bluuebunny/crossref_metadata_2025 huggingface dataset:
REGENERATION IN ROOT CUTTINGS OF TARAXACUM OFFICINALE I. THE NATURE AND LEVELS OF ENDOGENOUS HORMONES
Authors: BOOTH A. , SATCHUTHANANTHAVALE R.
Published: May 2006

The levels of auxins, cytokinins and gibberellins in extracts of fresh roots of Taraxacum were estimated by bioassay after chromatography. Auxin activity, largely confined to a single zone on chromatograms, had the RF and chromogenic properties of IAA and ranged from 45 to 85 μg kg‐1 fresh weight of roots (in IAA equivalents). Similar auxin activity was found in root diffusates collected in agar gel. Most of the cytokinin activity was present in the zone RF 0.6‐0.8 on chromatograms developed in a n‐butanol: acetic acid: water solvent. The cytokinin was not characterized but its level in kinetin equivalents was in excess of 500 μg kg‐1 fresh weight of roots. Gibberellin activity was of the order of 1 μg kg‐1 in GA3 equivalents.
AGEING IN EXCISED ROOTS OF TOMATO II. THE EFFECTS OF GROWTH HORMONES ON AGEING IN GLUCOSE
Authors: WESTON GEOFFREY D.
Published: May 2006

Culture of roots for 7 days in 1.5% glucose medium drastically enhanced ageing on subsequent subculture in 1% sucrose medium. NAA, GA, BA, ABA and ethylene enhanced the ageing of roots cultured in 1% sucrose medium, but counteracted the effect of pretreatment in 1.5% glucose. Reduction of growth during the glucose pretreatment by low temperature counteracted the effect of glucose on ageing; in contrast, reduction of growth by a high concentration of mannitol did not affect ageing. Exposure of roots to glucose for 72 h was required to produce the effects of glucose. It is postulated that cell division may be required during the glucose treatment for glucose to affect ageing.
FURTHER STUDIES ON POLLINATION ECOLOGY IN FICUS SYCOMORUS II. POCKET FILLING AND EMPTYING BY CERATOSOLEN ARABICUS MAYR
Authors: GALIL J. , EISIKOWITCH D.
Published: May 2006

Filling of pockets with pollen by the agaonid wasp Ceratosolen arabicus Mayr (Chalcidoidea, Hymenoptera) was studied in Ficus sycomorus L. at Magadi, Kenya. The phenology of the fig during the male phase (D) was observed in detail and various techniques were devised in order to ensure the normal behaviour of the wasps in spite of the bisection of the fig and the strong illumination necessary for carrying out the observations. It was found that in fig‐halves tightly enclosed with cellophane paper during the second morning of the male phase, the emerging wasps filled their pockets with pollen from anthers previously detached by the male wasps. It was established that the cutting of anthers is a separate, specific action and not merely a byproduct of the tunnelling of the syconial wall that takes place afterwards. In the filling act itself, the role of the combs–rows of stiff bristles along the inner margin of each foreleg coax was established. Pollen was lifted by the arolia of the forelegs from the open anthers to the underside of the thorax and shovelled from there by the coxal combs into the thoracic pockets which gaped widely due to the bending of the body.

An analysis of the responses of the wasps to various environmental conditions leads to the conclusion that the size of the cavity is a critical factor in the behaviour of the wasps in the fig of F. sycomorus. The possible role of light for pocket filling in the subdued illumination of the intact fig cavity is discussed.
EVIDENCE FOR THE PRESENCE OF A ‘FACTOR’ IN ELYSIA VIRIDIS WHICH STIMULATES PHOTOSYNTHATE RELEASE FROM ITS SYMBIOTIC CHLOROPLASTS
Authors: GALLOP ANGELA
Published: May 2006

Tissues of Elysia viridis contain a ‘factor’ which stimulates release of fixed 14C from isolated Codium chloroplasts and also from the symbiotic algae of Anemonia sulcata. This ‘factor’ appears to be thermolabile, non‐particulate, and only occurs in effective amounts in the chloroplast‐containing tissues of the animal. So far, attempts to mimic the action of Elysia homogenates by varying the pH of the medium, or by adding Codium homogenates, fructose 1,6 di‐phosphatase or‘2C‐glucose to it, have failed.
LIPID METABOLISM IN LEAVES OF TUSSILAGO FARFARA DURING INFECTION BY PUCCINIA POARUM
Authors: LÖSEL D. M. , LEWIS D. H.
Published: May 2006

Following infection by Puccinia poarum, there is an accumulation of lipid in leaf tissue of Tussilago farfara. Most of this increase is in the fungus, which accounts for nearly half of the dry weight of mature aecial pustules. While the lipid content of infected tissue rises to more than three times that of healthy leaves, that of the uninfected parts of diseased leaves is reduced by one‐third. Aerial pustules accumulate a high proportion of neutral lipid, particularly triglycerides and fatty acids. As infection progresses, a loss of chloroplast glycolipids and phosphatidyl glycerol is accompanied by increases in phosphatidyl ethanolamine and phosphatidyl choline and the formation of phosphatidyl serine, which is not readily detectable in healthy leaf tissue. The lipid changes following rust infection have been compared with those of senescing Tussilago leaves.

Both neutral lipids and phospholipids incorporated more photosynthetically assimilated C in rust‐infected tissue than in healthy leaves. Greatest differences were in free fatty acids, triglycerides, phosphatidyl ethanolamine and phosphatidyl choline with significant increases also in sterols, phosphatidyl inositol and phosphatidyl serine. Whereas three‐quarters of the activity incorporated from 14CO2 into lipid appears in the neutral lipids of diseased tissue, in healthy tissue these contain only one‐quarter.
A COMPARISON OF NEGATIVE RELATIVE GROWTH RATES IN SHADED SEEDLING
Authors: MAHMOUD A. , GRIME J. P.
Published: May 2006

Seedlings of the shade‐tolerant species, Deschampsia flexuosa, were subjected to shade treatments under controlled conditions of daylength, temperature, irradiance, relative humidity and mineral nutrient supply. Dry matter production was compared with that of seedlings of the shade‐intolerant species, Agrostis tennis and Festuca ovina. The three species did not differ markedly with respect to their light intensity compensation points. A more promising explanation for the shade tolerance of Deschampsia flexuosa lies in the extremely low negative relative growth rates which seedlings exhibit at light intensities below the compensation point.
GROWTH CHARACTERISTICS OF THE‘ROGUE’TOMATO
Authors: CALVERT A.
Published: May 2006

Summary

A faster than normal rate of leaf production in the rogue tomato leads to earlier flowering in summer. In winter, growth of the inflorescence is less than the normal, often resulting in abortion.

In the rogue there is an early short‐term stimulation of growth of all axillary buds. This, together with a smaller leaf area and shorter internodes, creates the characteristic rogue appearance. In general, however, the pattern of axillary growth along the stem is similar in rogue and normal plants; an observation which provides little support for the theory that the rogue appearance is due to loss of apical dominance.

Neither removal of the first two leaves nor IAA application influences the rate of leaf initiation in the rogue as it does in the normal, indicating the possibility that the rogue has a modified auxin control system.
PLANT GROWTH RESPONSES TO VESICULARARBUSCULAR MYCORRHIZA
Authors: HAYMAN D. S.
Published: May 2006

Summary

Light and temperature greatly influenced the development of vesicular‐arbuscular mycorrhiza and growth of onions in a phosphate‐deficient soil. There were more large arbuscules and host growth was stimulated more with 25,000 lux than with 13,000 lux at 23° C and in a 14‐23° C diurnal cycle. At 14° C and 13,000 lux mycorrhiza caused no growth stimulation even in three low‐phosphate soils. At 18° C infection was much sparser in a 6 h daylength than in 12 and 18 h. Mycorrhizal Plants kept in daylengths of 6 h at 13,000 lux were 3.5 times heavier than their non‐inoculated controls. The effect of infection increased in longer daylengths and higher light intensities to 14.2 times the weight of controls with 18 h at 25,000 lux. The addition of soluble phosphate stimulated growth to the same extent as mycorrhizal inoculation did in the highest light conditions but phosphate stimulated growth more than did mycorrhiza under intermediate light conditions. The amounts of soluble carbohydrate in the roots of Plants given phosphate and in those that were mycorrhizal did not differ significantly, but there was more soluble carbohydrate in Plants growing in most light. Plants both with and without mycorrhiza contained much glucose, fructose, sucrose and an unidentified sugar with a low RF value, but there was no indication of fungal carbohydrates such as trehalose and mannitol.
TETRAD POLLEN GRAIN DEVELOPMENT AND STERILITY IN LESCHENAULTIA FORMOSA (GOODENIACEAE)
Authors: KNOX R. B. , FRIEDERICH E.
Published: May 2006

Summary

Pollen of Leschenaultia formosa R. Br. adheres as tetrads linked together on their radial walls by extensions of the bacular strands of sexine sporopollenin after release from the meiotic tetrad. Before release, the tetrads of microspores showed a thickened deposition of primexine polysaccharide on their radial walls, where only slight callose deposits were detectable.

The onset of variable sterility in the tetrads was detected as early as the prevacuolate period after spore release. Sterile microspore protoplasts could not he plasmolysed and using the fluorochromatic reaction, showed leakage of fluorescein through the plasma membranes. Sterile grains showed considerable exine development and patterning, which continued until midvacuolate period, but the inner cellulosic intine, layer was absent. In the walls of fertile grains, the enzymic proteins, acid phosphatase and ribonuclease were located in the intine, as found previously with other pollens.
THE UPTAKE AND TRANSLOCATION OF 35SO2 IN SOY‐BEAN GLYCINE MAX VAR. BILOXI
Authors: GARSED S. G. , READ D. J.
Published: May 2006

Summary

Feeding of specific leaves has been used to follow the uptake and translocation of 35SO2 in soy‐bean plants at the four‐leaf stage. The effect of leaf age and position on the translocation pattern have been examined and an analysis made of the distribution of radioactivity with time. The results are discussed with reference to data for movement of 14CO2 and foliar applied 35SO2‐4, and to the ecological implications.
THE RELATIONSHIP BETWEEN TEMPERATURE AND SEEDLING GROWTH OF TWO SPECIES WHICH OCCUR IN UPPER TEESDALE
Authors: ARNOLD SYLVIA M.
Published: May 2006

Summary

Seedlings of Plantago maritima L. and Kobresia simpliciuscula (Wahlenb.) Mackenzie were grown at 10, 14, and 18° C. Net assimilation rate and relative growth rate of Plantago seedlings increased with temperature, as did rate of leaf extension, and there was little delay in leaf emergence as temperature dropped from 18 to 10° C. Increase of temperature from 10 to 14° C had little effect on Kobresia seedlings, but growth increased significantly with a further rise to 18° C. Rate of leaf extension was unaffected by temperature but leaves grew for a shorter time, and emergence was greatly delayed at the lower temperatures. Increase in total leaf length with temperature was attributable to increase in number of leaves in Kobresia, and increase in average leaf length in Plantago. In both species successive leaves elongated at a similar rate, and temperature had no effect on leaf width. Growth responses are discussed in relation to temperature regimes measured in Teesdale.
DIFFERENCES IN XYLEM EXUDATION BY SEMINAL ROOTS OF LOLIUM VARIETIES
Authors: DUNLOP JAMES
Published: May 2006

Exudation by excised roots of eleven Lolium varieties has been studied. Data on the rate of potassium translocation, the rate of water movement through the roots, the concentration of potassium in the xylem exudate, the electrical potential gradient across the roots, and the electrochemical potential difference for potassium across the roots is reported. Each parameter showed significant variation among the varieties with only water flux grouped according to species. It is suggested that the variation in rate of potassium translocation can be attributed partly to differences in the rate of water movement through roots and partly to differences in the intensity of transport to the xylem.
ELECTRON MICROSCOPICAL STUDIES OF THE MICROFLORA OF ROOTS OF SAND DUNE GRASSES
Authors: Old K. M. , NICOLSON T. H.
Published: May 2006

Scanning and transmission electron microscopy were used to study microflora of roots of three species of sand dune grasses. Observations were made on the mucigel on intact epidermal cells and the colonization of sloughing superficial root cells by bacteria and actinomycetes. Thin sections of the same root samples showed that bacteria penetrated epidermal cells either by perforating the cell wall or by exploiting the middle lamella between adjacent cells as an avenue of entry. Cortical cells of all three species contained vesicular‐arbuscular endophytes. Several phases of the mycorrhizal association could be identified.
MIMULUS IN GREAT BRITAIN‐A CYTOTAXONOMIC NOTE
Authors: PARKER P. F.
Published: May 2006

The chromosome numbers and external morphology of Mimulus naturalized in Britain are compared with those of experimentally produced F1 hybrids between Mimulus guttatus DC. and M. luteus L.
LEAKAGE DURING IMBIBITION, RESISTANCE TO DAMAGE AT LOW TEMPERATURE AND THE WATER CONTENT OF PEAS
Authors: SIMON E. W. , WIEBE H. H.
Published: May 2006

The extent of leakage from imbibing pea embryos depends on their initial water content, leakage being very low if the embryos already have a water content of 30% or more (water potential higher than −80 bars). Seeds that have reached this degree of hydration are killed by a 20‐min exposure to liquid nitrogen.
A THEORETICAL ANALYSIS OF THE CONTRIBUTION OF ALGAL CELLS TO THE ATTENUATION OF LIGHT WITHIN NATURAL WATERS I. GENERAL TREATMENT OF SUSPENSIONS OF PIGMENTED CELLS
Authors: KIRK J. T. O.
Published: May 2006

A theoretical treatment of light attenuation within suspensions of phytoplankton, which takes account of the heterogeneous distribution of pigment in the system, is described. As a measure of the effect of canopy structure on light attenuation, a new parameter, the penetration coefficient (Pλ) is introduced, this being defined as the ratio of the downward monochromatic radiation flux at a given depth in the suspension to that within an equivalent solution of the algal pigments. A set of rules is established, applicable to cells of any shape or orientation, which characterizes the relationship between the penetration coefficient and the parameters of canopy structure (cell number, size, pigment composition etc.). A standardized procedure for calculating the spectral distribution of, and the vertical attenuation coefficients for, photo‐synthetically active radiation within model phytoplankton suspensions, is outlined.
A THEORETICAL ANALYSIS OF THE CONTRIBUTION OF ALGAL CELLS TO THE ATTENUATION OF LIGHT WITHIN NATURAL WATERS II. SPHERICAL CELLS
Authors: KIRK J. T. O.
Published: May 2006

A theoretical treatment of light attenuation within natural phytoplankton suspensions, developed in a previous paper, has now been applied to model suspensions of green and blue‐green algal cells and colonies, in order to obtain a quantitative assessment of the effects of changes in the phytoplankton canopy structure on light attenuation within the system. It is shown that for green algae suspended in water in which effectively all the blue light is removed by dissolved yellow substances (gelbstoff) the light attenuation properties of the suspension are rather similar to those of an equivalent solution of algal pigments: this is because the individual cells have relatively low absorption values in the spectral region (545–655 nm) in which most of the transmitted light occurs. With blue‐green algae, which have a strong absorption in this region, there can be marked differences between the light attenuation properties of suspensions and of equivalent pigment solutions. The suspensions transmit substantially more photosynthetically active radiation than the solutions: the effect increases with cell/colony size, with algal concentration and with depth, and can amount to a difference of several‐fold. Values of vertical attenuation coefficients, and increments in attenuation coefficients per unit algal concentration, for the photosynthetic waveband have been calculated, and their dependence on pigment composition and cell/colony size is demonstrated. Calculations have also been carried out to show the relationship between the phytoplankton canopy structure, and the euphotic depth and maximum sustainable standing crop, of the suspension.
THE INFLUENCE OF LIGHT ON STOMATAL DENSITY IN THE TOMATO
Authors: GAY A. P. , HURD R. G.
Published: May 2006

Stomatal densities (stomatal number per unit leaf area) were determined on tomato plants grown at ‘high’ (100 W m−2) and ‘low’ (20 W m−2) light in a growth cabinet. The upper epidermis of a fully expanded leaf in low light had fewer than one stoma mm−2, whilst that in high light had thirty stomata mm−2. On the lower epidermis there were about eighty and 100 stomata mm−2 in low and high light respectively. Similar differences were observed on plants growing in natural light.

Stomatal initiation is most active early in the development of the leaf and effects of light on initiation were greatest at this stage, being observable within 3 days of a change in light level. Since light influenced the rate and duration of all stages of leaf expansion, the final stomatal densities achieved under natural conditions varied with the light history of the leaf.

Stomatal density reached a peak before the leaf had expanded to 10% of its final area. Stomatal initiation and stomatal density both decreased from then until leaf expansion ceased. Fully‐expanded leaves of plants grown continuously in the same environment had similar stomatal densities irrespective of their position on the plant.

A quantitative relationship is described between stomatal density and leaf area during the growth of a leaf.
SOME ASPECTS OF TISSUE WATER RELATIONS IN THREE POPULATIONS OF EUCALYPTUS VIMINALIS LABILL.
Authors: LADIGES PAULINE Y.
Published: May 2006

Using the pressure bomb technique, measurements have been made of the tissue water relations of seedlings of three populations of Eucalyptus viminalis, and of adult shoots of trees from two contrasting sites, to facilitate an understanding of the physiological basis of intra‐specific variation in drought resistance.

For both juvenile and adult material, the shoot water potential of the most drought resistant population declined most rapidly with decreasing water content. Estimates of the fraction of water in the cell walls at full turgor were also greatest for this population, averaging 0.36 for juvenile and 0.40 for adult material. Calculated values for the bulk modulus of elasticity of the walls were very variable, but tended to be higher, in adult than juvenile tissues.

The results suggest that in dry habitats there has been selection for plants which, during temporary periods of drying, can maintain a water content above the critical level for cell damage. Differences between two very closely situated field populations emphasize the need to consider the role of edaphic as well as climatic factors in selection for drought resistance.
THE EFFECT OF SALT AND OSMOTIC STRESS ON THE RETENTION OF POTASSIUM BY EXCISED BARLEY AND BEAN ROOTS
Authors: NASSERY H.
Published: May 2006

The effect of different concentrations of NaCl, mannitol and CaCl2 on the retention of potassium ion by preloaded roots of barley, Hordeum vulgare, and bean, Phaseolus vulgaris, indicated that 50 mM NaCl had no effect on potassium loss, but 50 mM NaCl or more increased the rate of efflux. Barley roots appeared 10 be more sensitive to salt stress than bean roots since 100 mM NaCl caused 78% potassium loss over 6.5 h by barley as compared with 40% loss by bean roots. Mannitol up to 200 mM had no effect on the retention of potassium by barley roots but slightly increased the potassium loss from bean roots (26%). The results suggested that salt stress is more effective than osmotic stress in disrupting the membrane permeability and calcium ions can prevent the increased permeability caused by osmotic or ionic stress.
INHIBITION OF SEED GERMINATION UNDER LEAF CANOPIES IN ARENARIA SERPYLLIFOLIA, VERONICA ARVENSIS AND CERASTUM HOLOSTEOIDES*
Authors: KING T. J.
Published: May 2006

The germination of imbibed seeds of Arenaria serpyllifolia L., Veronica arvensis L. and Cerastium holosteoides Fr. is inhibited under two layers of Tilia×europaea L. leaves. The ecological significance of this phenomenon is discussed.
SOME ASPECTS OF HETEROSTYLY
Authors: YEO P. F.
Published: May 2006

It is suggested that the functional significance of each di/trimorphic structure in heterostyled flowers should be considered separately. The origin of the morphological and physiological components of heterostyly is discussed; it is suggested that the physiological incompatibility arose first and created conditions favouring selection of morphological differentiation. In this connection, the cases of Amsinckia and Narcissus tazetta are given special consideration. The restricted occurrence of tristyly is considered together with the distinctive syndrome of exserted sexual organs and sternotribic pollination in heterostyled plants. The need is emphasized to bear in mind constantly the functional aspects of heterostyly.
RADIOCARBON DATES FROM LATE‐DEVENSIAN DEPOSITS, NANT FFRANCON, CAERNARVONSHIRE
Authors: BURROWS C. J.
Published: May 2006

Two radiocarbon dates near the beginning and end of the Allerød interstadial (conventional pollen zone II) show that the timing for the event in the mountains of North Wales was similar to that elsewhere in Britain and Europe. The occurrence of a pre‐Allerød interstadial, almost certainly equivalent to the Bølling (conventional pollen zone Ib), is confirmed. Other sequences for the same period from lowland North Wales and elsewhere in Western Britain differ from the Nant Ffrancon sequence in that evidence for cooling between the Bølling and Allerød is missing, but some sequences from inland mountainous areas, or in Eastern Britain and the Continent are very similar to the Nant Ffrancon sequence.
Studies ON ENDOGENOUS LEVELS OF ETHYLENE AND AUXIN IN VICIA FABA DURING GROWTH AND DEVELOPMENT
Authors: EL‐BELTAGY A. S. , HALL M. A.
Published: May 2006

Endogenous levels of ethylene, auxins and inhibitors have been followed during the course of development in two varieties of Vicia faba having markedly different growth habits. Increases in internal ethylene levels correlate well with the time of abscission of flowers or pods. No clear correlations were observable between any particular developmental process and endogenous levels of auxin or inhibitors, although there was some correlation between inhibitor levels and abscission. The role in the control of development of the three types of growth regulator studied is discussed.
ZINC AND COPPER UPTAKE BY AGROSTIS STOLONIFERA, TOLERANT TO BOTH ZINC AND COPPER
Authors: WU LIN , ANTONOVICS JANIS
Published: May 2006

Zinc and copper uptake by Agrostis stolonifera, tolerant to both zinc and copper, showed that different zinc levels had no effect on copper uptake and, conversely, copper had no effect on zinc uptake. There was, however, a strong interaction in the toxic effects of zinc and copper as measured by root elongation. The mechanisms of zinc and copper tolerance are therefore independent even when they act in the same individual.
I. NUMERICAL ANALYSIS
Authors: PENNINGTON WINIFRED , SACKIN M. J.
Published: May 2006

Results are presented from Principal Components Analysis of three data matrices (pollen concentration per c.c., percentages of total pollen, and analyses for eight or nine chemical elements) of c. thirty samples from each of two profiles of lake sediment of Late‐Devensian age (15000 to 10000 years B.P.) from the Lake District and N.W. Scotland. The groupings of samples by their scores on the first two components of these Principal Components Analyses have been shown to produce similar divisions (zonations) to those originally produced subjectively by inspection of the percentage pollen diagrams. Though neither profile includes the classical Late‐Weichselian oscillation of pollen zones I, II and III, involving expansion of percentages of birch pollen within biogenic sediment between two minerogenic layers, numerical analysis has revealed in the data from both sites a pattern involving a threefold division with revertence, and another pattern of twofold division. The subjective zonation of the percentage diagrams clearly involved a process of mental integration of these two patterns. A plot of the scores of the samples on the first two components of the Principal Components Analyses groups the samples into clusters corresponding with the zones determined by inspection; similar results are obtained for each of the three Principal Components Analyses. This is interpreted as indicative of a close relationship between pollen and chemical data which can most readily be explained on the hypothesis that the boundaries of pollen zones represent the results of environmental changes which simultaneously affected soils and vegetation.
THE EFFECTS OF SENESCENCE ON THE PROTEIN COMPLEMENT OF PLASMA MEMBRANES FROM COTYLEDONS
Authors: LEES G. L. , THOMPSON J. E.
Published: May 2006

The protein composition of plasma membranes from young and senescent cotyledons of germinating Phaseolus vulgaris has been analysed by polyacrylamide gel electrophoresis after solubilizing the membranes in sodium dodecyl sulfate. Gels for membrane from 2‐day‐old tissue, an age still largely unaffected by senescence, showed eighteen bands ranging in molecular weight from 12,000 to 150,000. Of these, nine were sufficiently intense to register in spectrophotometric scans. Two fast‐running proteins of molecular weights 12,000 and 26,000 were quantitatively preponderant at this stage and comprised 11 and 25% of the total membrane protein respectively. With the onset of senescence during late germination the protein banding pattern changed. The sharp clearly defined bands characteristic of gels from young membrane were replaced by broad diffuse regions of protein stain in the gels from senescent membrane. In addition, the number of protein bands seen in the gels decreased between days 2 and 9 of germination. These observations suggest that membrane senescence in cotyledons is mediated, at least in part, by cytosol proteases acting on membrane proteins. Such action would lead to complete breakdown of some proteins and alteration of others.
HEXOKINASE ACTIVITY IN CULTURED SYCAMORE CELLS
Authors: FOWLER MICHAEL W. , CLIFTON ANNE
Published: May 2006

Cells of sycamore (Acer pseudoplatanus) grown in batch culture were disrupted by ultrasound. Slight variation in the length of time for which ultrasound was applied was found to produce major alterations in the ratio of ‘particulars’ to ‘soluble’ hexokinase activity. Variations in this ratio were also observed when the osmolarity of the extraction medium was maintained by the use of either Ficoll and Dextran 40 or mannitol. Growth of the cells was also accompanied by changes in the ratio of ‘particulate’ to ‘soluble’ hexokinase activity. The data provide confirmatory evidence that a proportion of the total hexokinase activity of the cell is associated with a particulate fraction but there is no evidence of its association with the cell wall.
SHADE‐INDUCED DAMPING‐OFF IN CONIFER SEEDLINGS
Authors: TAHER M. M. , COOKE R. C.
Published: May 2006

The mortality of seedlings of Pinus sylvestris, P. contorta, Picea sitchensis and P. exceha grown in natural soil under a range of light intensities was recorded over a 90‐day period. Low light intensities favoured damping‐off by soil‐borne necrotrophic fungi, principally species of Fusarium and Pythium, but aseptically‐grown seedlings survived a similar 90‐day period at these low intensities. The two Pinus species were more susceptible to damping‐off than the Picea species under all light treatments used but this difference was most marked at low light intensities. The influence of low‐light regimes on host‐necrotroph interactions is discussed.
SHADE‐INDUCED DAMPING‐OFF IN CONIFER SEEDLINGS
Authors: TAHER M. M. , COOKE R. C.
Published: May 2006

Seedlings of Pinus sylvestris and Picea sitchensis were grown aseptically in sand culture for 30 days under a range of light intensities. Relative growth rates (whole seedlings and shoots) of Pinus sylvestris were greater than those of Picea sitchensis and significantly so at low light intensities, but their carbohydrate status was lower. The ethanol‐soluble carbohydrate/ethanol‐insoluble carbohydrate ratio was always higher in Pinus sylvestris than in Picea sitchensis and epidermal cell walls, lignification and vascularization in the hypocotyl were much less developed in Pinus sylvestris than in Picea sitchensis, especially at low light intensities. These findings are discussed in relation to the established susceptibility of Pinus sylvestris and resistance of Picea sitchensis to shade‐induced damping‐off by necrotrophic fungi.
THE EXTENSION ZONE OF MYCELIAL HYPHAE
Authors: STEELE G. C. , TRINCI A. P. J.
Published: May 2006

The lengths of the apical tapered region (the extension zone) of leading hyphae of six species were determined. Although the extension zones of different types of hyphae of Neurospora crassa varied from 2.2 to 29.2 μm, their extension zone expansion times (the time taken for a hyphal tip to expand from its minimum to its maximum diameter) were very similar. There was a direct relationship between extension zone length and the rate of hyphal extension. Extension zone length and hyphal diameter were not affected by temperature.
SCAPE ELONGATION IN NARCISSUS: THE INFLUENCE OF FLORAL ORGANS
Authors: HANKS GORDON R. , REES A. R.
Published: May 2006

To study the effects of floral organs on scape growth of narcissus, the spathe, perianth parts, paracorolla, anthers and gynoecium were excised from the bud in all practicable combinations, and growth regulators were applied to decapitated scapes.

Spathe removal induced earlier flowering, and by the third day after treatment had reduced scape growth to 88% of that of intact controls. The removal of other parts (alone or in combination) had no additional effects on scape growth, except for gynoecium removal which reduced growth to 43% of that of intact controls after 3 days. Scape growth continued in all treated plants, however, and by day 23 the decapitated plants had grown 79% as much as the intact controls. The effect of gynoecium removal could largely be replaced by applied auxin; gibberellic acid was partly effective in restoring scape growth.
A NOTE ON ELLAGITANNINS AS INDICATORS OF EVOLUTIONARY STATUS IN DICOTYLEDONS
Authors: SPORNE KENNETH R.
Published: May 2006

Statistical analysis confirms that, among dicotyledons, not only are leuco‐anthocyanins correlated with primitive characters but so, also, are ellagitannins. The most primitive dicotyledons, and especially those in tropical rain‐forests, tend to possess both kinds of tannin while the most advanced lack both kinds.
STIMULATION OF SEX ORGAN FORMATION IN PHYTOPHTHORA BY ANTAGONISTIC SPECIES OF TRICHODERMA
Authors: BRASIER C. M.
Published: May 2006

Two methods are described for the induction of sex organ formation in heterothallic Phytophthora species in response to Trichoderma, a volatile method and a direct inoculation (‘contact’) method.

Tested for their ability to induce sexual reproduction in Phytophthora, isolates of Trichoderma koningii, T. piluliferum, T. polysporum and T. viride were found to be active, and isolates of T. hamatum, T. harzianum, T. longibrachiatum and T. pseudokoningii inactive. Response in Phytophthora was, without exception, confined to the A2 compatibility type. Response of different Phytophthora species, however, was more variable. All forty‐one isolates of P. cam‐bivora and P. cinnamomi tested responded to Trichoderma viride. Isolates of Phytophthora cryptogea, P. drechsleri, and P. nicotianae were apparently polymorphic for response. The black pepper form of P. palmivora responded, whereas P. palmivora forms 1 and 2 did not. A minimum induction period of c. 24 h exposure to volatiles of active Trichoderma was apparently necessary for consistent oogonial formation to occur. Oogonial formation occurred on a range of sterol‐containing media but not in their absence and over a wide range of conditions of temperature and light.

Antagonism of Phytophthora cultures by active Trichoderma isolates was readily apparent both in the volatile and contact methods. The ability of Trichoderma isolates to induce a sexual response in Phytophthora was correlated with their ability to produce volatile antibiotics. Possible implications of the ‘Trichoderma effect’ for the taxonomy, reproductive physiology and genetics of Phytophthora spp. are considered.
STRUCTURE OF AERIAL AND SUBMERGED SCLEROTIA OF COPRINUS LAGOPUS
Authors: WATERS H. , BUTLER R. D. , MOORE D.
Published: May 2006

Sclerotia were formed in both aerial and submerged parts of the mycelium. In addition a layer of cells with pigmented thick walls (called brown matting) which differentiated at the air/agar interface was interpreted as an aspect of sclerotial behaviour since it was regularly formed by strains which produced submerged sclerotia and was composed of cells of similar structure to those of the outermost layer of the submerged sclerotium. Apart from producing sclerotia and oidiospores the cells of the aerial mycelium remained undifferentiated. In contrast, cells of the submerged mycelium, though initially indistinguishable from those of aerial hyphae, became individually differentiated within about 5 days of growth producing two further novel cell types; inflated cells containing glycogen, and hyaline thick‐walled cells. Submerged sclerotia were pale brown in colour, irregularly shaped and about 0.5–1.0 mm in diameter. The only structure which differentiated the submerged sclerotium from the submerged mycelium was the outer rind, a layer of cells with thick, pigmented walls. The central (medulla) region contained the same cell types in the same frequencies as the general submerged mycelium. In sharp contrast the aerial sclerotia were highly organized structures composed of distinct and compact tissues. Mature aerial sclerotia were dark brown to black spheroidal structures up to 0.5 mm in diameter. An outer layer of dead and moribund hyphae surrounded the main body of the sclerotium which was bilayered with an outer rind and inner medulla. The rind was multilayered and consisted of small cells with thick pigmented walls; intercellular spaces were cuticularized. The medulla was a closely packed tissue composed predominantly of hyaline thick‐walled cells of the same type as were encountered in the submerged mycelium.
THE GROWTH OF SECONDARY WOOD FIBRES
Authors: WENHAM M. W. , CUSICK F.
Published: May 2006

Cambial derivatives differentiating as xylem fibres characteristically increase in length by intrusive growth. Radial expansion of contiguous cells is required for this intrusive growth which, in consequence, is restricted to the expansion zone of the newly formed wood. The amount of intrusion depends primarily on the position of the tip of a fibre in relation to the lines of junction of tangential and radial walls in the surrounding cells; these lines of junction are potential sites for intrusive growth. In general, the greatest intrusion occurs where there are two potential sites for intrusion (usually one on either radial face of the fibre's tip); tips with one site show less intrusive growth and those with none show least of all. These arrangements may be modified by the configuration and activity of neighbouring cells.

The hypothesis formulated is that the tip of a fibre secretes an enzyme which weakens the middle lamella between the cells adjacent to it; where this occurs, these cells, during their turgor expansion, round off from each other at the corners. The thin–walled tip of the fibre fills this space as it is created. The notion that the intruding tip pushes its way into the cellular matrix is contested.
THE RELEASE OF SPERMS FROM THE ANTHERIDIA OF POLYTRICHUM JUNIPERINUM HEDW.
Authors: PAOLILLO D. J.
Published: May 2006

The release of sperms from an antheridium of Polytrichum juniperinum occurs in two phases: a rapid phase, completed within a few seconds, and a slow phase, usually completed in 1–5 min. The rapid phase depends on an elastic contraction of the jacket that forces all or most of the sperms out of the chamber. The contraction has this effect because the base of the chamber contains a fluid that accounts for more than half the volume of the chamber. The fluid accumulates during maturation of the antheridium, and the jacket is stretched, storing the potential energy required for the expulsion of the sperms. The rapid phase of sperm release occurs in hypertonic solutions and in petroleum jelly, which confirms that the uptake of water by the antheridium is not required for the opening of the antheridium. The slow phase of release is distinguishable only when a substantial residue of sperms remains after the rapid release, and can be prevented by high osmotic concentration in the bathing medium. The slow release probably depends on the net uptake of water by osmosis, resulting from the relatively high osmotic concentration of the fluid in the antheridial chamber.
THE CLIMATIC CONTROL OF THE ALTITUDINAL DISTRIBUTION OF SEDUM ROSEA (L.) SCOP. AND S. TELEPHIUM L.
Authors: WOODWARD F. I.
Published: May 2006

It has been demonstrated that the decrease of temperature associated with an increase in altitude of 250 m is sufficient to reverse the outcome of competition between Sedum rosea (L.) Scop, and S. telephium L. ssp. fabaria Syme.

Growth analyses of S. rosea and S. telephium in a range of temperature conditions have shown that the change in the outcome of competition is due to the marked increase in growth of 5. telephium and the insensitivity of s. rosea to an increase in temperature over the range recorded in the field.
SOME STATISTICAL PROBLEMS ASSOCIATED WITH DETERMINATIONS OF POPULATION PARAMETERS FOR HERBACEOUS PLANTS IN THE FIELD
Authors: HUTCHINGS M. J.
Published: May 2006

The use of regressions to predict weights of plants and methods for the assessment of skew‐ness of weight and height distributions in populations of Mercurialis perennis (L.) are discussed. Regression methods for estimation of plant weight are non‐destructive so that several weight estimates can be made at intervals on growing plants. Highly accurate predictions can be made from relationships between weight and dimensions. Non‐linear (quadratic) regressions based on the relationship between weight and hd2 (where h= stem height; d= basal stem diameter) were found to be most accurate in weight prediction. Use of the estimate of relative error to determine error in prediction is considered; when errors are normally distributed and emphasis is placed upon mean weights rather than individual weights, the degree of error is considerably reduced. Because the relationship between weight and hd2 changes during the season, a sequence of regressions should be used for weight prediction. The relationship may be disturbed through time by environmental fluctuations and will vary spatially with habitat and genotype. The problem of inflexions in the use of quadratics is encountered and a solution suggested which assumes that other regressions without inflexions in the sequence are correct.

Histograms of weight and height distributions in plant populations do not allow accurate monitoring of changes in distribution through time. The moment coefficient is suggested as the best numerical estimate of skewness, since it is a sensitive measure and all the available data is utilized in its calculation. Pearson's second coefficient is less sensitive, and only utilizes the population mean and its median–a statistic which may be not sufficiently representative of the whole population to use in the calculation of skewness. Reasons are presented for the differences in the skewness values obtained by using these two coefficients.
THE RELEASE OF ORGANIC SUBSTANCES BY CEREAL ROOTS INTO SOIL
Authors: BARBER D. A. , MARTIN J. K.
Published: May 2006

Wheat and bailey plants were grown for 3 weeks in a constant environment chamber containing approximately atmospheric concentrations of carbon dioxide (0.03%) labelled with 14C. The roots of the plants were maintained under sterile or non‐sterile conditions in soil contained in sealed pots which were regularly flushed with air. This enabled the quantities of 14C‐labelled carbon dioxide produced in the soil by plant and microbial activity to be separately assessed. At harvest, the 14C and total carbon contents of the roots and shoots and of the water‐soluble and insoluble material present in the soil were measured.

These procedures enabled both the amounts of organic materials released into soil by the roots of growing plants and the effects of micro‐organisms on the process to be determined. Under sterile conditions between 5 and 10% of the photosynthetically fixed carbon may be released by roots compared with 12–18% by the roots of plants growing in unsterilized soil. These latter values are equivalent to 18–25% of the dry matter increments of the plants. The results indicate also that the increased evolution of carbon dioxide by cropped as compared to fallow soils can largely be ascribed to the immediate utilization by micro‐organisms of substances released by roots.
THE SYSTEMATIC POSITION OF HICKLINGIA EDWARDII KIDSTON AND LANG
Authors: EDWARDS DIANNE
Published: May 2006

Recent developments in the classification of the earliest vascular plants are discussed. The fertile parts of Hicklingia edwardii, a remarkably well preserved plant from the Middle Old Red Sandstone of Scotland, are described. It is concluded that this plant had lateral not terminal sporangia and may be assigned provisionally to the Zosterophyllophytina until more is known about its anatomy.
LEAF AIR SPACE SYSTEMS IN C3 AND C4 SPECIES
Authors: BYOTT G. S.
Published: May 2006

Measurements of airspace systems in monocotyledonous and dicotyledonous C3 and C4 leaves show that the C4 systems are generally smaller than those of C3 species. This anatomical feature is discussed in relation to PEP carboxylation and efficiency of water use.
ECOTYPE DIFFERENCES IN LEAF SURFACE PROPERTIES OF AGROSTISSTOLONIFERA FROM SALT MARSH, SPRAY ZONE AND INLAND HABITATS
Authors: AHMAD I. , WAINWRIGHT S. I.
Published: May 2006

Properties of the leaf surface associated with wettability were studied in ecotypes of Agrosti stolonifera from salt marsh, spray zone and inland habitats. The maritime ecotypes retained much less salt than the inland ecotype after immersion in salt water. Retention of salt after spraying was highest by leaves of the inland ecotype and least by those of the spray zone ecotype. Differences in retention of salt can be correlated with differences in wettability (indicated by measurement of advancing contact angle) and these differences are, in turn, related to differences in the structure and distribution of extracuticular waxes on the surfaces of leaves of the ecotypes. The differences are considered to be adaptations to the environments in which the ecotypes grow.
THE UPTAKE OF PARAQUAT BY SOIL FUNGI
Authors: SMITH S. N. , LYON A. J. E.
Published: May 2006

The mucoraceous fungi, Mucor hiemalis and Zygorhynchus heterogamous, are considerably more susceptible to paraquat than the imperfect species, Aspergillus niger and Penicillium frequentans. The inhibitory effect of increasing levels of paraquat on hyphal extension, dry matter production and spore germination are much more marked in Mucor and Zygorhynchus. When grown on media containing paraquat, the mycelia of these species contain approximately twice as much of the herbicide as those of Aspergillus or Penicillium. Feeding (14C‐methyl)‐paraquat confirms that twice as much activity is accumulated by the susceptible species. It is suggested that susceptibility to paraquat is associated with the degree to which the herbicide accumulates in the mycelium.
THE DEVELOPMENT OF PATTERNING IN THE ALVEOLAR SEXINE OF COSMOS BIPINNATUS
Authors: DICKINSON H. G. , POTTER URSULA
Published: May 2006

Development of the sexine component of the pollen wall of Cosmos bipinnatus has been examined in detail. The pattern is first generated in the peripheral spore cytoplasm by ribosome‐coated tubules of membrane, themselves apparently ordered by microtubules. This arrangement of membranous tubules moves to the plasma membrane upon the surface of which are formed ridges of fibrillar material, themselves in register with the tubules beneath. This fibrillar material is laid down heavily in the sites destined to be occupied by spines. The patterning of the ridges is not analogous with that of the sexine, but of the alveoli contained within it. The early sexine itself is formed from precursors secreted by the spore cytoplasm, which encase the fibrils and polymerize. On release of the young spores from the tetrad, the fibrillar content of the sexine is lost, forming the network of alveoli characteristic of this type of pollen wall. The sexine also expands at this point and, since the nexine does not and the two layers are firmly attached to each other at the apertures, this growth results in the bowing out of the sexine in the non‐aperatural regions and, thereby, the formation of the cavea.
ISOLATION, STABILITY AND BIOCHEMISTRY OF A P‐FLUOROPHENYLALANINE‐RESISTANT CELL LINE OF ACER PSEUDOPLATANUS L.
Authors: GATHERCOLE R. W. E. , STREET H. E.
Published: May 2006

Cell lines resistant to growth inhibition by 10 μM DL‐p‐fluorophenylalanine (PFP) have been isolated from a stock cell suspension culture line of Acer pseudoplatarms L. One of the lines (X8) retained its resistance when serially subcultured in the absence of PFP. X8 could not be distinguished from the parent line in growth rate and biomass yield but in mixed cultures of the two lines, X8 cells progressively declined as a fraction of the cell population during serial subculture in the absence of PFP. The X8 line could be recovered from such mixed cultures by subculture to medium containing 10 μ(M PFP. Line X8 resembled the parent cell line in phenyl‐alanine (PA) pool size and in showing no evidence of discrimination between PA and PFP in protein synthesis. It differed from the parent line in exhibiting lower uptake of PFP and PA; at an appropriate level PA almost completely suppressed PFP uptake. X8 cells had a higher content of phenols and higher extractable activity of phenylalanine ammonia lyase (PAL); they actively degraded absorbed PFP. The problem of isolation of biochemical mutants from plant cell cultures is discussed.
CHEMICAL MODELS FOR PLANT WAX MORPHOGENESIS
Authors: CHAMBERS T. C. , RITCHIE I. M. , BOOTH MARGARET A.
Published: May 2006

Evidence from recrystallization and surface diffusion studies is presented which suggests that the patterns of leaf cuticular wax deposits are mainly a function of the wax chemical composition. Wax probably arrives at the cuticular surface in a solvent which subsequently evaporates. Surface diffusion across the cuticle is not believed to contribute significantly to the wax growth process. Most of the compounds which comprise the wax, form plates or sheet‐like structures when crystallized from solution. In eucalypt leaf waxes, the naturally occurring plate waxes appear to be associated with the polar constituents of the wax. Natural waxes which occur as tubes probably contain a mixture of non‐polar compounds.