. The top innovation bud is not excluded from this way of branching.

By the extension mode of lateral shoots - here acrotony - we can also predict which axes of the peripheral layers become frame branches and which are shed by abscission: The apical lateral axes descending in a straight line are persistent, the smaller proximal ones are shed from the 4th to the 10th (15th) year of their lives. The latter can be recognized by their wide angle of turning off.

## 2. The architecture of the linden and its metamorphoses

During its lifespan three different models of correlating the frame branches can be characterized. During the initial phase of the first ten years several nearly upright frame branches arise competing in building the crown - called the **polyaxial-orthotropic** model (Fig. A). The further crown enlargement is based on them resulting in monoaxial stems by the above mentioned shoot connection. Each of these dominating stems forms a **monoaxial-orthotropic** unit together with thinner frame branches which turn off in a oblique direction (Fig. B). Such a subsystem is striking within the crown as a whole and, moreover, in later adult stage it is visible in the retuse hem line of the crown.
In this way the linden gains its maximum spreading at the age of 120 - 130 years (Fig. c). Then senescence has already started at lower sections of the crown: Reiteration shoots arise from proventitious buds on the upper side of the plagiotropic frame branches after their apical parts go out of operation or have already been broken off. Finally the innovation also wanes in the peripheral layers of the crown. The original region of the tree top is obviously thinned by the tree itself. Larger sections of the framework break off leaving gaps which are no longer compensated by reiterations also arising here. Over the age of about 300 years the lime tree has only a half or a third of the original crown volume (Fig. D). Often only the trunk and the base of lower main branches remain. Then all other twigs and branches are produced by series of reiterations lined up plagiotropically with their distal segments. This is why the architecture of old age is called polyaxial-plagiotropic.

<figure><img src="image_84.png" /><figcaption>Fig. A-D: the habit of the lime during its developmental phases (details from the poster), B-D at the same degree, RS = reiteration, further explanation see text</figcaption></figure>
New aspects of pattern analysis of branching systems including
its variation by forest dieback shown in maple and birch

Peter GLEIBNER

Institute of Botany, Dep. Plant Morphology, RWTH Aachen, Worringer Weg, D-52056 Aachen

Apart from the viewpoint of modular tree construction an additional way of understanding the branch system of trees is suggested: They are built up of metameric units which lie on top of each other in a centrifugal direction. Basic characteristics of axis morphology are closely linked with each of the following axis increments:

- the rhythmic change in leaf morphogenesis (between foliar leaf and bud scale)

- the rhythm in the length of the internodes

- the shoot extension mode (the position of the most extended lateral shoots per unit)

- the fixed position of inflorescences

In accordance with HALLÉ et al. (1978) this is the unit of extension (U<sub>E</sub>). It is shown by way of maple (*Acer pseudoplatanus* L.) and birch (*Betula pendula* ROTH.) that growth habit, the framework as well as fine-twigged peripheral layers, and its changes during life time can be characterized by the metamorphosis of the U<sub>E</sub> in time and space (i.e. the change of interaction of related parameters).

The maple axis system (Fig. 1) is built up by a sympodial way of shoot connection (= succession of terminal axes and lateral innovation axes (renewals), the latter here are caused by terminal inflorescence). During the vegetative phase (Fig. 1a) the U<sub>E</sub> consists of a terminal bud and lateral subacrotonic shoots (i.e. the extension mode is almost distal). In the later adult stage (b1 and b2) a switch takes place from a U<sub>E</sub> state similar to the vegetative phase and a U<sub>E</sub> state with terminal flowering, acrotonic renewals and decreased length. During later stages of adolescence (c1 and c2) the U<sub>E</sub> becomes shorter and shorter. The program of lateral shoot extension is also reduced. At phase a the total of U<sub>E</sub>s produces a monoaxial tree consisting of the primary stem and orthotropic frame branches which compete. The growth habit quite suddenly becomes polyaxial during adult stage (b,c). The axis system consists of 2-4-year modules with decreasing length depending on the age of the tree.

The U<sub>E</sub> of the birch shows interaction of two different times of unfolding shoots. The sylleptic mode produces lateral shoots in the middle part of the U<sub>E</sub> (mesotonic), the cataleptic one produces distal shoots (acrotonic) and female inflorescences at base (Fig. 2 a, during early adult stage). Later on, the terminal bud will regularly convert to a male inflorescence followed by a sympodial renewal axis (Fig. 2 b). This is the maximum program of the U<sub>E</sub>, which will usually be shortened in non-orthotropic shoots. At plagiotropic orientation (c) the cataleptic parts are established (the sylleptic one is reduced). On overhanging shoots only the base section with female inflorescences is established. All other shoots except these flowers end in a male inflorescence. Although the birch belongs to the group with continuously growing shoots, its axis system is articulated in a regular way. This is because the lateral shoots are produced rhythmically by the acrotonic and mesotonic extension mode.

We suggest that different developmental aspects such as vegetative and reproductive phases and the sylleptic and cataleptic programs be integrated into the description of the tree construction as a whole. In this way it is easier to recognize the different internal programsinate to the genetic model of a tree species. After all, the 'Gestalt' of the tree is definitely varied by external environmental factors.
Non-pathological diseases vary the branching pattern in the peripheral layers of the crown: the shortening of the abscission time of twigs, the breakdown of lateral axis differentiation, the reduction of the length of U<sub>E</sub> and the lack of lamma shoots.

<figure><img src="image_85.png" /></figure>

<figure><img src="image_86.png" /></figure>

HALLÉ, F./OLDEMAN, R.A.A./TOMLINSON, P.B. 1978: Tropical trees and forests. An architectural analysis. Berlin
# Biomechanical response of reed bamboo along the length of the culm and across the culm wall thickness

R. GNANAHARAN

Kerala Forest Research Institute

Peechi 680 653

INDIA

Bamboos are the fastest growing plants. They are a unique group of grasses which can be used for a variety of purposes. Unlike a tree, bamboos do not acquire more girth as they grow. The new sprouts emerge with full diameter. New culms reach full height in 3 to 4 months.

Reed-like bamboos or reed bamboos (*Ochlandra spp*) generally have thin culm wall and long internodes. *O.travancorica* (Bedd.) Benth. ex Gamble is the most common and commercially important reed bamboo which occurs in the evergreen and semi-evergreen forests of southern India. Culms of *O.travancorica* are tender during the first year and they become mature in the second year. Even though the culms can reach 7 to 10 m in height, the usable length is only 3 to 4 m.

Eight mature culms were collected from the natural forests. Usable lengths with six internodes were cut and removed. The internode lengths were measured. One ring of about 20 mm length was removed from the middle of each internode of five culms. Culm diameter, culm wall thickness, moisture content and density were determined from these rings. The basal, middle and top portions of the remaining three culms were split into slats of 12 to 15 mm width. Slivers of about 0.7 mm thickness were obtained from these slats across the wall thickness. These slivers were dried to about 12% moisture content and they were tested for tensile strength along the grain.

As diameter decreases from base to top from 28.3 mm to 19.4 mm, wall thickness reduces from 5.9 mm to 2.5 mm (Table 1). Reduction in wall thickness is very steep. An interesting feature of this reed bamboo is that, even though the top portion is thinner, it is denser. This is because of the arrangement and frequency of vascular bundles. The top internode had a density (625 kg/m³) which is nearly 35% higher than the density of the basal internode (463 kg/m³). Also, it can be seen from Table 1 that moisture content of green culm decreases from base to top.
As can be seen in Figure 1, tensile stress increases along the length of the culm. This clearly shows that density and strength are positively correlated. As density increases, strength also increases along the culm length. Figure 2 shows the radial variation of tensile strength from the periphery to the inner wall across the wall thickness. Slivers from outer periphery, with higher density, have higher strengths compared to slivers from the inner wall.

The biomechanical response of reed bamboo varies from base to top of the culm as well as from outer periphery to inner wall. If reed bamboo is used in round form or in split form or in the form of slivers, the strength will vary accordingly. It is quite important to know this difference so that the right portion of the culm is used for the right purpose.

<table><caption>Table 1. Basic data on the culms of *Ochlandra travancorica*</caption><thead><tr><th rowspan="2">Property</th><th colspan="6">Internode</th></tr><tr><th>1</th><th>2</th><th>3</th><th>4</th><th>5</th><th>6</th></tr></thead><tbody><tr><td>Internode length (mm)</td><td>535.0</td><td>584.0</td><td>627.0</td><td>677.0</td><td>690.0</td><td>668.0</td></tr><tr><td>diameter (mm)</td><td>28.3</td><td>27.7</td><td>26.3</td><td>24.6</td><td>22.6</td><td>19.4</td></tr><tr><td>wall thickness (mm)</td><td>5.9</td><td>5.6</td><td>4.2</td><td>3.4</td><td>3.1</td><td>2.5</td></tr><tr><td>density (kg/m³)</td><td>463.0</td><td>487.0</td><td>528.0</td><td>546.0</td><td>587.0</td><td>625.0</td></tr><tr><td>moisturecontent (%)</td><td>115.9</td><td>118.4</td><td>92.1</td><td>76.7</td><td>75.6</td><td>35.0</td></tr></tbody></table>

<figure><img src="image_87.png" /><figcaption>Figure 1</figcaption></figure>

<figure><img src="image_88.png" /><figcaption>Figure 2</figcaption></figure>
# Coloration macroscopique du bois de tension chez le Peuplier

Valérie GRZESKOWIAK, François SASSUS

LMGC/bois, CP 081, Université Montpellier II, Place E. Bataillon, 34095 Montpellier cedex 5, France.

Le bois de tension est un bois aux caractéristiques mécaniques et anatomiques différentes du bois dit "normal". Ce bois ne se trouve que chez les angiospermes. Il est généralement formé dans un secteur angulaire d'une section transversale de tige et pendant certaines phases de croissance seulement. Il est alors le moteur, pendant la fin de sa différenciation, d'une réorientation active (mouvement de flexion) de la tige (Fournier et al. 1994, Chanson 1993). Dans de nombreuses espèces, le bois de tension se distingue par la présence de fibres gélatineuses. Ces fibres ont une couche interne "G" constituée en majorité de cellulose cristalline. Chez le Peuplier, la couche G remplace la paroi S3. Le bois de tension forme des bandes tangentielles situées essentiellement dans le bois initial.

La mise au point d'une coloration macroscopique permettant la mise en évidence du bois de tension a rarement fait l'objet d'études systématiques. L'idée est de tester des colorants de la cellulose connus pour la préparation des coupes microscopiques (Jensen, 1962).

Le but est de donner une image de la répartition du bois de tension sans faire de coupes anatomiques. Cette cartographie permet de retracer l'histoire des réorientations de l'axe, ainsi que les profils de contraintes internes dans le bois à l'âge de l'exploitation (en utilisant en plus un modèle mécanique du cumul de ces précontraintes et la donnée des déformations de maturation dans le bois de tension). Ces observations sont à la base des travaux menés au LMGC sur la biomécanique de l'arbre qui visent à étudier les relations entre la qualité du bois et l'histoire du développement morphologique de l'arbre. Les problèmes de qualité dûs à la formation de bois de tension (fentes d'abattage induites par les forts gradients de précontraintes, tuilage et voilement des sciages et placages pendant le séchage, liés aux hétérogénéités de retraits) sont tout particulièrement étudiés.

## Matériel :

- le colorant utilisé est le chloro-iodure de zinc (ou réactif de Herzberg). Sa réactivité est basée sur la composition chimique particulière de la couche G.

- matériel végétal : peuplier clone I 214

## Méthodes :

- prélèvement sur un billon de deux rondelles successives d'un centimètre d'épaisseur

- badigeonnage avec le réactif sur la face inférieure de la première rondelle (Photo 1)

- coupe et coloration microscopique (safranine - bleu astra) sur la face supérieur de la seconde rondelle pour validation (Photo 2)

## Résultat :

- Les zones de bois de tension sont colorées en mauve. Le chlorure de zinc attaque les liaisons hydrogène situées entre les chaînes de cellulose. L'iodé (qui est responsable de la coloration) pourra alors s'accumuler entre les chaînes. Le bois normal est coloré en jaune. La coloration est fugace (une dizaine de minutes) et peut être renouvelée plusieurs fois

- Les coupes microscopiques nous confirment que l'iodé a bien coloré les zones de bois de tension.

## Utilisation et perspectives :

- La méthode a été appliquée par F. Sassus (1994, cf Poster dans ce même volume).
- Cette coloration ne sera applicable à d'autres espèces que si elles possèdent des fibres G caractérisées. Les bois devront être clairs afin de faire ressortir le contrasté de couleur.

- Lors des essais de coloration, nous avons pu observer des nuances de teinte (rose au mauve). Peut-on attribuer ces différences de couleur à des variations de propriétés physiques (densité) ou chimiques ? Ces variations sont-elles corrélées aux variations de déformations de maturation ? Peut-on alors détecter différentes "intensités" de bois de tension ? Des études complémentaires sont en cours.

**Bibliographie :**

Chanson B., 1993 : Déformations de maturation : hétérogénéités angulaires en fonction du plan d'organisation des arbres. *Acta Bot. Gallica*, **140** (4), 395-401.

Fournier M., Chanson B., Thibaut B., Guitard D., 1994 : Mesure des déformations résiduelles de croissance à la surface des arbres. Observations sur différentes espèces. *Ann. Sci. For.* **51** (2)

Jensen W.A., 1962 : *Botanical histochemistry*. U. California Berkeley. W. Freeman & Co. San Francisco.

Sassus F., 1994 : Contraintes de croissance et morphologie chez un clone de Peuplier. *DEA en Sciences du Bois*. *ENGREF Nancy (France)*.

<figure><img src="image_89.png" /><figcaption>Photo 1: Coloration macroscopique
au chloro-iodure de zinc (bt = bois de tension)</figcaption></figure>

<figure><img src="image_90.png" /><figcaption>Photo 2: Coloration microscopique
Safranine-bleu Astra</figcaption></figure>
# Computerized Tomography-
A Non Destructive Method for Evaluating
the Mechanical Properties and Strength of Trees

Adolf Habermehl and Hans-Werner Ridder

Medical Physics in the Center of Radiology
Philipps-University, Bahnhofstr. 7, 35033 Marburg/Lahn, Germany

## INTRODUCTION

Computerized tomography is the only non-destructive method in arborology yielding detailed density pattern of the trunk. It allows the quantitative determination of the locally varying absorption coefficients for penetrating radiation within a thin layer of the trunk and gives in the tomogram an image of the layer showing not only rot, hollows and other defects and the thickness of the wall at every point of the circumference but also the distribution of water in the stem so providing data which may be used for calculating and evaluating the mechanical properties and strength and the stability of the tree.

## EQUIPMENT

Different portable systems have been developed and built for computerized tomography of trees. All are using radionuclides as sources of radiation.

The MCT-3 is based on the translations-rotation-method. A base ring and a bearing ring can be divided into two separate parts to be put around the tree to be examined. They carry the source and three radiation detectors. Stepping motors perform the translational and rotational movements. The system is controlled by micro-computer. It can examine trees with a diameter up to 72 cm and has adjustable legs to perform measurements up to 2 m of altitude.

The MCT-F has a similar mechanical construction, but is based on the fan-beam method and has 30 detectors. (Fig. 1) It has an inner diameter of 100 cm and a stronger source to measure larger trees.
<figure><img src="image_91.png" /><figcaption>Fig. 1: Diagram of the MCT-F</figcaption></figure>

<figure><img src="image_92.png" /><figcaption>Fig. 2: Tomogram of a chestnut</figcaption></figure>

APPLICATIONS

Trees in parks and besides streets have been investigated to get informa-
tions for evaluating strength, stability and preservation states. Location
and extent of wounds and interior butt rot of different tree species could
be determined as well as the thickness of the wall along the circumference
(Fig. 2). Tomograms of silver lime trees, for example, revealed the trunk
structure consisting of several smaller trunks, the state of welding, areas
of higher moisture content and frost damages. The extent of welding of
frost damages could be detected as well as interior roots within the hollow
stems of lime-trees.

In forestry sciences decay, checks, heartwood formation, moisture content and, in general, the locally varying density within the stem could be studied. The method was applied for the detection of butt rot and its spreading within the stem in horizontal and vertical direction, for determining sapwood areas in spruce stems in dependence of fertilization, and for evaluating development and treatment of tree wounds, and the damaging by resin tapping. In all cases the suitability of the method was revealed, especially due to its possibility of examining living trees unlimitedly, at any time periods and without damaging the tree.

LITERATURE

Habermehl, A. u. Ridder, H.-W. (1992/1993): I: Methodik der Computer-Tomographie zur zerstörungsfreien Untersuchung des Holzkörpers von stehenden Bäumen; II: Anwendungen: Forstbotanische Untersuchungen; III: Anwendungen: Untersuchungen an Allee- und Parkbäumen; Holz als Roh- und Werkstoff I: 50: 465-474; II: 51: 1-6; III: 51: 101-106; - Habermehl, A. and Ridder, H.-W. (1994) : Computerized Tomographic Investigations of Street and Park Trees. Arboricult. Journ. (to be published).
# Défilement du tronc chez le chêne sessile; Test de différents modèles et influence de l'architecture.

HATSCH Elvire; RITTIE Daniel; DHOTE Jean-François.

Laboratoire de Recherches en Sciences Forestières- Unité de Dynamique de Systèmes Forestiers- ENGREF, 14 rue Girardet 54042 Nancy Cedex. FRANCE.

Nous avons décrit la géométrie de l'aubier et des accroissements ligneux dans des tiges de chênes sessiles (*Quercus petraea* (Matt.) Liebl.), en fonction de la hauteur.

Ce travail a été effectué sur 18 arbres jeunes (stades gaulis et perchis), de morphologies différentes, et se poursuit sur 100 arbres arrivés à maturité, issus de futaie et de taillis sous futaie.

Nous avons testé la validité de deux modèles reliant la formation du houppier et le développement de la tige : la loi de Pressler (1865 cité par Larson 1963) et le "pipe-model" de Shinozaki *et al* (1964), utilisés sur des résineux. La loi de Pressler décrit l'accroissement en surface qui, à un niveau donné est proportionnel à la biomasse foliaire présente au dessus, donc reste constante sous la base de la couronne. Le "pipe-model" est utilisé pour expliquer la répartition de l'aubier le long de la tige: la surface d'aubier est proportionnelle à la surface foliaire située au dessus.

Cette étude montre que les lois testées ne permettent pas de décrire clairement la géométrie interne des tiges de chênes sessiles, qui apparaît plus complexe que chez les résineux.

Nous avons regardé ensuite la validité de deux modèles de défilement fondés sur une adaptation mécanique ("Optimal Stem Mechanical design") : optimisation vis à vis des risques de casse au vent (Metgzer, cité par Larson, 1963) ou optimisation de la hauteur maximale atteignable (MacMahon et Kronauer, 1976). Ces théories modélisent le tronc (net de branches) par une poutre à section circulaire variable. Le premier modèle suppose que les efforts de compression ou de tension longitudinales, subis de haut en bas par la tige sous l'effet d'une force perpendiculaire (vent horizontal), sont répartis uniformément dans le bois (constant stress design); sous l'hypothèse d'un bois homogène, le modèle prévoit que le diamètre au cube (d³) de la tige augmente linéairement de bas en haut. Le second modèle suppose que pour un volume de bois constant, le défilement (allométrique) maximise la hauteur critique au-delà de laquelle la poutre "flambe". Ceci permet à l'arbre d'atteindre une hauteur importante en limitant les risques d'effondrement. Sous l'hypothèse d'un bois homogène, ce modèle prévoit que d²/³ augmente linéairement de bas en haut.

Comme énoncé par les auteurs précédents, aucune des deux règles ne s'applique à la zone basale de l'arbre qui correspond à l'empattement, de même qu'à l'intérieur de la couronne. Sur nos chênes, les régressions donnent de meilleurs résultats pour le second modèle en d²/³ (r² toujours supérieur et répartition des résidus sans biais).

Enfin, nos résultats montrent que l'insertion des branches crée des irrégularités dans le défilement du tronc. La ramification influe sur la distribution des surfaces des cernes et de l'aubier mais cela dépend de l'état de vigueur des branches; toutes les branches ne participent pas à l'élaboration du tronc. Au-delà des modèles précédents, la compréhension de l'acquisition de la forme de la tige passe par l'étude de l'influence des critères architecturaux (position des branches, fourche), de l'âge et de la taille de la couronne.

## Références bibliographiques :

Larson P.R., 1963. Stem form development of forest trees. *For. Sci. Monogr.* 5: 1-42.

Mac Mahon T.A., Kronauer R.E., 1976. Tree structures: deducing the principle of mechanical design. *J. Theor. Biol.* 59: 443-466.

Shinozaki K., Yoda K., Hozumi K., Kira T., 1964. A quantitative analysis of plant form - The pipe model theory. I. Basic analysis. *Japanese Journal of Ecology.* 14 (3): 97-104.
<figure><img src="image_93.png" /><figcaption>Fig. 1 Largeur d'aubier et surface d'aubier correspondante en fonction de la hauteur : arbre dominant de 59 ans.</figcaption></figure>

Ht.BaseHo: hauteur de la base du houppier; Ht.BaseFe: hauteur de la base des feuilles.

<figure><img src="image_94.png" /><figcaption>Fig. 2: Evolution de la surface des cernes de 1988 à 1992: surfaces cumulées sur cinq ans et les largeurs des cernes: moyenne sur cinq ans, 1988-1992 en fonction de la hauteur : arbre dominant de 59 ans.</figcaption></figure>

Ht.BaseHo, Ht.BaseFe: hauteur de la base du houppier et du feuillage.

<figure><img src="image_95.png" /><figcaption>Fig. 3: Régression effectuée avec le rayon moyen mesuré sur des rondelles à différentes hauteur le long de la tige nette de branche, chez deux arbres de futaie. On utilise le rayon à la puissance 2/3 (r2/3).</figcaption></figure>
Tissue stresses, their origin and biomechanical significance

Z. Hejnowicz and A. Sievers

Botanisches Institut, Universität Bonn, Venusbergweg 22,
D-53115 Bonn, Germany

Tissue stresses, longitudinal and transverse, were determined for the hypocotyl of sunflower using Poisson's ratios and data from measurements of: (i) changes in the length and width of the epidermal tissue (DT) which occur upon peeling from the hypocotyl and the forces necessary to restretch the isolated tissue to its original length in situ; (ii) the external compressive force and (iii) the external osmotic pressure required to prevent the extension of isolated ground tissue (GT) immersed in water or mannitol solutions. These three independent measurements gave a simular magnitude of the longitudinal forces (tensile in the DT, compressive in the GT), being 0.37 N in the apical region. More than 80% of the tensile force is concentrated in the epidermis, resulting in longitudinal stresses which are > 3 times higher than that due directly to turgor pressure there. Transverse tissue stresses - circumferencial in the DT and radial in the GT - were calculated from the longitudinal forces, so the study provides a complete, three-dimensional picture of the tissue stresses in the hypocotyl (Fig. 1).

A simple model, based on (i) symplastic turgor-induced extensions of tissues which differ in moduli of elasticity, and (ii) static equilibrium, predicts the occurrence of longitudinal tissue stresses in stem-like organs. The model was applied to the hypocotyl of sunflower. Tissue composite moduli of elasticity in the longitudinal direction for uniaxial and multiaxial stresses in the DT and the GT of the hypocotyl, which are necessary to calculate the longitudinal forces involved in the tissue stresses in the hypocotyl have been determined. In the DT, the moduli are strongly dependent on applied uniaxial stress due to stress-hardening. Thanks to the tensile stress, the DT acts mechanically in an intact hypocotyl having a hardened modulus. The force obtained from the model fits well that measured. The model obeys the condition of the minimum of strain energy in the organ. It follows that the tissue stresses may arise in the turgor-derived mechanism described by the model without differential growth of the tissues, as hitherto assumed, though a differential growth may modify the tissue stresses. As to biomechanical significance the following aspects are considered. (i) The tissue stresses represent an analogue of prestresses in engeneering constructions. To study this point, the stresses in the sunflower hypocotyl were released by treatment with auxin to cause differential growth counteracting the tissue stresses. The stability of the hypocotyl was strongly reduced. (ii) The tissue stresses in a growing organ allow to exceed the yield threshold of the tissue which has the highest modulus of elasticity; a longitudinal tensile stress in addition to that imposed by turgor on
the DT in sunflower hypocotyl is necessary to exceed its yield threshold. (iii) A considerable elastic energy is accumulated in the organ with tissue stresses. In a vertically growing stem this energy is distributed symmetrically around the stem axis. In a gravireacting stem this symmetry is broken and a bending moment appears. We studied this aspect using stems of *Reynoutria*. In this plant, in normal vertical position, the epidermis and the collenchyma are in tension and the GT is under compression. The longitudinal forces are considerable: 0.24 N per 1 mm of circumference, or 5 N for the stem of 6 mm in diameter. In a horizontally positioned stem the first expression of gravistimulation is lowering of the tension in the lower side by a wall loosening process: The collenchyma creeps on this side and a bending moment appears, tending to bend the stem upward. On the lower side, the tensile force in the collenchyma decreases to 30 % of the original one after 1 h of gravistimulation. When a horizontally positioned stem is restrained by binding to stiff rods the elastic energy is partly released from the tissue stresses but remains accumulated in the restraints. When the restraints are removed the stem rapidly bends.

longitudinal tensile
stress in the epidermis:

$2.5 \cdot 10^6 \text{ N} \cdot \text{m}^{-2}$

(turgor pressure = 0.55 MPa)

longitudinal compressive
stress in the ground tissue:

$0.15 \cdot 10^6 \text{ N} \cdot \text{m}^{-2}$

(turgor pressure = 0.50 MPa)

circumferential tensile
stress in the epidermis:

$0.43 \cdot 10^6 \text{ N} \cdot \text{m}^{-2}$

transverse-radial compressive
stress in the ground tissue:

$0.06 \cdot 10^6 \text{ N} \cdot \text{m}^{-2}$

<figure><img src="image_96.png" /></figure>

<figure><img src="image_97.png" /><figcaption>Fig. 1 The forces involved in tissue stresses and stresses themselves in the apical region of the hypocotyl of *Helianthus annuus*</figcaption></figure>
# THE MECHANICAL PROPERTIES OF TRANSGENIC PLANTS WITH MODIFIED LIGNIN.

David G. Hepworth

University of Reading Centre for Biomimetics, TOB1, Earley Gate, The University, Reading, RG6 2AT, UK.

The presence of lignin in plant cells has massive commercial consequences for processes such as the manufacture of paper. Here lignin has to be removed using chemical extraction methods which are both commercially expensive and environmentally unfriendly. Therefore it would be an advantage to grow plants with modified lignin. The problem is, how much modification can be carried out without greatly reducing the mechanical rigidity of the stem.

Tobacco plants have been produced by Zeneca with an antisense CAD gene blocking the conversion of phenolic aldehydes to phenolic alcohol's. The alcohol's are normally polymerised into lignin. In the antisense plants lignin is still produced but with a higher aldehyde content. When wood is stained with Schiffs reagent, antisense wood shows up dark red while control wood stains light pink. The wood of the antisense plants is much less stiff in tension than the wood of control plants. The mean Young's modulus for control plants is 2.58 GPa (sd, 0.08). The mean Young's modulus for antisense plants is 1.49 GPa (sd, 0.07). These values are for wood equilibrated at 100% relative humidity at 20°C. Drying wood out reduces the difference in stiffness between control and antisense wood. Sorption isotherms for control and antisense plants showed that
antisense wood contains more water (15 % more), which is free water. Extracting lignin components from the wood revealed that the lignin matrix in antisense plants is less cross linked than in control plants i.e. more material can be extracted using milder treatments. The conclusion from these results is that the antisense wood has a lower tensile stiffness due to lower cross linking in the lignin matrix.

The properties of antisense wood can be simulated in control wood by treating the wood with sodium hydroxide solution for a short time. This reduces the stiffness and increases the free water content of the wood.

Using image analysis of tissue sections I have plotted the thicknesses of cell walls with distance from the stem centroid and with height from the base of the stem and calculated the second moments of area of the different tissues in the stem at different heights. The results show that under green house conditions the antisense plants do not have increased wood cell wall thickness or increased second moment of area of woody tissue within the stem. Consequently the stems of antisense plants have a lower bending stiffness than the stems of control plants. Experiments are currently under way to grow antisense plants under conditions simulating wind stress to see whether this will induce them to compensate for the reduced stiffness of the wood.

References.

Fry, S. C. 1986. Cross-linking of matrix polymers in the growing cell walls of angiosperms. Plant Physiol. 37:165-186.

Halpin, C., Knight, M. E., Grima-Pettenati, J. Goffner, D. Boudet, A. and Schuch, W. 1991. Purification and characterization of cinnamyl alcohol dehydrogenase from tobacco stems. Plant Physiol. 98: 12-16.

Iiyama, K., Lam, T. B-T. and Stone, B. A. 1994. Covalent cross-links in the cell wall. Plant Physiol. 104: 315-320.

Monties, B. 1989. Lignins. In: Methods in plant biochemistry vol. 1 (Eds. P.M.Dey and J.R.Harborne). 113-157. Academic press.
# Turgor/Mechanical Property Relations in Potato Tuber Parenchyma

S. Hiller

Silsoe Research Institute, West Park, Silsoe,
Bedford, MK45 4HS, England.

In many plant organs, especially those not reinforced with long fibres, the interaction of cell turgor pressure with cell walls is a major determinant of structural stiffness (1). Falk et al showed experimentally that tensile stiffness was linearly related to turgor pressure in potato parenchyma tissue (2), while Murase et al highlighted the strain-rate dependence of stiffness values measured in compression (3). More recent work by Lin and Pitt studied the mechanical behaviour of apple and potato parenchyma equilibrated in a range of mannitol solutions, examining tissue stiffness and failure modes as a function of cell turgor pressure and strain rate (4).

The experimental work reported below was a small-scale trial with the object of verifying some of the results of Lin and Pitt for potato, albeit of a different variety.

Experiments were carried out to determine the quasistatic mechanical behaviour of specimens of potato tuber parenchyma, cv 'Cara', after soaking in a range of buffered and unbuffered mannitol osmotica, from 0.0M in 0.1M steps to 0.8M. The soak time required for the tissue samples to reach weight/dimensional equilibrium in the various solutions was monitored. Consistency of solution concentration was checked using a sugar refractometer. Two replicates were equilibrated in each of the eight solution strengths, for buffered and unbuffered solutions.

After equilibration of all the samples, the first of each pair of replicates was compressed between flat platens at a constant deformation rate until tissue failure. The second sample of each pair was loaded and unloaded cyclically to successively higher nominal 10% strain increments until failure. Results were plotted in nominal and in true stress/strain formats. Mean turgor pressures for cells within tissue samples were inferred from a knowledge of weight/dimension change with solution molarity.

Compression test results clearly differentiated the samples soaked in 0.0M, 0.1M and 0.2M mannitol solutions, from those soaked in solutions of higher concentration. However, it was found that large differences in stress/strain behaviour occurred for relatively small changes in the inferred mean tissue turgor pressure. It is interesting to speculate on the possible causes of such behaviour.

## References

(1) Atkins, A.G. The Basic Principles of Mechanical Failure in Biologicàl Systems in Food Structure and Behaviour, chap. 8, publ. Academic Press Ltd.; 1987; (pp 149-176).

(2) Falk, S.; Hertz, C.H.; Virgin, H.I. On the relation between turgor pressure and tissue rigidity. 1. Experiments on resonance frequency and tissue rigidity. Physiologia Plantarum; 1958; 11 (pp 802-817).

(3) Murase, H.; Merva, G.E.; Segerlind, L.J. Variation of Young's modulus of potato as a function of water potential. Trans. ASAE; 1980; pp 794-800.

(4) Lin, T.-T.; Pitt, R.E. Rheology of apple and potato tissue as affected by cell turgor pressure. J. Texture Studies; 1986; 17 (pp 291-313).
<figure><img src="image_98.png" /><figcaption>Fig. 1 Compression behaviour of potato tuber tissue (cv 'Cara') after equilibration in a range of buffered mannitol solutions of differing concentration.</figcaption></figure>

<figure><img src="image_99.png" /><figcaption>Fig. 2 Detail of low-strain portion of above graph, showing clear differences in gradient of stress-strain curve between variously equilibrated samples, even at the start of deformation.</figcaption></figure>
THE MECHANISM OF LEAF MOVEMENT IN BEAN PHASEOLUS VULGARIS

M.S. Irving<fnref n="1" />, S. Ritter<fnref n="2" />, D. Koller<fnref n="2" /> and A.D. Tomos<fnref n="1" />.

The trifoliate leaves of bean (*Phaseolus vulgaris*) exhibit heliotropic responses which are mediated by changes in the volume and length of specialised motor cells in the cortex of the pulvinus. This can be readily studied in the laboratory using exposure to unilateral light <fnref n="1" />.

The turgor pressure, osmotic pressure and individual solute concentrations of the vacuoles of cortical cells were determined in upper and lower sides of the pulvinus of *Phaseolus* at different leaf elevations. Single-cell sampling and analysis techniques were used <fnref n="2" />,³,⁴.

<figure><img src="image_100.png" /><figcaption>**Figure 1:** Turgor pressure in upper and lower cortical cells of the pulvinus at different leaf elevations.</figcaption></figure>

Results indicate that light-activated changes in leaf elevation are associated with, and presumably caused by, alterations in cell turgor pressure in the cortical region of the pulvinus (Figs 1 and 2). As the leaf is elevated, turgor decreases on the upper side and increases on the lower side.

However, osmotic pressure and ion concentration (K⁺, Cl⁻, Mg<fnref n="2" />⁺ and Ca<fnref n="2" />⁺) did not show significant changes at different leaf elevations (Table 1). Clearly, changes in turgor pressure are not due to osmotic adjustment of the protoplast. We conclude therefore, that the light-activated turgor pressure changes are facilitated by apoplastic osmotic regulation. There is evidence that turgor regulation by the apoplast occurs in sugarbeet and wheat mesophyll ⁵, and in *Suaeda maritima* ⁶. This behaviour is in sharp contrast, however, to

<footnote n="1">¹: School of Biological Sciences - UCNW Bangor, Gwynedd LL57 2UW, Wales UK. Tel - (0248) 351151 Fax - (0248) 370731</footnote>

<footnote n="2">²: Institute of Life Sciences, The Hebrew University, Jerusalem 91904, Israel.</footnote>
the phototropic responses of mustard seedlings where differential expansion is due to changes in cell wall mechanical properties⁷.

<figure><img src="image_101.png" /><figcaption>Fig. 2: Turgor changes in a single upper cortical cell in response to changes in light direction.</figcaption></figure>

<table><caption>Table 1. Inorganic solutes and osmotic pressure in upper and lower cortical cells of the pulvinus (mean of 3 plants ± SD).</caption><thead><tr><th>Pulvinus surface</th><th>Leaf elevation (°)</th><th>K<sup>+</sup> (mM)</th><th>Cl<sup>-</sup> (mM)</th><th>Mg<sup>2+</sup> (mM)</th><th>Ca<sup>2+</sup> (mM)</th><th>Osmotic pressure (mOsmol)</th></tr></thead><tbody><tr><td>Upper</td><td>+35</td><td>71 ± 34</td><td>112 ± 82</td><td>139 ± 8</td><td>15 ± 2</td><td>391 ± 45</td></tr><tr><td>Lower</td><td>"</td><td>60 ± 20</td><td>116 ± 34</td><td>161 ± 13</td><td>18 ± 17</td><td>427 ± 33</td></tr><tr><td>Upper</td><td>-5</td><td>109 ± 36</td><td>74 ± 15</td><td>140 ± 34</td><td>14 ± 14</td><td>388 ± 19</td></tr><tr><td>Lower</td><td>"</td><td>83 ± 31</td><td>161 ± 38</td><td>161 ± 29</td><td>9 ± 10</td><td>436 ± 60</td></tr><tr><td>Upper</td><td>-50</td><td>115 ± 22</td><td>94 ± 15</td><td>97 ± 4</td><td>16 ± 9</td><td>373 ± 78</td></tr><tr><td>Lower</td><td>"</td><td>77 ± 51</td><td>173 ± 22</td><td>183 ± 60</td><td>5 ± 6</td><td>436 ± 100</td></tr></tbody></table>

1. D. Koller and S. Ritter, (1994). *Plant, Cell and Environ.* (in press).

2. M. Malone *et al.*, (1989). *Plant, Cell and Environ.*, **12**, 919-926.

3. A.D. Tomos *et al.*, (1994). *In: Plant Cell Biology- A practical approach*. N. Harris, K.J. Oparka (Eds.), JRL Press (in press).

4. W. Fricke *et al.*, (1994). *Planta* (in press).

5. A.D. Tomos *et al.*, (1992). *In: Carbon Partitioning*. C.J. Pollock, J.F. Farrar and A.J. Gordon (Eds.), *Bios*, pp 71-89

6. N.J.W. Clipson *et al.*, (1985). *Planta*, **165**, 392-396.

7. T.C.G. Rich and A.D. Tomos, (1988). *J. Exp. Bot.*, **39**, 291-299.
# ANALYSIS OF THE MECHANICAL RESPONSE OF CELLULAR TURGID PLANT TISSUE

G. Jeronimidis and J.H. Liu

Centre for Biomimetics, TOB 1, Earley Gate
University of Reading, Reading RG6 2AT, UK.

This paper present results on the analysis and modelling of the deformation mechanics of turgid, multicellular plant tissue. The effect of cell geometry, dimensions and internal pressure levels has been related to applied average external loads, resulting global deformations of the tissues and to the cell wall stresses which arise from the combination of internal pressure from turgidity and from applied external forces. The aim of this work is to develop a quantitative model for the prediction of cell wall fracture and tissue damage.

The cellular structure of soft plant tissue (parenchyma cells) has been modelled as a regular array of closed hexagonal cells. The cell geometry can be changed by changing the length of the sides and the angle between them, with cubic and regular hexagonal arrays as two limit cases. The distribution of cell wall material in the model is controlled by its partitioning between edges (struts) and faces (plates). The cells are filled with an incompressible liquid. External loads, tensile or compressive, are applied to two opposite edges (Figure 1) and the deformation of the various elements is calculated; in the model, elements whose orientation is not parallel with the load direction experience both bending and stretching whereas the elements parallel to the load direction are subjected only to stretching or compression. This analysis follows the work of other researchers in this field [1-5]

The results of the full analysis can be summarised in a number of equations which describe the global average stress-strain behaviour of the tissue, the change of internal pressure due to applied external loads or deformation, and the magnitude of the cell wall stress. The parameters needed for the analysis are the average cell dimensions, the cell wall thickness, the elastic properties of the cell wall and the initial turgor pressure in the undeformed tissue.

Figures 2, 3 and 4 show some of the results obtained together with a comparison of stress-strain behaviour between experimental results (potato tissue in compression) and analytical predictions (Fig.2). Finite Elements simulation techniques are also being developed to extend this work to irregular cell geometries and non-uniform cell size distributions.
[1] Pitt, R.E. (1982) Models for the rheology and statistical strength of uniformly stressed vegetative tissue. *Trans. ASAE*, 1776-1784.

[2] Gibson, L.J. and Ashby, M.F. (1988) *Cellular Solids-Structure and Properties*, Pergamon Press, Oxford.

[3] Jeronimidis, G. (1988) Structure and properties of liquid and solid foams. In *Food Strucure - its creation and evaluation*, Blanchard, J. M. V. and Mitchell, J. R. Eds., 59-74, Butterworths, London.

[4] Gao, Q., Pitt, R.E. and Ruina, A. (1990) A mechanics model of the compression of cells with finite initial contact area. *Biorheology*, 27, 225-240.

[5] Gao, Q. and Pitt, R.E. (1991) Mechanics of parenchyma tissue based on cell orientation and microstructure. *Trans. ASAE*, 34, 223-238.

<figure><img src="image_102.png" /><figcaption>FIGURE 1

Deformed Cell Geometry</figcaption></figure>

<figure><img src="image_103.png" /></figure>

<figure><img src="image_104.png" /></figure>

<figure><img src="image_105.png" /></figure>
MECHANICAL RESPONSE OF PLANT TISSUE TO IMPOSED
COMPRESSIVE DEFORMATIONS

G. Jeronimidis and B. M. Stühlen

Centre for Biomimetics, TOB 1, Earley Gate

University of Reading, Reading RG6 2AT, UK.

Experiments carried out on cylindrical specimens extracted from potato and sugar beet have shown that when these tissues are subjected to a constant, uniform applied compressive deformation, the applied load decreases initially, reaches a minimum and then increases again [1]. The plant tissues appear to be able to react actively to the imposed deformation, after some time. The increase in load at constant deformation implies a tendency to expand.

Typical load-time curves, at two different temperatures, for fresh potato tissue (Cara variety) are shown in Figure 1. The applied deformation corresponding to the initial load of 1.25 N is of the order of 0.4 %, well below the value where irreversible damage occurs. The tests have been carried out in an Instron testing machine with the tissue samples fully immersed in liquid paraffin to prevent water loss.

The initial reduction in force is associated with "passive" stress-relaxation behaviour of the polymeric materials in the cell walls. The rate of relaxation is strongly temperature-dependent, which corresponds to what is observed during the first few hours of testing. The increase in load which occurs after several hours is believed to be associated with some physiological response of the tissue, probably related to metabolic rates. The time of initiation of this "active" response, its rate and magnitude depend on test temperature, storage temperature before testing and, possibly, on light conditions. Figure 2 shows the difference in response between tissues stored before testing at 60°C and 240°C. The low temperature appears to inhibit the active response. This type of "active" response has been observed also in sugar beet and may well be very general for plant tissues with parenchyma cells under turgor pressure.

The effects of time, temperature, initial deformation levels, etc. will be presented in more detail, together with modelling aspects.

The mechanism associated with the type of observed response is not yet known. It is reasonable to speculate that one possible explanation is that the cells "sense" the applied load or deformation and react by changing the osmotic potential of the cell content, increasing turgidity as a response to the external stimulus [2-4]
References

[1] Purkayastha, S. and Peleg, M. (1986) Comparison between projected mechanical equilibrium conditions of selected food materials in stress-relaxation and creep. *J. Text. Studies, 17*, 433-444.

[2] De Baerdemacker, J. G. (1976) Determination of the viscoelastic properties of apple flesh. *Trans. ASAE*.

[3] Finney, E.E., Hall, C.W. and Mase, G.E. (1964) Theory of Linear Viscoelasticity applied to potato. *J. Agric. Eng. Res.* **9** (4), 307-312.

[4] Cosgrove, D.J. and Van Volkenburgh, E. (1984) Stress relaxation of cell walls and yield threshold of growth. *Planta*, **162**, 46-54.

<figure><img src="image_106.png" /><figcaption>Figure 1</figcaption></figure>

<figure><img src="image_107.png" /><figcaption>Figure 2</figcaption></figure>
IMAGING OF CELLULAR DEFORMATIONS FOR PLANT BIOMECHANICS

G. Jeronimidis and S.H.P. Tolkien

Centre for Biomimetics, TOB1, Earley Gate

Reading University, Reading RG6 2AT

The mechanical testing of plant structures requires accurate measurements of deformations. This is relatively straightforward in the case of average global strains of the tissues (leaves, roots, stems, branches, etc.) but becomes increasingly more difficult as the dimensions of the structural elements to be measured decreases. In many instances, for example, it is desirable to measure local deformations at the cellular level as well as global ones. Image Analysis combined with optical, electron or X-ray microscopy, provides a powerful technique for this kind of work. Image Analysis (IA) is principally used to acquire numerical data from photomicrographs or direct images of the sample. It can be employed to store and process, with relative speed and accuracy, a wide variety of tissue and cellular parameters such as counts, linear dimensions, volume fractions, shapes, orientation and local strain fields in deformed plant materials.

The poster will illustrate the use of Image Analysis applied to the direct measurement of cellular deformations within plant tissues subjected to tensile or compressive loading and to the identification of local micromechanisms of failure (cell wall rupture, cell wall buckling, etc.) associated with damage initiation. The primary information (image) has been obtained from a variety of sources: confocal microscopy, low-vacuum scanning electron microscopy and X-ray microscopy. This last technique, developed and refined at Unilever Research, Colworth, UK, consists in taking a "soft" X-ray picture of the tissue at various stages of deformation, exploiting optical principles to get sufficient magnification. The network of interconnected cell walls can be resolved with sufficient accuracy on a photograph to enable Image Analysis to process the information.

Examples of potato and sugar beet tissues before and after deformation will be presented, together with quantitative measurements of local strain fields at the cellular level, comparisons between global and local deformations and events related to damage initiation.
<figure><img src="image_108.png" /><figcaption>N-SEM micrographs of Potato tissue, variety Cara; 1-3 under tension, 2 under compression.</figcaption></figure>

Bradbury S (1979). *Microscopical Image Analysis: problems and approaches*.

*Journal of Microscopy*, **115**(2), 137-150.

Dziezac J D (1988). *Microscopy and Image Analysis for R&D*. *Food Technology*, 110-124.

Ford TW, S.A., Cotton RA (1991). *Soft X-ray contact microscopy of biological materials*. *Electron Microscopy Review*, **4**, 269-292.

Gunasekaran S, P.M., Shove GC (1985). *Optical Methods for Nondestructive quality evaluation of Agricultural and Biological materials*. *Journal of Agricultural and Engineering Research*, **32**, 209-241.
# GROWTH RESPONSES TO MECHANICAL STIMULATION IN SOME HERBACEOUS PLANTS

J.L. Julien, N. Boyer, M.O. Desbiez and J.C. Mauget*

Unité Associée Bioclimatologie-PIAF (INRA-Université Blaise Pascal), 4 rue Ledru, F-63038 Clermont-Ferrand Cedex 01.

* Unité Associée Bioclimatologie-PIAF (INRA-Université Blaise Pascal), INRA, Centre de Clermont-Fd-Theix, Domaine de Crouelle, F-63039 Clermont-Ferrand Cedex 02.

Different mechanical stimulations such as pricking, rubbing or bending induce growth responses in herbaceous plants consisting in a reduction of elongation and an increase in radial expansion (Boyer *et al.*, 1979; Desbiez *et al.*, 1981, Jaffe 1998)<fnref n="1" />.

These modifications are considered as a possible mechanism for improved protection against further mechanical perturbation in artificial or natural conditions.

The mechanisms leading to the growth responses have been widely described in *Bidens pilosa* and in *Bryonia dioica* and are now being studied in *Lycopersicon esculentum*.

The main following results have been obtained :

- In *B. pilosa*, cotyledonary pricks induced a growth inhibition in reference to the length of the cells (Table 1). No modification of growth in reference to the width of the cells were observed 24 hours after the mechanical stimulation. After cotyledonary pricks, the mitotic percentage was reduced by 72% compared to the control plants (Pichon *et al.*, 1993)<fnref n="2" />.

- In *B. dioica*, the lignin content of both untreated and rubbed internodes increased steadily during the 96 h following rubbing but was always higher in the rubbed ones (Figure 1). Twenty four and 48 h after rubbing, the number of lignifying xylem vessels was markedly increased (Figure 2). Phenylalanine-ammonia-lyase activity of rubbed internodes was already higher than in control plants 6 h after the mechanical stimulation and increased up to a peak at 48 h (Figure 3).

- The inhibition of the hypocotyl elongation has also been found in young plantlets of tomato in response to cotyledonary pricks. On another hand, in older plants, a rubbing treatment applied to the petiole of the second leaf induced an inhibition of the elongation of the above internodes and an increase in their diameter (Figure 4).

These data indicate that herbaceous plants respond to mechanical stimulations by reducing their elongation and increasing their radial expansion. These modifications are related to cell wall rigidification as a result of accelerated lignification. Nevertheless, several questions are raised :

- Is it possible to characterize the mechanical stimulation in physical term?

- Is there a proportional relationship between the growth response and the intensity of the mechanical stimulation?

- Do the observed modifications really lead to an increased mechanical resistance of the stimulated plants?

<footnote n="1">¹Boyer N., Gaspar T. and Lamond M. (1979). Modifications des isoperoxydases et de l'allongement des entre-noeuds de Bryone à la suite d'irritations mécaniques. *Z Pflanzenphysiol.*, 93, 459-470.</footnote>

<footnote>Desbiez M.O., Boyer N. and Gaspar T. (1981). Hypocotyl growth and peroxidase of Bidens pilosus L. Effects of cotyledonary prickings and lithium pretreatment. *Plant Physiol.*, 68, 41-43.</footnote>

<footnote>Jaffe M.J. (1988). Wind and other mechanical effects in the development and behaviour of plants, with special emphasis on the role of hormone. *Encycl. Plant Physiol.*, 11, 444-483.</footnote>

<footnote n="2">²Pichon O., Bonnin B., Gendraud M. and Desbiez M.O. (1993). Ionic and cellular responses to traumatisms in Bidens pilosa : Effect of light quality. *Plant Physiol. Biochem.*, 31, 175-180.</footnote>
<table><caption>**Table 1.** Variations of hypocotyl cell size and mitotic activity after cotyledonary pricks. Δ, percentage of variation between control and pricked plants [(control-pricked/control) x 100]. Measurements were performed at a distance of 0.2 mm under the cotyledonary node (for mitotic percentage) and at 2 mm under the cotyledonary node (for cell size). Values ± SE.</caption><thead><tr><th></th><th>Mitotic percentage</th><th>Length of cells (μm)</th><th>Width of cells (μm)</th></tr></thead><tbody><tr><td>Control plants</td><td>1.8 ± 0.7</td><td>148 ± 5.1</td><td>18.4 ± 0.2</td></tr><tr><td>Pricked plants</td><td>0.5 ± 0.1</td><td>98 ± 2.5</td><td>18.4 ± 0.6</td></tr><tr><td>Δ (%)</td><td>-72.2</td><td>-33.8</td><td>0</td></tr></tbody></table>

<figure><img src="image_109.png" /><figcaption>**Figure 1.** Lignin content of control and rubbed *Bryonia dioica* internodes at different times after treatment.</figcaption></figure>

<figure><img src="image_110.png" /><figcaption>**Figure 3.** Time course of PAL activity in control and rubbed *Bryonia dioica* internodes.</figcaption></figure>

<figure><img src="image_111.png" /><figcaption>**Figure 2.** Number of lignifying vessels per vascular bundle in control and rubbed *Bryonia dioica* internodes 24 h and 48 h after rubbing.</figcaption></figure>

<figure><img src="image_112.png" /><figcaption>**Figure 4.** Effects of rubbing the petiole of the second leaf of a tomato plant. A. Internode length in control □ and treated plants ■. B. Internode diameter in control □ and treated plants ■.</figcaption></figure>
# EVALUATING TRANVERSE STRAINS IN GREEN WOOD.

Delphine JULLLIEN,

Laboratoire de Mécanique et génie Civil, URA 1214 du CNRS

Université Montpellier 2, F 34095 MONTPELLIER CEDEX 5

During tree growth, wood appears by successive layers around the trunk (secondary growth). This formation mode leads to stress field introduction, consisting in longitudinal and transverse stresses. The longitudinal stress role is well known (tree bearing and orientation) and strain evaluating methods (Fournier) exist. Concerning transverse stresses, things are less mastered: they are revealed by heart checks, especially during steaming. We can note a peripherical tangential compression, which protects the tree in the sense that it contributes to close and heal cracks, but also contributes to brittle heart phenomenon. But there is still no simple way to evaluate the corresponding strains. This paper suggests one.

The study started because of the industrial problems caused by the heart checks apparition and their developpement during steaming. For this reason, the method is also applied to measure strains due to steaming operation.

## Material and method.

The studied samples are 8 or 16 mm thick wood disks, sawn from green trunks. Longitudinal release measurements have been made previously on the standing chesnut trees. The cutting operation consists in sawing off a thin angular sector from the periphery to the heart, and the steaming operation in heating the disk in 80°C temperature water in a bain-marie during half an hour.

The length-measuring device was made of a system of pins hammered in the disk and a modified displacement transducer measuring the distance between the pins. It allows to evaluate the lips end relative displacement due to cutting and steaming (fig.1). In some cases, numerous judiciously chosen displacements were also evaluated (fig.2), they verified measurement coherence.

## Results and discussion.

It appears that the lips end displacement divided by the remaining circonferency (fig.1) gives a good transverse strain estimate, obtained by a quick and simple way.

The graph (fig.3) shows only weak correlation between transverse and longitudinal strains. This result is not surprising because longitudinal strains reflect only the peripherical stress field, unlike the transverse ones that give a global value of the stress field integrating all the tree history locked in the whole section.

To gain better understanding of the experimental method, a numerical simulation using a finite element method (fig.4) was performed. First an initial residual stress field corresponding to the tree state prior to felling is simulated, through the successive addition of the stress field due to the deposition and maturation of new layers. Second, the cutting operation described above is simulated too.

## Conclusion.

To establish a better parallel between experimentations and simulations, tree growth eccentricity as well as wood material anisotropy will be taken into account.

Steaming is also an interesting aspect to develop since it allows to reach locked strains. Because steaming softens lignin and gives it back the rheological properties it had at the beginning of the lignification during wood formation, we can imagine that phenomenons observed at high temperature may be linked to wood formation in some way.
<figure><img src="image_113.png" /><figcaption>fig. 1: method of global transverse strain evaluation</figcaption></figure>

<figure><img src="image_114.png" /><figcaption>fig. 3: longitudinal-transverse
strains relation</figcaption></figure>

<figure><img src="image_115.png" /><figcaption>fig. 4: Finite element simulation of maturation-induced strains</figcaption></figure>
# Biomimicking of Plant Stems

G.N. Karam and L.J. Gibson

Department of Civil and Environmental Engineering
Massachusetts Institute of Technology
Cambridge, MA 02139

USA

## Abstract

Plant stems resist both axial load (due to their own weight) and bending moments (due to the wind). Failure is typically by local buckling of the compressive face. Microscopic investigation reveals that many plant stems are made up of an almost solid cylindrical shell lined with an inner layer of foam-like parenchyma cells (a "core-rind" structure). This foam core may totally or partially fill the shell.

Recently, we have analyzed the elastic buckling of a cylindrical shell with a compliant core under both uniaxial load and bending moment. The analysis showed that the foam core stabilizes the shell against local compression buckling due to axial load or bending moment. It also serves to prevent Brazier ovalization of the section under bending. The stresses due to shell buckling were found to decay to negligible values at a core depth equal to a multiple of the buckling wavelength. Removal of the core material beyond that given depth does not affect the buckling stress of the shell. The results of a parametric study indicates that for a given mass and diameter, a cylindrical shell with a foam core of sufficient depth for stress decay has a higher buckling load or moment than an equivalent hollow shell (Fig 1). The analysis has been confirmed by tests on silicone rubber shells with and without foam cores.

The microstructure of a number of plant stem cross sections was investigated. The shell radius, thickness and density and the core depth and density were measured. The parenchymatous core was modeled as an isotropic foam neglecting turgor pressure. The application of the results of the previous analysis to plant stems revealed their "core-rind" structure to be well described by the theoretical predictions based on the minimum depth for stress decay. The analysis also suggests that due to their microstructure, the plant stems can eliminate totally Brazier ovalization and can achieve improvements in their mechanical efficiency of a factor of up to 2 in local buckling resistance. The mechanical efficiency of other natural materials with a similar structure, such as porcupine quills and hedgehog spines, is also described. The effect of neglecting turgor pressure on the mechanical efficiency of plant stems is explained and the relationship
between mechanical and physiological function is investigated to explain differences in
mechanical efficiency among different natural strucutres.

The role of these simple mechanical efficiency models in understanding plant and
animal evolution and their potential application to the selection of agricultural varieties
with improved resistance to lodging is discussed.

Finally, we conclude by suggesting that the mechanical efficiency of engineering
cylindrical shell structures (eg. aircraft fuselages, offshore oil platforms) may be
improved by biomimicking the core-rind structure of plant stems.

<figure><img src="image_116.png" /><figcaption>Fig. 1 The ratio of (a) the uniaxial compressive buckling load and (b) the local buckling bending moment of a cylindrical shell with a foam core to that of an equivalent shell (of equal radius and mass) without a foam core. The foam core improves performance in uniaxial compression at higher core densities and shell radius to thickness values. The core improves the local buckling resistance in bending at all core densities and a/t values.</figcaption></figure>
BENDING PATTERN OF GRASSES WITH DIFFERING CONSTRUCTION

A.B. Kesel, W. Nachtigall, A. Wisser

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

Grasses (Poaceae) as slim self-supporting constructions are frequently exposed to the pressures of strong winds. These induced a load which is composed of statical as well as dynamical parts. The latter will be compensated by turn aside, which reduces the bending moments in the blade and enables it to tolerate high wind loads (Rasdorsky 1937, Vogel 1981). Nevertheless the statical wind load induces a high flexion which must be compensated by the arrangement and distribution of building materials (parenchyma, sclerenchyma) as well as stiffening structures (nodes).

Using a laminar wind tunnel, the bending patterns under continual loading of three species of grass (Lolium perenne, Molinia coerulea, Echinochloa crus-galli) are compared. Morphological and histo-morphological studies (cross-section analysis) allows the division into distinct types of construction. By observing the nodes, first morphological studies show two principle types: A) The nodes are distributed evenly throughout the stem (Lolium p., Echinochloa c.). B) The nodes are concentrated at the base of the blade, the stem is represented by the last internodes (Molinia c.).

The histo-morphological analysis show a peripheral arrangement of the sclerenchyma, which improves the flexural stiffness of the blade (Speck 1991, Speck and Vogellehner 1992). The arrangement of supporting elements (parenchyma, sclerenchyma) in the blade cross-section depends on the grass species and enables one to divide grasses into three main patterns of arrangement (Nachtigall et al. 1988) (Fig). In addition the observations show a species dependend distribution of the percentage parts of sclerenchyma and parenchyma, this distribution is changing along the blade length (decreasing: Lolium p. and Molinia c.; increasing: Echinochloa c.) (Tab).

<figure><img src="image_117.png" /><figcaption>Fig: A) Type I: Outer sclerenchyma ring (Lolium p.); B) Type II: Inner sclerenchyma ring with sclerenchyma rods leading to the epidermis (Molinia c.); C) Type III: Outer sclerenchyma ring and thinner inner ring (Echinochloa c.) (shadowed: parenchyma; black: sclerenchyma).</figcaption></figure>
<table><caption>Tab: Percentage parts of the stabilization materials in the three species of grass and the length dependend changing of the sclerenchyma part.</caption><thead><tr><th>species</th><th>Lolium p.</th><th>Molinia c.</th><th>Echinochloa c.</th></tr></thead><tbody><tr><td>lenght [m]</td><td>0,55</td><td>0,61</td><td>0,95</td></tr><tr><td>blade lenght [m]</td><td>0,39</td><td>0,48</td><td>0,82</td></tr><tr><td>parechnchyma [%]</td><td>63,5</td><td>57,5</td><td>85,3</td></tr><tr><td>sklerenchyma [%]</td><td>34,5</td><td>42,5</td><td>14,7</td></tr><tr><td>sclerenchyma changes [%]</td><td>-37</td><td>-8</td><td>30</td></tr></tbody></table>

In order to quantify the contribution of individual structure stabilizing elements, models of grasses under continual loading were made using the Finite Element Methode (ANSYS). The important arrangement of nodes (Gappoev 1991) and, in first calculations, the material distribution in the stem were also taken into consideration. The FE-Models aims to understand the contribution of the individual elements to stability as well as their combined influence.

From the arrangement of the structural elements together with surface interia moments and elasticity modules, one understands the bending resistance and thus the bending behaviour of the different grass constructions.

## References:

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

* Nachtigall W., Wisser C.M., Wisser A. 1988. Natürliche Konstruktionen - Mitteilungen des SFB 230, Teil I.

* Rasdorsky W. 1937. Über die Baumechanik der Pflanzen. Biologia generalis, Internationales Archiv für die allgemeinen Fragen zur Lebensforschung XII: 359 - 398.

* Speck T. 1991. Biophysikalische Methoden in der Paläobotanik: Möglichkeiten - Problematik. Ber.Naturf.Gesa. Freiburg i. Br. 79: 99 - 131.

* Speck T., Vogellehner D. 1992. Fossile Bäume, Spreizklimmer und Lianen. Versuch einer biomechanischen Analyse der Stammstruktur. Cour. Forsch.-Inst. Senkenber. 147: 31 - 53.

* Vogel S. 1981. Life in moving fluid. Boston.
# FRACTURE PROPERTIES OF AN ANISOTROPIC BIOLOGICAL CELLULAR MATERIAL - APPLE FLESH

## Abstract

Ali A Khan

Centre for Biomimetics, University of Reading, Reading, Berkshire, U.K.

The texture of apple flesh is important in assessing its eating qualities. The texture is in turn related to the structure of the parenchyma. The parenchyma cells of the fruit are predominantly arranged in radial quasi-columnar form with long radially arranged spaces in between. This anisotropy has a marked effect in the fracture properties such that it is much easier to drive the crack between the cell columns (radially) than to drive it across them (tangentially). The fracture tests used were simple crack-opening tests on geometrically cut specimens, e.g. notched tensile and wedge penetration tests. The latter is particularly useful for specimens which are small and awkwardly shaped and cannot be easily prepared for tensile testing. This directional difference in the mechanical properties was also detected by a taste panel. The radial spaces ease the passage of cracks travelling along them, and act as crack stoppers for cracks travelling at right angles to them. The spaces along with the radially elongated cells also allow the tissue to deform much more in the tangential orientation giving the structure greater ductility and making the parenchyma tougher in that orientation. It is possible to increase this effect by controlled damage to the material such as slow freezing which causes the intercellular spaces to expand increasing the crack stopping mechanisms and increasing the ductility, therefore increasing the fracture toughness. Toughness first increases, then decreases with increasing damage. This effect can be mimicked with brittle paper: fracture toughness of tracing paper initially increases if holes are punched randomly in it.
Biruta KRESLING
Bionics & Experimental Design
170, rue Saint-Charles
F-75015 PARIS France
Tel. (1) 40 60 96 06
Fax. (1) 45 58 38 75

Biruta KRESLING

Plant "Design" : Mechanical Simulations of Growth Patterns and Bionics (*)

A plant, capable of reacting to its real physical environment (i.e. to the internal and external forces acting on its structures), adapts its forms during growth, continually achieving a quasi-stable state. The resulting patterns reveal a complex process of feedback between growth and form.

These growth patterns may be mechanically simulated, and some of their principles transfered to industrial design.

The design of leaf venation may be interpreted as patterns made by processes of folding and unfolding, and the regular design of stems as patterns mady by buckling, i.e. by failure of cylinders or prisms under excessive axial load. Such interpretations help to compare the mechanical behavior of natural and of technical structures and offer some surprising and even paradoxical aspects.

With students in Experimental Design (**) kinetic structures were elaborated that may simulate either leaf development or growth patterns on cylindrical elements in plants (trees, grasses, cacti, wood tracheids). These kinetic structures are based on the engineering principles of astronautical "solar sails", which are foldable (K. MIURA), and of "plate-structures", which are stable (T. WESTER). Both may be made with thin walls or with low cost materials.

In order to create a convincing simulation it is essential that a natural structure be regarded not as one that attains a technically ideal state, but on the contrary, one of "constant failure" (buckling, bistability, deformation under stress). Real, dramatical failure during budding or under excessive mechanical constraints also reveal principles of design in plants.

For a better understanding of the particular "logic" of plant design, some bionic industrial products (i.e. based on mechanical principles of natural structures) are presented, such as: sandwich panels, composite materials, foldable, flexible or stiff/stable tubular structures (R. LE RICOLAIS, G. JERONIMIDIS and J.E. GORDON, B. KRESLING and students in industrial design).

<footnote>(*) Presentation supported by the MUSEUM NATIONAL D'HISTOIRE NATURELLE, Paris (Association pour la Promotion de la Binsonique)</footnote>

<footnote>(**) Valenciennes (ISD and SUPINFOCOM at the Chamber of Industry and Commerce), Compiègne (UTC, University of Technology), Paris (ESDI Design School)</footnote>
<figure><img src="image_118.png" /><figcaption>(a)</figcaption></figure>

<caption>(b)</caption>

<caption>(c)</caption>

Figs. (a) Stem of an Opuntia-cactus with leaves removed. The pattern may be interpreted as the buckling of a cylinder. (b) 'Automorphic tube', experimental structure designed by the french engineer Robert LE RICOLAIS (about 1960). The 'harmonic' buckling is due to strong axial compression. (c) Folded structure obtained from a single sheet, designed by Nathalie MAILLARD, student in Experimental Design at SUPINFOCOM, Valenciennes (1991). For complete stabilization, the cylinder is combined with an interior tube presenting axial folds.

References:

R.C. CHAPLIN, J.E. GORDON, G. JERONIMIDIS (1983): *Composite Material*, U.S. Patent 4,409,274

B. KRESLING (1992 a): *La Bionique - Nouveaux Concepts pour le Design*, in Design Recherche Revue, 1, 51-68, A Jour (Ed.), Paris

B. KRESLING (1992 b): *Folded Structures in Nature - Lessons in Design*, in: SFB 230 - Natürliche Konstruktionen, 7, Proc. of the Internat. Symp. of the Sonderforschungsbereich 230, Universität Stuttgart, oct. 1-4 1991, Part 2, 155-161

B. KRESLING (1993): *Folds*, in: *Bionics, Nature as a Model*, Pro Futura (Ed.) München, 13-33

R. LE RICOLAIS (1935): *Les tôles composées et leurs applications aux constructions légères*, in: Bull. Ing. Civils de France (mai - juin 1935), 410-431

K. MIURA (1989): *Folding a Plane - Scenes from Nature, Technology and Art*; in: G. DARVAS, D. NAGY (Ed.): *Symmetry of Structure*, Interdisc. Symp. Budapest, Hungary; Aug. 13-19, 1989, 391-394

W. NACHTIGALL, B. KRESLING (1992): *Baupomen der Natur - Teil I: Technische Biologie und Bionik von Knoten-Stabtragwerken*, in: *Naturwissenschaften* 79, 193-201; *Baupomen der Natur - Teil II: Technische Biologie und Bionik von Platten-und Falt-Konstruktionen*, in: *Naturwissenschaften* 79, 251-259, Springer, Heidelberg