bluuebunny/crossref_metadata_2025 huggingface dataset:
COMPARATIVE BIOLOGY OF TUSSILAGO FARFARA L., CHAMAFNERION ANGUSTIFOLIUM (L.) SCOP., EPILOBIUM MONTANUM L. AND FPILOBIUM ADFNOCAULON HAUSSKN.
Authors: MYERSCOUGH P. J. , WHITEHEAD F. H.
Published: May 2006

Summary

The four species investigated occur in pioneer habitats but have different distributions. This study of their comparative biology is an attempt to account for these differences.

The literature on the factors determining habitats and geographical distribution of each species is reviewed but this gives little or no evidence as to whether the species are causally related to, or merely associated with these factors in their ecological distribution. Experiments were therefore designed to test the causal relationship and mode of action of the factors, and this first paper describes those dealing with germination.

It appeared from the literature that factors of probable importance in determining the ecological distributions of the species include mineral nutrients and light requirements. The mineral nutritional requirements of Chamaenerion angustifolium seemed to be particularly high. Tussilago farfara appeared to be the most calcicole and Chamaenerion angustifolium the most calcifuge of the species. Epilobium montanum seemed to be the most shade‐tolerant. Additional factors appeared likely to be involved at the limits of their geographical distributions; these include, along the southern limits, factors operating through the water relations of the species, and along the northern limits factors operating through the temperature relations and length of season of growth of the species.

The wind‐dispersed seeds of the species are of low dry weight. Water culture experiments showed that, with regard to germination, Tussilago farfara is most successful and Chamaenerion angustifolium least successful in very low levels of mineral nutrient supply. The germination of Tussilago farfara in relation to increasing acidity is completely inhibited at a bigher pH (3.5) than it is in the other species (pH 3.0). In T. farfara germination is also restricted to the period mid‐April to mid‐June by the limited length of its seed viability and season of fruit dispersal. In the other species, though seed shedding is restricted to summer and autumn, the seed remains viable for at least a year and requires light to germinate. In Chamaenerion angustifolium this light requirement disappears as the temperature is raised to 30°C, but it remains in the two Epilobium species. At low temperatures (10°C) maximal percentage germination occurs under lower levels of illumination in E. adenocaulon than it does in Chamaenerion angustifolium, and this probably underlies the much greater percentage germination attained in Epilobium adenocaulon than in Chamaenerion angustifolium when the seeds are shallowly buried (2 mm). Germination in dry conditions also occurs more readily in Epilobium adenocaulon than in Chamaenerion angustifolium. Epilobium montanum is most similar to E. adenocaulon in germination requirements but differs in that its germination is inhibited at 30°C.
VI. PRELIMINARY STUDIES OF PHOTOSYNTHESIS AND CARBOHYDRATE METABOLISM OF THE LICHEN XANTHORIA AUREOLA
Authors: BEDNAR T. W. , SMITH D. C.
Published: May 2006

Summary

Most of the carbon fixed in photosynthesis by Xanthoria aureola (X. parietina var. aureola) initially accumulates in sugar alcohols and relatively little is incorporated into insoluble compounds at first. Two kinds of sugar alcohol are involved—mannitol and a pentitol. During the early stages of photosynthesis, much more carbon accumulates in the pentitol than in mannitol. Within 9–15 minutes of exposure to NaH14CO3 in the hght, the level of 14C in metabolic intermediates presumably common to both symbionts (PGA, hexose monophosphates, organic acids) became more or less steady and remained so for several hours. It was concluded from this that it is likely that the flow of carbon from alga to fungus is relatively rapid and efficient, and achieved a steady rate within 15 minutes of the start of the experiment.
A METHOD OF MAINTAINING FRACTIONS OF FIELD CAPACITY IN POT EXPERIMENTS
Authors: WHITEHEAD F. H. , HOOD J. S. R.
Published: May 2006

Summary

Difficulties in the maintenance of fractions of field capacity in pot experiments by existing methods are discussed. A new technique, only applicable at present to artificial soils, is described. It consists of blowing saturated air through the soil maintained at an appropriate temperature difference until the required field capacity is achieved. Results obtained are described briefly.
THE CUTICLE OF THE LEPIDODENDROID STEM
Authors: THOMAS B. A.
Published: May 2006

Summary

The value of the cuticle in the study of the stems of Carboniferous arborescent lycopods is discussed. The cuticle gives information about the stomata (which are very numerous suggesting that the tissues beneath were vigorously photosynthetic), it is sometimes of value in demonstrating the presence of a ligule pit where this is concealed, and it helps understanding of how the cortex enlarged in certain species. The cuticle may also be of value in elucidating taxonomic relationships between various stems.
THE USE OF EPIDERMAL CHARACTERS IN PHYLOGENETIC CONSIDERATIONS
Authors: STACE C. A.
Published: May 2006

Summary

In order to ascertain the phylogenetic significance associated with leaf epidermal characters eight genera of mangroves in the families Combretaceae, Rhizophoraceae and Avicenniaceae were compared with each other and with non‐mangrove genera of the same families. The mangrove genera share a number of common features, but are easily separated into three groups coinciding with the three families. Further differences, of successively lesser order, enable all eight genera and some of the species within them to be distinguished. With regard to epidermal characters the mangroves of any one family show closer resemblance to the non‐mangroves of the same family than to mangroves of other families. Differentiation by epidermal characters thus closely parallels that by characters more usually used in plant taxonomy.
EFFECT OFENDOGONEMYCORRHIZA ON PLANT GROWTH
Authors: DAFT M. J. , NICOLSON T. H.
Published: May 2006

Summary

The growth effects of three mycorrhizalEndogoneendophytes on tobacco, tomato and maize were examined. The extent of the stimulus obtained depended on nutrient conditions and the subsequent level of infection developed in the root system. Marked stimulation occurred with low phosphate availability and high root infection.
ABSORPTION OF NITROGEN BY MYCORRHIZAL ROOTS OF BEECH
Authors: CARRODUS B. B.
Published: May 2006

Summary

Beech mycorrhizas are capable of absorbing ammonia and simple organic compounds from solution but nitrate is a poor source of nitrogen if it is absorbed at all. The absorption of ammonia is associated with synthesis of organic nitrogen compounds in the tissues amongst which glutamine appears as the most prominent. The factors which affect absorption are those expected to affect metabolic activity. The rate of ammonia absorption is stimulated especially at certain times of year by exogenous sugars applied during or immediately before ammonia absorption. Prefeeding with either glucose or fructose stimulates absorption and so it may be concluded that trehalose, glycogen and mannitol may all be utilized in the process. Low concentrations of bicarbonate, up to 7·5 mM, enhance ammonia absorption as do succinic, fumaric and malic acids. Other organic acids applied exogenously either do not affect uptake or reduce its rate.
THE EFFECT OF BICARBONATE ON THE UPTAKE OF IRON IN FOUR RELATED GRASSES
Authors: WOOLHOUSE H. W.
Published: May 2006

Summary

A sodium bicarbonate concentration of 20 m‐equiv./l brought about a partial inhibition of uptake of 59Fe by intact roots of Deschampsia flexuosa; subsequent translocation of the 59Fe to the shoots was also inhibited. A similar concentration of bicarbonate produced no inhibition of uptake by the related grasses Holcus mollis, Arrhenatherum elatius and Koeleria cristata. The amount of 59Fe translocated to the shoots in the course of the experiment was less than 1% of the amount of isotope which became associated with roots. Whilst the high uptake by the roots is suggestive of some absorption on the root surface there is evidence also of uptake, probably into a substantial pool of free iron within the root.
EFFECTS OF GIBBERELLIC ACID ON GROWTH, TUBER FORMATION AND CARBOHYDRATE DISTRIBUTION IN SOLANUM TUBEROSUM
Authors: LOVELL P. H. , BOOTH A.
Published: May 2006

Summary

Two series of experiments have been described. In the first, plants treated with gibberellic acid (GA), together with untreated controls, were harvested at intervals from the time of planting and the growth of shoots, stolons and tubers measured and the dry weight and sugar and starch values determined. Treatment with GA enhanced both shoot and stolon growth and dry weight, but delayed tuber initiation. The appearance of starch correlated closely with tuber Initiation in both treated and untreated plants, but there was no correlation between sugar level in the stolons and their tuberization. In the second, 14CO2 was fed to single leaves of plants in which tuber initiation had just commenced. In untreated plants, almost all the translocated 14C accumulated in the tubers, in plants pre‐treated with GA a few days earlier, practically no 14C was detected in the stolons or tubers, but accumulated in the shoot, particularly at the apices. There were significant differences in the relative amounts of 14C in the ethanol‐soluble and ethanol‐insoluble fractions in the two treatments. The pattern of translocation shown is held to reflect the activity of the various metabolic sinks, the activity of these sinks being hormonally controlled.
FOLIAR SENESCENCE IN PERILLA FRUTESCEXS (L.) BRITT
Authors: HARDWICK K. , WOOLHOUSE H. W.
Published: May 2006

Summary

Data are presented from analyses of the changes in dry weight, chlorophyll, protein and RNA content of the third pair of leaves of Perilla frutescens from the time of completion of leaf expansion to abscission. It is shown that the amounts of these leaf constituents change at different rates and that the changes occur at different rates in different parts of a leaf.
THE ULTRASTRUCTURAL BASIS OF HYPHAL GROWTH
Authors: MARCHANT R. , PEAT A. , BANBURY G. H.
Published: May 2006

Summary

Two vesicular systems associated with wall synthesis have been observed in Phycomyces blakesleeanus, Fusarium culmorum and Coprinus lagopus; these fungi have chitin in their walls. A system of vesicles produced by the endoplasmic reticulum is believed to be responsible for ‘primary’ wall synthesis. These vesicles fuse with the plasmalemma. Multi‐vesicular bodies from which lomasomes are formed are also produced by the endoplasmic reticulum; these are seemingly associated with ‘secondary’ wall synthesis, and it is suggested that they may be concerned with chitin deposition in the wall. Pythium ultimum, which has non‐chitinous walls, lacks multi‐vesicular bodies. Structures which have some features in common with lomasomes are present in Coprinus lagopus and Pythium ultimum, but they are postulated to arise by elaboration of the plasmalemma.
PERFECT STATES OF RHIZOCTONIAS ASSOCIATED WITH ORCHIDS
Authors: WARCUP J. H. , TALBOT P. H. B.
Published: May 2006

Summary

Rhizoctoma isolates obtained from terrestrial orchids in South Australia and Great Britain have been induced to fruit in culture. The perfect states thus obtained belong to Thanatephorus cucumeris (Frank) Donk, T. sterigmaticus (Bourdot) Talbot, T. orchidicola Warcup and Talbot, Ceratobasidiinn cornigerum (Bourdot) Rogers, C. obscurum Rogers, Ceratobasidium sp. indet., Tulasnella calospora (Boudier) Juel, T. asymmetrica sp. nov., Tulasnella sp. indet. and Sebacina lermifera Oberwinkler. Tulasnelta calospora was found to be the perfect state of three cultures considered to be Rhizoctonia repens Bernard. The status of the orchid‐fungus association is discussed.
THE EFFECT OF THE LEAF ON DIFFERENTIATION OF PRIMARY XYLEM IN THE INTERNODE OF COLEUS BLUMEI BENTH.
Authors: WANGERMANN ELISABETH
Published: May 2006

Summary

If a very young leaf blade of Coleus bluinei Benth. is excised, the differentiation of primary xylem in the traces belonging to the treated leaf virtually ceases and all the cells in that half of the internode below the leaf are reduced in size. If the excised blade is replaced by auxin paste, differentiation of xylem proceeds almost normally and cell size is restored. Autoradiographs of sections of internodes treated apically with radioactive auxin paste indicate that after trans‐location auxin is heavily concentrated in the vascular bundles.
COMPARATIVE BIOLOGY OF TUSSILAGO FARFARA L., CHAMAFNFRION ANGUSTIFOLIUM (L.) SCOP., EPILOBIUM MONTANUM L., AND FPILOBIUM ADFNOCAULON HAUSSKN.
Authors: MYERSCOUGH P. J. , WHITEHEAD F. H.
Published: May 2006

Summary

This paper describes the results of experiments on the growth of Tussilago farfara, Chamaenerion angustifolium, Epilobium montanum and E. adenocaulon in glasshouse conditions and also results of field experiments with Chamaenerion angustifolium and Epilobium adenocaulon. These results and results of work on germination, reported in the previous paper of this series, are discussed in relation to the ecology of the species.

Glasshouse experiments showed that the growth forms of Epilobium montanum and E. adenocaulon are under the control of daylength but the growth form of Chamaenerion angustifolium is not controlled by it. All four species were found to make adequate growth under a range of shade conditions and nutrient supply. In all four species, plasticity of form of adaptative significance was shown to occur with respect to both light and mineral nutrient supply.

Certain attributes of the species appear to be of high significance in determining, under natural selection, their ecological distributions. These include the longevity of dormant seed and the efficiency of dormancy mechanisms. Differences in these between the species appear to lead to differences in their occurrence in deciduous woodland and in their occurrence as weeds of cultivated ground.

The small seed size of the species together with their commitments to large amounts of seedling growth relative to seed weight, operate to restrict seedling establishment to open sites in which supplies of light and mineral nutrients are adequate. The growth commitments of C angustifolium appear to be appreciably larger than in the other species and in C. angustifolium seedling establishment was found to be restricted by the nutritional status of certain experimental sites to a greater extent than in Epilobium adenocaulon.

Differences between the species in growth form and pattern of vegetative reproduction appear, in part, to account for the differences in their occurrence in sites with mobile soil surfaces and in closed communities.

The species differ in capacity for germination and viable growth on acid substrates. Also, between the species there are differences in their growth in regimes of high calcium/low potassium concentrations. Both these differences are considered to be of importance in determining respective differences of distribution of the species on acid and on lime‐rich soils.

Finally, some assessment is made of the relative importance of genetic diversity and phenotypic plasticity to the survival of the species in the wide ranges of habitats in which they occur. The importance of differences in breeding system in maintaining different levels of diversity in the species is discussed.
STUDIES IN SEED DORMANCY
Authors: BRADBEER J. W. , COLMAN B.
Published: May 2006

Summary

The dormancy of hazel seeds (Kent cob nuts) has been found to be broken by less than 30 days chilling at 5° C. During 50 days chilling there was no detectable growth of the embryonic axes although growth rapidly commenced when the temperature of 50‐day chilled seeds was raised to 20° C.

Both cotyledon slices and embryonic axes from dormant seeds showed active metabolism of [2‐14C] acetate, the operation of the following enzymes and enzyme systems being inferred: TCA cycle, glutamate dehydrogenase, aspartate aminotransferase and those involved in the syntheses of lipid, protein, sucrose, DNA and RNA. As no evidence has been found of the appearance of further metabolic pathways during chilling it is suggested that the block to the germination of dormant seeds may be in the partial blockage of a metabolic pathway. Quantitative changes in the distribution of [2‐14C]acetate label, which occurred during chilling, have been interpreted as indicative of a fall in the lipid synthesizing ability of cotyledons and a rise in the aspartate, glutamate and protein synthesizing ability of the embryonic axes. The embryonic axes also appeared to develop increased TCA cycle activity and showed increased sucrose labelling. However, none of these changes appeared to occur at as early a stage of the chilling process as the change in nucleotide metabolism previously reported.
STUDIES IN SEED DORMANCY
Authors: WOOD A. , BRADBEER J. W.
Published: May 2006

Summary

The nucleic acids of the cotyledons of hazel (Corylus avellana L.) seeds have been extracted by a modified phenol method and subsequently fractionated on a methylated serum albumin‐kieselguhr (MAK) column. Fractions which appear to contain soluble RNA (sRNA), ribosomal RNA (rRNA) and messenger RNA (mRNA) have been found in addition to one which contains both DNA and RNA (DNA‐RNA).

During the first 10 days after imbibition there was little nucleic acid synthesis in seeds kept at either 4° C or 20° C. However, changes in the sRNA appear to have occurred at both temperatures and the formation of additional sRNA from other nucleic acid molecules has also been inferred. It is suggested that imbibition may result in the activation of a postulated stable and inactive form of sRNA occurring in the dry seed. Imbibition also induced the appearance of the light and heavy fractions of rRNA. After 10 days at 4° C 20 % of the seeds were able to germinate at 20° C. Further chilling caused a substantial fall in seed dormancy together with considerable nucleic acid synthesis. It would appear that nucleic acid synthesis does not play a part early in the process of breaking hazel seed dormancy by chilling, but it is possible that it plays a part at a later stage of the process.

Seeds, chilled at 4° C for 50 days and then transferred to 20° C for 5 days showed an apparently large increase in the rate of cotyledonary nucleic acid metabolism. A net fall in the content of rRNA and DNA‐RNA was also found.
THE DIFFERENTIATION AND FATE OF THE BRACKEN (PTERIDIUM AQUILINUM) FROND AND THEIR RELATION TO THE AGE‐STRUCTURE OF THE SHOOT AND FROND POPULATION
Authors: WATT A. S.
Published: May 2006

Summary

On an acid, dry infertile soil in a frost pocket, there are more short shoots (potential fronds) in bracken than differentiated fronds, and more differentiated fronds than emerge from the soil, and more emergent fronds than live in August.

Factors affecting the inception, differentiation and fate of fronds are examined. The inherent tendency of fronds from young shoots to develop and to emerge before those from old renders them more liable to lethal winter and spring frosts and to crippling spring frosts. Drought acts mainly on the late emerging fronds. The normal sequence of emergence may be upset.

Through their destruction of reserves and their effect on the means of replenishing them, annually fluctuating frost and drought influence the number of shoots initiated yearly, and hence the age‐structure of the shoot population. A senescent population of bracken is defined as one in which the proportion of young to old shoots is low, and fronds from young shoots to fronds from old is also low. Frost and drought are the causes (not necessarily exclusive) of senescence in this area.
NOTE ON THE DETERMINATION OF LEAF WATER‐POTENTIAL
Authors: TINKLIN R.
Published: May 2006

Summary

A simplified modification of the micro‐osmometer of Macklon and Weatherley (1965a) for the determination of depressions of water‐potential in leaves, ΔW (DPD), is described.

The apparent minimum ΔW of 31/2 atm for non‐transpiring water‐culture plants of Ricinus communis reported by Tinklin and Weatherley (1966) is considered further. Evidence is provided that this is in fact a zero value, the level recorded being due to the errors induced by water loss on sampling and by water uptake by continued growth of tissue during determinations. However, a simple subtraction of 31/2 atm from all ΔW values is not proposed as there are indications that a threshold AH’may exist above which continued growth does not occur, so that higher ΔW records will approach more closely the true value.
STUDIES IN THE GERMINATION AND ESTABLISHMENT OF JUNCUS SQUARROSUS
Authors: WELCH D.
Published: May 2006

Summary

Observations and experiments on the germination and establishment of Juncus squarrosus are described. Germination is confined to seeds lying on the ground surface and normally occurs in the spring. It was shown experimentally that germination can occur on a variety of media, including a calcareous soil, but that the germination percentages were reduced on dry soils. Complete germination of viable seeds occurred in 13 days in suitable conditions (frequent watering, 12 hours of light per day, and a room temperature of 23° C), but the rate was lower when less light and lower temperatures were given. At 14° C, germination did not occur in darkness and it would appear that light is either necessary for germination at this temperature, or raises the temperature of the medium surface sufficiently for germination to occur. Upland winter conditions had no effect on the viability of the seeds.

Development of both root and shoot is very slow and evidence is presented that lack of competitive ability is the reason for the infrequency of successful establishment of seedlings. Colonization on blanket peat was found to be encouraged by lime and fertilizer treatments, but very few seedlings became established unless competition from Calluna, Eriophorum or a sown grass was reduced.
RECOVERY FROM DORMANCY IN ROOTS
Authors: CLOWES F. A. L. , STEWART HELEN E.
Published: May 2006

Summary

Seedlings of Zea mays have been grown at 5° C to induce dormancy in their root apices. Recovery has been studied when the plants were returned to 21° C by observing the changes in cell patterns, in the labelling of nuclei with [6‐3H]thymidine and in rates of mitosis measured by metaphase accumulation. Recovery involves stimulation into division of the cells of the quiescent centre and the consequent repopulation of other regions of the meristem from the quiescent centre. We suggest that the reason for this behaviour is that the quiescent centre cells are less badly injured during the cold because their nuclei, which are normally at G1, rest there. By contrast, in the surrounding meristem, many of the cells being at S or G2 at the onset of cold, proceed through mitosis to the following G1 and, in so doing, suffer chromosomal damage and impairment of reproductive potential. This view is supported by the hypersensitivity found in the cap initials, which normally have no G1 phase. Some previous work on dormancy and on the organization of meristems is discussed in the light of this theory.
A NOTE ON SUCROSE AND GLUCOSE UPTAKE BY APICAL SEGMENTS OF TOMATO ROOTS
Authors: THOMAS D. R. , WEIR N. R.
Published: May 2006

Summary

Accumulation and uptake of sugars from glucose and sucrose by apical segments of excised tomato roots were compared. Greater uptake and accumulation occurred from sucrose which may, in part, contribute to the characteristically better growth of the roots in sucrose.
STOMATAL BEHAVIOUR FOLLOWING TREATMENT WITH AUXIN‐LIKE SUBSTANCES AND PHENYLMERCURIC ACETATE
Authors: MANSFIELD T. A.
Published: May 2006

Summary

The ‘synthetic auxins’2‐naphthoxyacetic acid (NOXA), i‐napththylacetic acid (NAA) and 2,4‐dichlorophenoxyacetic acid (2,4‐D) caused stomatal closure when apphed to detached leaves via their petioles. In the case of NOXA and NAA this closure was readily reversed if the intercellular spaces were flushed with CO2‐free air, but the closure due to 2,4‐D was not reversed by such treatment. It is concluded that NOXA and NAA cause stomatal closure by disturbing the CO2 balance in the leaf (by stimulating respiration or inhibiting photosynthesis) whereas 2,4‐D exerts a more direct effect on the guard cells.

Phenylmercuric acetate (PMA) caused stomatal closure on strips of detached epidermis, and this could be prevented by CO2‐free air during the first 2 hours of treatment. Subsequently closure did occur in CO2‐free air but by this time the toxicity of PMA had apparently led to death of the cells. The relevance of these observations to the idea that chloroplast volume changes participate in the stomatal mechanism is discussed.
OBSERVATIONS ON NATURAL CLONES IN HOLCUS MOLLIS
Authors: HARBERD D. J.
Published: May 2006

Summary

Morphological examination of a group of fifty‐eight isolates of Holcus mollis from natural hill vegetation suggested that the collection was composed of four plant‐types only. Further experiments proved that there were major discontinuities between the plant‐types, and relatively little heterogeneity within them. It is argued that each plant‐type corresponds to a single colonizing seedling. Acceptance of this interpretation implies that natural stands of H. mollis contain very few genotypes, some of them replicated very many times, and this fits in with the presumed cytological history of the species. One of the genotypes observed was found in an area over half a mile across, in an ecological non‐uniform terrain, so that the actual migration route might have been much longer.
PHYSIOLOGICAL EFFECTS OF MICRONUTRIENT DEFICIENCIES IN ISOLATED ROOTS OF LYCOPERSICUM ESCULENTUM
Authors: ABBOTT A. J.
Published: May 2006

Summary

This paper describes techniques for the removal of trace element impurities in nutrient reagents without the introduction of toxic residues inhibitory to the growth of excised tomato roots. The zinc requirement of excised roots, hitherto in some doubt, is clearly demonstrated in media treated with dithizone. The three features of growth—main axis extension, lateral initiation and lateral extension—were followed during the onset of, and recovery from, iron, manganese, copper, zinc and molybdenum deficiencies. Symptoms of iron and manganese deficiencies were manifested in the first culture passage; those of copper, zinc and molybdenum in the second passage. In manganese, copper, zinc and molybdenum deficiencies, there was a gradual decline in growth rate, but growth ceased abruptly in iron deficiency. Inhibition of lateral root initiation was more severe in iron and copper deficiencies than in other deficiencies studied. Lateral elongation was stimulated by zinc deficiency and retarded less by manganese than by iron, copper and molybdenum deficiencies. Addition of deficient elements showed that primary and secondary meristems varied in their capacity to recover. Stimulation of lateral initiation occurred when iron and zinc were added to deficient cultures and lateral elongation was stimulated in manganese recovery experiments. Protracted periods in iron, manganese, copper and zinc deficient media caused degeneration of root tissues, but recovery was still possible in roots maintained without molybdenum for 28 days. Results are discussed in relation to possible predominant roles for the five trace elements in determining the pattern of growth of excised tomato roots. Response to these elements was not uniform in the root and it is clear that cellular differentiation is an important factor in trace element requirement and control of growth.
ULTRASTRUCTURE, PROTOPLASMIC STREAMING, GROWTH AND TROPISMS OF PHYCOMYCES SPORANGIOPHORES
Authors: PEAT A. , BANBURY G. H.
Published: May 2006

Summary

For a satisfactory explanation of the growth, protoplasmic streaming, and photo‐ and geo‐tropic responses of Phycomyces sporangiophores, information is needed concerning the ultrastructure of these coenocytic hyphae. The form and spatial distribution of vacuoles, and of the photoreceptors, are crucial to the analysis of phototropism. The ultrastructural basis of protoplasmic streaming and its bearing on the differential growth responses that produce tropisms need to be established, and so does a physical basis for geo‐perception. This paper describes the general ultrastructure of the growing zone of stage I and stage IVb sporangiophores viewed in transverse and longitudinal sections.

Numerous small vacuoles are present in the upper part of the growth zone, and a large central vacuole extends to within I mm of the apex. The form and distribution of vesicles believed to he involved in wall growth, and of the nuclei and mitochondria, are described. Bundles of vesicles or coiled tubules of endoplasmic reticulum showing inter‐bundle spacing comparable to that of the separate strands of the multi‐striate streaming protoplasm are reported.
TAXONOMIC IMPLICATIONS OF A COMPARATIVE ANATOMICAL STUDY OF EPACRIDACEAE
Authors: WATSON L.
Published: May 2006

Summary

The accepted arrangement of the genera of Epacridaceae rests solely on ovary and fruit characters. Observations on fibre patterns in the leaves correlate intelligibly with features of nodal anatomy, pith structure, stomatal morphology and stomatal distribution to suggest that it fails to do justice to the taxonomic diversity of the plants concerned. A study of these features, taking account of the rest of the available evidence, indicates that the family includes four major groups, only one of which (the tribe Styphelieae) is recognized in the present system. Representatives of the other three are the genera Epacris, Cosmelia and Richea. There is nothing to recommend maintaining the tribe Prionoteae. Three genera (Wittsteinia, Oligarrhena and Needhamiella) are so distinct from other Epacridaceae as to seem worthy of monogeneric tribes.
THE PRODUCTION OF AUXIN BY TOBACCO INTERNODE TISSUES
Authors: SHELDRAKE A. R. , NORTHCOTE D. H.
Published: May 2006

Summary

The formation of callus at the basal end of tobacco internode tissues cultured on a basic medium has been used as an indication of the presence of auxin within the tissues. It has been shown in this way that sections of internode are capable of producing auxin. This production of auxin is related to the continued activity of the vascular cambium. If cambial activity and vascular differentiation are eliminated, auxin is no longer produced. When tissues in which cambial activity and vascular differentiation are taking place are cultured on a medium containing an inhibitor of polar auxin transport, tri‐iodo benzoic acid, serried ranks of xylem tracheids are formed. It is suggested that auxin is produced as a consequence of xylem differentiation and the observations reported in this paper are interpreted in the light of this hypothesis. It is also suggested that kinins may be produced as a result of xylem and phloem differentiation, and the possibility that autolysing cells are a major source of both auxins and kinins in the plant is discussed.
STUDIES ON THE DEGRADATION OF CHLOROPHYLL a AND CAROTENOIDS IN FRESHWATERS
Authors: MOSS BRIAN
Published: May 2006

Summary

Relationships between chlorophyll a, its coloured degradation products and carotenoids have been examined in extracts of freshwater algal populations and sediments. Carotenoids are differentially preserved over chlorophyll a and its coloured derivatives in both aerobic and anaerobic situations, at both high and low light intensities, although preservation of carotenoids increases with decreasing oxygen availability. Light appears to exert a major effect on destruction of chlorophyll a and its derivatives.

Processes of pigment degradation and persistent sediment formation are discussed, and the use of sedimentary chlorophyll degradation product/carotenoid ratios as indices of lake fertility is examined.
LICHEN PHYSIOLOGY
Authors: RICHARDSON D. H. S. , SMITH D. C.
Published: May 2006

Summary

Cells of Trebouxia immediately after isolation from the thallus of Xanthoria aureola fix 14C mainly into ribitol during photosynthesis and [14C]ribitol can also be released from their cells. After a period in pure culture, proportionately much less 14C is fixed into ribitol, and very little fixed 14C is released from the cells. Although some 14C is accumulated in sucrose, it is not released from cells directly isolated from thalli, Ribitol could support the growth of the fungal symbiont in pure culture. The main carbohydrate present in the mycelium is mannitol, but when grown in ribitol, arabitol is also present. These results confirm studies with the intact thallus which had suggested that ribitol was the main form in which carbohydrate moved between the symbionts in the thallus.
GERMINATION OF THE LIGHT‐SENSITIVE SEEDS OF OCIMUM AMERICANUM LINN.
Authors: VARSHNEY C. K.
Published: May 2006

Summary

A brief light exposure is essential for the germination of dark imbibed seeds of Ocimum americanum Linn. Seeds with testa broken at the radicular end were independent of light requirement for germination. Red and far‐red light were found to affect germination in a fashion typical of other photomorphogenic reactions mediated through a phytochrome system. The stimulatory effect of light was not constant if the imbibed seeds were maintained in darkness for long periods. Imbibed seeds entered a secondary dormancy (skotodormancy) under prolonged darkness. This was relieved by cold treatment. The ecological implications of skotodormancy are discussed.
BREEDING BARRIERS IN SOME SPECIES OF SISYRINCHIUM
Authors: INGRAM RUTH
Published: May 2006

Summary

The cytology, breeding structure and relationships of several species of Sisyrinchium are discussed, particular attention being paid to the geographically separated populations of S. bermudiana found in America and Ireland. These are morphologically indentical, but in crossing with a second taxon, with which neither is in contact, they show a physiological difference which may have arisen by the selection in the American population of barriers to interbreeding with a third taxon with which the Irish population has no contact. The situation revealed, suggests a mechanism whereby a barrier to interbreeding could arise between populations or incipient species in non‐contiguous territories.
RIBONUCLEASE ACTIVITY IN TOMATO LEAVES AS RELATED TO DEVELOPMENT AND SENESCENCE
Authors: McHALE JANIECE S. , DOVE LEWIS D.
Published: May 2006

Summary

Ribonuclease (RNase) activity, greenness (reflectance) and chlorophyll content were determined for different ages of attached and detached leaves from 6 to 8 week old tomato plants. RNase activity of homogenates was correlated with a general indicator of senescence, chlorophyll loss. Young leaves were different from old leaves in their response to detachment. RNase activity increased almost linearly in older leaves, but younger leaves increased in activity to an ‘RNase plateau’ which was maintained for 2 days before a second increase in activity occurred. High light intensity, which is known to delay senescence, apparently delayed this second increase in RNase activity. Rooting of detached young leaves delayed loss of greenness and eventually returned leaves to the dark green condition and low level of RNase activity associated with attached leaves.

RNase activity increases during senescence were not attributed to dechne of inhibitors of the enzyme, or to rupture of hypothetical lysosomes. Suppression of RNase activity increases by actinomycin D suggested instead that enzyme synthesis was at least partially responsible for additional activity during senescence.
ANALYSIS OF MERISTEMATIC ACTIVITY IN THE ROOT TIP OF MELILOTUS ALBA DESR.
Authors: ALFIERI I. R. , EVERT R. F.
Published: May 2006

Summary

The promeristem of Melilotus alba Desr. consists of two more or less distinct layers of initials. The procambium and cortex are derived from one of these layers, while the root cap and epidermis have a common origin from the second. A diurnal periodicity of divisions exists in root tips of Melilotus, with maxima at 12.00 hours (noon) and 24.00 hours (midnight). Meri‐stematic activity extends from the initial region, or promeristem, through the level of maturation of the protophloem. Histochemical and autoradiographic studies of the root apices of M. alba, Medicago sativa L. and Trifolium pratense L. revealed that the roots of Melilotus lack well‐defined quiescent centres, that those of Medicago have large, clearly defined quiescent centres and that, although young Trifolium roots initially lack quiescent centres, such centres eventually develop to include all of the so‐called initial layers.
THE ORIGIN OF THE EXINE
Authors: GODWIN H.
Published: May 2006

Summary

An attempt is made to define the most useful lines of approach to the study of the pollen grain exine, having regard to the evidence available from light microscopy, genetics and recent electron microscopic studies.
LABIATAE: TAXONOMY AND SUSCEPTIBILITY TO PUCCINIA MENTHAE PERS.
Authors: EL‐GAZZAR A. , WATSON L.
Published: May 2006

Summary

Correlations among comparative observations on pollen grains, stomata and stem anatomy tor 125 genera of Labiatae suggest that the family comprises two main groups. This situation was hinted at by Bentham, but is completely obscured by the currently fashionable classification of Briquet. The rust fungus Puccinia menthae Pers. exhibits a very marked preference for members of one group (seventy recorded host species) over the other (only one host species).
FOLIAR SENESCENCE IN PERILLA FRUTESCENS (L.) BRITT.
Authors: HARDWICK K. , WOOLHOUSE H. W.
Published: May 2006

Summary

The uptake of [2‐14C]glycine by leaf discs of Perilla is shown to be a passive process which takes place primarily through the cut edges of the discs. Penetration of the label towards the centre of the discs proceeded only slowly and even after 24 hours on a radioactive solution the amount of isotope in the central region of the disc was no more than 30% of that in an equal area of the outer region. Incorporation of 14C was stimulated by light and increased temperature and partially inhibited by chloramphenicol. The total uptake of label into the discs increased markedly in the course of senescence; this factor may provide useful information concerning the change in permeability of the tissues with age but makes it difficult to draw any firm conclusions concerning the rates of protein synthesis in the course of senescence. The data obtained are discussed and serious doubts cast on the qualitative or quantitative value of many studies involving the use of leaf discs.
STOMATAL BEHAVIOUR IN RELATION TO RATES OF PHOTOSYNTHESIS AND TRANSPIRATION IN PELARGONIUM
Authors: WILLIS A. J. , BALASUBRAMANIAM S.
Published: May 2006

Summary

An experimental procedure is described by which contemporaneous assessments of leaf resistance, rates of transpiration and of carbon dioxide exchange can be made on attached leaves. The relative humidity and carbon dioxide concentration of an air stream flowing into a leaf chamber are controlled, and of the outflowing stream monitored. The effects of light intensity and of water relations of the leaf were investigated with reference to leaf resistance and rates of transpiration and photosynthesis. In Pelargonium × hortorum quick stomatal opening in response to illuminatioxi was observed in plants which were not under water stress. On illumination of darkened leaves the rates of transpiration and photosynthesis were shown to rise rapidly, bearing a relation to leaf resistance, and indicating stomatal control of these processes. Over long periods of illumination water deficits develop, leaf resistance increases and rates of transpiration and photosynthesis decline. Typical findings of the levels of leaf resistance at a range of light intensities, and the corresponding values of transpiration rate and photosynthetic rate, are given.

The overriding importance of water deficit in influencing stomatal behaviour in leaves under substantial water stress is shown in a series of experiments. When water deficits are fairly small, the stomata of leaves open in response to illumination, but more slowly than those of leaves of well‐watered plants; in leaves under water stress stomatal closure is also much accelerated on darkening. Under moderate water deficits, the stomata of leaves may open in response to light, but close again fairly quickly as the stress increases. Changes in rates of transpiration and photosynthesis parallel closely those of leaf resistance under these conditions. The effect of watering plants under water stress on leaf resistance and rates of gaseous exchange is shown in two experiments. The results indicate that watering leads to stomatal closure at first, with decreased rates of photosynthesis and transpiration, but subsequently leaf resistance diminishes and the rates increase as normal turgor relations in the leaf re‐establish. Stomatal behaviour and control of rates of transpiration and photosynthesis are discussed, and the water relations of the leaf shown to be of critical importance in this connection.
THE IDENTIFICATION OF BETULA NANA POLLEN
Authors: BIRKS H. J. B.
Published: May 2006

Summary

There are three approaches to the problem of distinguishing the pollen of Betula nana. Grain morphology is not considered a reliable criterion. Size measurements alone serve to distinguish B. nana pollen from B. tortuosa, whilst the grain diameter: pore depth ratio distinguishes B. nana from B. pubescens. Reliable separation of B. nana pollen from tree birch pollen requires both these parameters.
LOGICAL ANALYSIS AND ANGIOSPERMIC FAMILIES
Authors: ROBERTY G. E.
Published: May 2006

Summary

Angiospermic families are considered by the author as distinct evolutionary sets, directly issued by sexual segregation from the vegetative proliferation of green matter which covered Earth by the end of the Mesozoic geological period.

These family sets may, and consequently must, all be fitted to a common mathematical scheme, made of a Mendelian trinomial expansion through successive, interdependent but independent, evolutionary periods in each of which has become segregately fixed a functional character.

So all taxa are precisely located by means of a discontinuous numeration, whose gaps, substitute to missing links, measure dissimilarity between the actually existing forms.

This discontinuity can also be translated in cartesian coordinates corresponding to morphological degree of adaptative specialization (+ or −x), simplifying involution (y), recessive diversion (z).

Families then can easily be compared, for each of their evolutionary periods as well as in totality, inside the standard, mathematical or graphical, scheme in which is expressed the comparative pressure of past and present environmental conditions.
BIOSYSTEMATIC STUDIES IN THE LINUM PERENNE GROUP
Authors: OCKENDON D. J.
Published: May 2006

Summary

Sharp discontinuities in chromosome number and type of breeding system provide more satisfactory characters for classifying the members of the Linum perenne group than most of the morphological characters which have been used in the past. Pollen morphology has great taxonomic value here because it can be used to distinguish diploids from tetraploids and inbreeders from outbreeders. Of seventy European topodemes examined, fifty‐seven are diploid (2n= 18) and fourteen are tetraploid (2n= 36). The pollen grains of the diploids have three furrows and those of the tetraploids have six pores. All of the European members of the group are heterostylous and self‐sterile, except for L. leonii, which is homostylous and self‐fertile and endemic to Erance and Western Germany. Artificial hybrids between most of the European members of the group have been produced and their pollen fertilities recorded. No absolute sterility barriers have been found and the whole group is equivalent to a single coenospecies. The course of evolution in the group is considered in the light of all the available evidence.
HORMONAL CONTROL OF SEXUAL REPRODUCTION IN MUCOR MUCEDO
Authors: GOODAY G. W.
Published: May 2006

Summary

An investigation has been made of some aspects of the formation and action of a hormone extracted from mated cultures of Mucor mucedo which induces the formation of zygophores in unmated cultures. For a mated culture on nutrient agar there is a minimum age below which no hormone is produced. After this time hormone is produced so that the level in the culture remains constant. The production of hormone is controlled by the oxygen tension and it has been obtained from liquid cultures only when these are aerated by bubbling oxygen through the medium.

A possible mechanism for the interaction between the two strains leading to the production of hormone is discussed.

The hormone also stimulates carotenogenesis in unmated cultures which are responding to it.
ARGININE METABOLISM IN GERMINATING SEEDS OF SOME MEMBERS OF THE LEGUMINOSAE
Authors: JONES V. M. , BOULTER D.
Published: May 2006

Summary

Estimation of the arginine content of germinating seeds of Vicia faba, Canazalia ensiformis, Phaseolus vulgaris and Pisum sativum, showed a lowering in concentration during the first week of germination. When [14C] arginine was fed to cotyledon discs of Vicia faba, ornithine, proline, urea and carbon dioxide quickly became labelled and other amino acids became labelled after a longer period of incubation. Arginase was extracted from the V. faba and shown to be present in the roots, shoots and cotyledons during the first 6 days of germination. Urease was also extracted from V. faba and shown to have a pH optimum of 8.0 for extraction. The possible presence of an ornithine cycle is discussed.
PHOSPHATE ABSORPTION BY PLANTS FROM HABITATS OF DIFFERENT PHOSPHATE STATUS
Authors: NASSERY H. , HARLEY J. L.
Published: May 2006

Summary

In an attempt to elucidate the mechanisms involved in the differential growth response to phosphate of four ecologically distinct species, the rate of uptake and the incorporation pattern of labelled phosphate by their excised roots were investigated. No sufficiently striking or consistent difference was found in the rate of uptake or the pattern of esterification to explain their differences in response to phosphate. Calcium ions were found to stimulate uptake of phosphate by the excised roots of the four species, but neither could this effect be interpreted to explain the differential growth response to phosphate. The effect of calcium appeared to be to decrease both the permeability of, and the negative charges on, the root.
FUSION, SUBSEQUENT SWELLING AND FINAL DISSOLUTION OF THE APICAL WALLS OF THE PROGAMETANGIA OF RHIZOPUS SEXUALIS (SMITH) CALLEN: AN ELECTRON MICROSCOPE STUDY
Authors: HAWKER LILIAN E. , GOODAY MARGARET A.
Published: May 2006

Summary

Conjugating progametangia of Rhizopus sexualis rapidly enlarge and become flattened at the apical zone of contact. The walls over this zone fuse immediately, lose their separate identity and form a single plate. The fusion wall then thickens by gelatinization and swelling: there is no evidence of deposition of secondary wall material. The plasmalemmas on either side of the fusion wall become wrinkled and enclose pockets of electron transparent material along the sides adjacent to the wall. Vesicles and later lomasome‐like masses are seen in a few of these pockets. Numerous small vesicles are present in the adjacent zones of cytoplasm on either side of the wall; some may be seen attached to the plasmalemmas. The wall then thins from the centre of the plate outwards but remains in being until after the gametangia have been delimited by new septa. Cell fusion then takes place by the development at the centre of the fusion wall of a hole which enlarges rapidly until the whole of the plate is dissolved. The evidence from electron micrographs suggests that the dissolution process is entirely chemical and that both matrix and microfibrillar skeleton are dissolved enzymatically while still enclosed in the plasmalemma.