bluuebunny/crossref_metadata_2025_split huggingface dataset:
STOMATAL BEHAVIOUR FOLLOWING TREATMENT WITH AUXIN‐LIKE SUBSTANCES AND PHENYLMERCURIC ACETATE
Authors: MANSFIELD T. A. 
Published: May 2006

SummaryThe ‘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

SummaryMorphological 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

SummaryThis 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

SummaryFor 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

SummaryThe 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

SummaryThe 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

SummaryRelationships 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

SummaryCells 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

SummaryA 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

SummaryThe 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

SummaryRibonuclease (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

SummaryThe 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.
LABIATAE: TAXONOMY AND SUSCEPTIBILITY TO PUCCINIA MENTHAE PERS.
Authors: EL‐GAZZAR A. , WATSON L. 
Published: May 2006

SummaryCorrelations 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

SummaryThe 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

SummaryAn 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

SummaryThere 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

SummaryAngiospermic 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

SummarySharp 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

SummaryAn 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

SummaryEstimation 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

SummaryIn 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

SummaryConjugating 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.