bluuebunny/crossref_metadata_2025_split huggingface dataset:
CUTICLE STRUCTURE AND WATER RELATIONS OF THE NEEDLES OF PINUS RADIATA (D. DON)
Authors: LEYTON L. , ARMITAGE I. P. 
Published: May 2006

SummaryThe fine structure of the cuticle of mature needles of Pinus radiata has been studied from electron micrographs of carbon replicas of the needle surface. The whole of the needle surface appears to be covered by a layer of wax from which, with the exception of the inner surface normally enclosed by the sheath, arise numerous tubular waxy outgrowths similar to those previously observed in P. sylvestris. Unlike P. sylvestris, these outgrowths cover only a portion of the exposed needle surface and the underlying wax layer ranges in appearance from smooth to slightly granular, with no indication of a plate‐like structure.When the needles were immersed in water, very little was taken up into the basal region of the needles normally enclosed by the sheath compared with the exposed surfaces; the tips of the needles showed the highest permeability to water. The inner surfaces of the needles were consistently more wettable than the outer surfaces, and the surfaces normally enclosed by the basal sheath, corresponding to the youngest regions of the needle, were much less wettable than the exposed surfaces. The inner enclosed surface was the least wettable of all; this may be due to differences in the chemical composition of the wax, besides the absence of weathering.When young needles were prematurely exposed by removing the basal sheath, tubular, waxy outgrowths appeared, similar to those found on the exposed surfaces of the mature needles; when young needles were bound together to prevent them from parting, an entirely different structure developed consisting of minute granules forming a reticulum over the surface.The significance of the above findings is discussed in relation to the reputed relatively high cuticular transpiration of P. radiata and its ability to absorb water directly into the foliage from precipitation; it appears that this species is well adapted to the moist atmospheric conditions characteristic of its native habitat in the Californian ‘fog belt’ region.
INTROGRESSIVE HYBRIDIZATION BETWEEN BETULA NANA L. AND B. PUBESCENS EHRH. IN NORTH‐WEST ICELAND
Authors: ELKINGTON T. T. 
Published: May 2006

SummaryIn Iceland the genus Betula is represented by B. nana L., which has little morphological variation, and a variable series of shrub and tree birches. A comparison of these variable populations in the Skjaldfannardalur area, Isafjardardjup, north‐west Iceland with British populations of B. pubescens Ehrh. (2n= 56) and B. nana (2n= 28) using histograms of hybrid indices has been made and it is concluded that the variation is due to introgressive hybridization between B. pubescens and B. nana. The introgressed B. pubescens populations have a lower fertility than those of B. nana.The mechanism of gene flow is discussed and it is suggested that it is more likely to be either direct from diploid to tetraploid levels or via intermediate triploids rather than through the formation of aneuploid complexes.
AN ULTRASTRUCTURAL STUDY OF SEXUAL REPRODUCTION IN PYTHIUM ULTIMUM
Authors: MARCHANT R. 
Published: May 2006

SummaryThe original observations of sexual reproduction in Pythium ultimum have been re‐interpreted in the light of electron microscope observations. The antheridium of P. ultimum penetrates the oogonium with only a slight constriction of the antheridium and not through a tube as described previously. During the development of the oospore the amount of storage material increases and the wall thickens. In the mature oospore there is a single centrally placed nucleus and most of the rest of the oospore is filled with storage material. The few remaining organelles are found in small pockets between the storage organelles. The lenticular body, originally described as the nucleus, appears to be an artifact produced from the periplasm.
STUDIES IN DACTYLIS
Authors: PARKER P. F. , BORRILL M. 
Published: May 2006

SummaryHybridizations were carried out between samples of ten diploid Dactylis subspecies. Both pollen fertility and ‘fertility index’ of hybrids decreased from initial cross to F2. There was no correlation of fertility with geographical distribution of the parents, and despite the fall in hybrid fertility it was considered that gene exchange would not be completely prevented.
FLOWERING CYCLES AND FRUIT TYPES OF FICUS SYCOMORUS IN ISRAEL
Authors: GALIL J. , EISIKOWITCH D. 
Published: May 2006

SummaryFlowering cycles in the ‘Balami’ variety of Ficus sycomorus, the sycomore, were studied in connection with the sycophilous wasps Sycophaga sycomori and Apocrypta longitarsus. In the coastal plain of Israel the syconia of Ficus sycomorus may follow either of two developmental courses: most of the syconia swell rapidly, when still at an early stage of anthesis, thus producing genuinely ‘vegetative parthenocarpic’ fruit; some of them, however, become inhabited by Svcophaga sycomori and then follow a full developmental course, ultimately producing ‘stimulative parthenocarpic’ fruit. The latter type of fruit is seedless, as is the former, and the stimulus for its development is provided by the wasps ovipositing in the flower ovaries and by the subsequent activity of the wasp larvae within. In order to ascertain the reason for the absence of seeds, controlled pollination experiments were conducted. These experiments, and also systematic observations on the sequence of flowering generations throughout the year, have yielded information on seed‐setting and the interrelations between the sycomore and its wasps.
BEHAVIOUR OF BOMBUS ON DIGITALIS SPP.
Authors: PERCIVAL M. S. , MORGAN P. , LEWIS D. E. 
Published: May 2006

SummaryThe behaviour of Bombus agrurum, B. lucorum, B. pratensis, B. terrestris and B. lapidarius in exploiting the flowers of Digitalis purpurea, D. amandiana, D. mertouensis, D. ambigua and D. lanata is described, and the reasons for their ‘preferential foraging’ explained, in part, as a function of the physical difficulties of the workers in entering the flowers.
RANDOMNESS IN THE GENESIS OF PHYLLOTAXIS
Authors: RIJVEN A. H. G. C. 
Published: May 2006

SummaryA survey of a number of species belonging to the Trifolieae has revealed that the first leaf in the mature embryo may occupy one of two positions, designated ‘inside’ and ‘outside’. Fourteen species exhibited an equal frequency distribution between the two classes, ten showed a bias towards an inside position, and two a bias towards an outside position. Complete determination was only encountered in other tribes of the Leguminosae.In Trtgonella foenum‐graecum L. the chance factor in the determmation of first leaf position acted independently in two adjacent ovules of a pod. Experiments demonstrated that the degree of inside bias of T. foenum‐graecum could be influenced by nutritional and temperature treatments but not by light treatments. Supplementing plant cultures with manganese chloride solutions increased the bias, but calcium nitrate decreased the bias. Lower temperatures decreased the bias, and abolished it when plants were cultured at 15° C (day)/10° C (night).Bias is an expression of genotype in offspring. By line breeding from two parent plants for three generations a hereditary component to the variability in bias could be shown to exist.In Medicago rugosa Desr., which has an outside bias, manganese chloride as compared with calcium nitrate treatment favoured the inside position.The view is advanced that the determination of a major morphological axis may come about as a consequence of random disturbances in a Turing type process.
ELECTRON MICROSCOPIC STUDY OF ASEXUAL SPORES IN KICKXELLACEAE
Authors: YOUNG T. W. K. 
Published: May 2006

SummaryInvestigation of the surface structure of spores in Kickxellaceae by means of electron and phase contrast microscopy has revealed the presence of spinous protuberances in all the species investigated except Coemansia reversa. Spore spines are clearly nippled in some species and are arranged in various ways. From the evidence presented it appears that in several species the spore is liberated from within the merosporangial membrane thus behaving in a similar way to most other members of Mucorales.
CRASSULACEAN ACID METABOLISM UNDER NATURAL TROPICAL CONDITIONS
Authors: MILBURN T. R. , PEARSON D. J. , NDEGWE N. A. 
Published: May 2006

SummaryThe content of various metabolic intermediates has been determined in material from several species of succulent plants known to show a Crassulacean acid metabolism, grown under natural conditions at Kampala, Uganda. Free titratable acidity, malate, citrate and isocitrate, present in considerable amounts, and various keto‐acids present in relatively small amounts, have been measured both at dawn and during the later afternoon. In the case of leaf from two species of Bryophyllum natural changes of keto‐acid content were followed in detail.Overnight changes in free titratable acidity could, in all cases, be largely attributed to malate accumulation, but citrate also increased considerably in some species. Diurnal fluctuations in isocitrate were not observed. Concentrations of both oxaloacetate and α‐oxo‐glutarate increased markedly overnight. In the two Bryophyllum species, pyruvate concentrations were maximal during photodeacidification. The phosphopyruvate content of B. crenatum leaf increased slightly during photodeacidification but was low during dark acidification. No isocitrate lactone was detected in B. calycinum leaf.Observed oxygen uptake rates would account for the complete oxidation during photodeacidification of only a small proportion of the malate decarboxylation product. Probable pathways involved in the formation and utilization of malate are discussed.
HALOPHYTES, SUCCULENCE AND SODIUM IN PLANTS—A UNIFIED THEORY
Authors: JENNINGS D. H. 
Published: May 2006

SummaryReference to the relevant literature shows that sodium ions can bring about increased succulence and, with regard to their response to sodium, halophytes differ from mesophytes only in degree, not in kind. Attention is drawn to the fact that the effect of sodium parallels the effect of increased light and aridity. It is proposed that these three factors exert the same effect on plant cells, namely to bring about an increased ATP synthesis. The mechanism whereby sodium ions bring this about is thought to be due to the reversal of a membrane‐bound ATPase which can otherwise act as a sodium pump. Aridity brings about increased concentration of sodium ions in the xylem sap and light brings about increased ATP synthesis via photophosphorylation. It is pointed out that the cell membranes must possess certain other physiological properties, if sodium is to act in the manner described. Attention is drawn to the fact that such an action of sodium ions would provide a homeostatic mechanism whereby the plant cell could avoid the detrimental effect of high concentrations of toxic ions.
A COMPARATIVE STUDY OF BICARBONATE INHIBITION OF ROOT GROWTH IN CALCICOLE AND CALCIFUGE GRASSES
Authors: LEE J. A. , WOOLHOUSE H. W. 
Published: May 2006

SummaryA study has been made of the effects of bicarbonate on the root growth of a number of calcicole and calcifuge grasses. Differential effects of bicarbonate concentrations likely to be encountered in a calcareous soil solution (0–10 m‐equiv./litre) were found between the species. In general the root growth of calcifuge species was more strongly inhibited than was the root growth of calcicoles. Using the technique of colchicine‐induced metaphase accumulation the mitotic index of the roots of the bicarbonate‐inhibited calcifuge Deschampsia flexuosa was measured and the effects of bicarbonate were then studied. No effect of bicarbonate on cell division was detected and it was concluded that the inhibitory effect of bicarbonate was mainly on cell elongation. Using H14CO3 it was found that the maximum rates of dark‐fixation occur in those zones of cell elongation where the main inhibition of growth takes place.
ACTION SPECTRA FOR PHOTOSYNTHESIS AND LIGHT‐STIMULATED ION TRANSPORT PROCESSES IN HYDRODICTYON AFRICANUM
Authors: RAVEN J. A. 
Published: May 2006

SummaryThe action spectra in the wavelength range 436–759 nm of photosynthesis and light‐dependent ion transport processes in Hydrodictyon africanum were determined. The action spectra for active Cl influx and the associated components of K and Na influx, and the passive K efflux and the passive component of K influx, all had action spectra very similar to that of photosynthesis. These processes are stimulated by light absorbed by the photosynthetic system, and require photosystem 2. Active K influx and the coupled Na efflux, on the other hand, do not show such a pronounced drop in the action spectrum above 680 nm as does photosynthesis; below 680 nm the action spectrum is very similar to that of photosynthesis. This cation regulation mechanism thus only needs photosystem I. The results obtained above 680 nm confirm and extend those previously obtained with cut‐off filters (Raven, 1967b).The Emerson enhancement effect was exhibited by photosynthesis but not by Cl influx. The absence of enhancement of Cl influx could not be explained by a de‐enhancing action of photochrome at the wavelengths used. This absence of enhancement, if genuine, implies that only photosystem 2 is needed for light‐stimulation of Cl influx.No evidence was found for participation of the blue pigment or of phytochrome in any of the processes studied.
STOMATAL RESPONSES TO LIGHT AND CARBON DIOXIDE IN THE HART'S‐TONGUE FERN, PHYLLITIS SCOLOPENDRIUM NEWM.
Authors: MANSFIELD T. A. , WILLMER C. M. 
Published: May 2006

SummaryThe stomata of Phyllitis scolopendrium differ from those of angiosperms in that the guard cells contain many chloroplasts, comparable in size and appearance with those of the mesophyll. Experiments are described showing that the stomata of this fern respond to light and darkness and changes in carbon dioxide concentration in the same way as those of angiosperms. The stomata opened widely in conditions in which there could be no net photosynthetic carbon dioxide fixation, and it is therefore concluded that substances produced from carbon dioxide by photosynthesis do not play a major role in the opening mechanism and possibly no direct role at all.
AGE‐GOVERNED RESPONSES OF DETACHED TOMATO LEAVES TO PHYTOKININS
Authors: McHALE JANIECE S. , DOVE LEWIS D. 
Published: May 2006

SummaryYoung tomato leaves differed from older leaves in their response to phytokinin treatment after leaf detachment. N,6‐benzyladenine kept old leaves at a ribonuclease (RNase) activity level similar to that of freshly harvested material while controls increased in RNase activity. RNase activity of younger leaves was not suppressed until after a longer period of detachment but the initial post‐harvest treatment induced this effect. Young leaves treated with kinetin at first had a higher RNase activity level than controls but RNase activity in controls had increased by 8 days after detachment while activity in kinetin‐treated tissue remained near the level observed 4 days after detachment. Early response in young leaves to phytokinins was interpreted as slightly toxic, reminiscent of the more toxic response of attached leaves to phytokinins. Loss of greenness was delayed by phytokinin in both young and old leaves but RNase activity was affected first. Young leaves detached from water‐stressed plants showed an early response to N,6‐benzyl‐adenine which was similar to that obtained from older leaves after detachment. Water‐stress altered an age‐governed response to phytokinin. Phytokinins probably did not directly inhibit RNase activity, increase destruction of the enzyme, or preserve membrane‐bound bodies containing the enzyme. It is suggested that phytokinins affect RNase synthesis directly and that this phase of leaf senescence is more fundamental to the life of the cells than mobilization phenomena.
ANALYTICAL STUDIES OF THE GROWTH OF THE ETIOLATED SEEDLINGS OF AVENA SATIVA
Authors: SABNIS HEATHER , MER C. L. 
Published: May 2006

SummaryEtiolated Avena seedlings have been treated with phosphates (P) and light (L) in a factorially arranged experiment. P increased the growth of the mesocotyls by maintaining cell division in the nodal meristem; cell length was not affected. While L inhibited cell division irrespective of the presence of P, a differential effect on cell growth was observed. Without P some few cells remained short after having been illuminated, but no such cells were seen in the plants given P. This difference can be correlated with cell length at the time of illumination. The inhibitory effect of L on mitosis can be disassociated from that on cell growth.
ADENOSINE TRIPHOSPHATE CONCENTRATION IN RELATION TO RESPIRATION AND RESISTANCE TO INFECTION IN TISSUES INFECTED BY VIRUS
Authors: BAYLEY JILL , MERRETT M. J. 
Published: May 2006

SummaryWhen leaves of Nicotiana tabacum L. var. Xanthi were infected with tobacco etch virus, local lesion formation was accompanied by an increased rate of respiration which coincided with an increase in their adenosine triphosphate concentration. Stimulation of respiration by 2.4 dinitrophenol decreased to a low value with increasing lesion density. A combination of increased adenosine triphosphate concentration and greater adenosine triphosphate turnover may contribute towards the increased respiration of the local lesion host. Adenine greatly increased the adenosine triphosphate concentration of healthy leaves but not the respiration rate. With the local lesion leaf, where adenosine triphosphate concentration was increased by virus infection, adenosine triphosphate concentration was unaffected by adenine. Treatment of leaves with adenine increases resistance to virus infection, while healthy tissue surrounding virus‐induced local lesions is also resistant to reinfection; both give increased adenosine triphosphate concentration suggesting that this is an important factor in resistance to virus infection. Increased adenosine triphosphate concentration in the leaf may result in the production of additional host ribonucleic acid which then occupies receptor sites usually available to virus ribonucleic acid.
PHYSIOLOGICAL ACTION OF THE GERMINATION INHIBITOR IN THE HUSK OF AEGILOPS KOTSCHYI BOISS
Authors: WURZBURGER JUDITH , LESHEM Y. 
Published: May 2006

SummaryThe germination inhibitor contained in the glume and hull of Aegilops kotschyi, an Irano‐Turanian graminaceous species growing in Israel, was investigated. It appears to function via the gibberellin (GA) metabolism of the plant and is coumarin‐ or abscisin‐like in action.
LATE WEICHSELIAN AND FLANDRIAN POLLEN DIAGRAMS FROM SOUTH‐WEST SCOTLAND
Authors: MOAR N. T. 
Published: May 2006

SummaryThe history of Late Weichselian and Flandrian vegetation in south‐west Scotland has been studied by examining sites ranging from near sea‐level up to about 1500 ft O.D. (c. 500 m). Pollen was scarce or absent in Lower Dryas sediments, but the relatively high counts in Allerod sediments implied that an open herbaceous vegetation was established before this time. Throughout the Late Weichselian the vegetation was an herbaceous one which became more stable and denser during the Allerod, but was much reduced during Upper Dryas time. Early Flandrian vegetation remained open and the spread of birch woodland was delayed for some time. Once established the birch forests remained dominant or co‐dominant for a long period and were never completely replaced by mixed‐oak forest. Because of the differences in vegetation development it was difficult to correlate significant changes in the pollen curves with the standard British system of pollen zones. For this reason an attempt has been made to devise a system of zones appropriate for Scotland which bears comparison with the presently accepted scheme. Apparent breaks in sedimentation at Bigholm Burn and Culhorn Mains, only revealed by pollen analysis, are treated as local phenomena, the causes of which had no effect upon the character of the regional vegetation. Radiocarbon assay of samples from Bigholm Burn show that the ages of Allerod sediments are consistent with those from other parts of Britain, but early and mid‐Flandrian dates are considerably younger than their biostratigraphical equivalents elsewhere. Until more dates are available from the region this apparent anomaly is regarded as being an effect of local factors influencing forest development and sedimentation. Although the distribution of sites about the Southern Uplands implies that glaciers were restricted to higher altitudes the present study does not add significantly to our knowledge of the extent of glaciation in this region during the Late Weichselian.
ON THE DETERMINATION OF LEAF FORM IN RANUNCULUS AQUATILIS
Authors: COOK C. D. K. 
Published: May 2006

Summary Ranunculus aquatilis L. is an amphibious plant that shows a spectacular kind of heterophylly; the leaf primordia possess the genetic competence to develop three different kinds of leaf: i, the submerged divided leaf which is made up of long, cylindrical, capillary segments; 2, the terrestrial divided leaf which is made up of short, flattened, capillary segments; and 3, the entire leaf which has a normal expanded blade borne on a petiole. An account is given of the structure and development of these leaf forms. The effects of temperature, photoperiod, light intensity and emergence or submergence in water on the determination of leaf form were studied. Temperature and light intensity unless exceptionally high or low played no role in the determination of these leaf forms. It was found that the submerged divided kind of leaf was developed in terrestrial or submerged conditions under short photoperiods (10 hours or less) but under long photoperiods (14 hours or more) it developed only on submerged stems. The terrestrial divided leaf was formed only under long photoperiods in terrestrial conditions while the entire kind of leaf, which occupies the air‐water interface, was developed only under long photoperiods in submerged conditions. Photoperiod, therefore, determines the epigenetic ability of the stem apex to develop different kinds of leaf but it is the presence or absence of water per se that regulates the phenotypic expression of this epigenetic ability. The ecological and evolutionary significance of this kind of leaf form determination are discussed.
THE FINE STRUCTURE OF WALL MODIFICATIONS AND ASSOCIATED STRUCTURES IN CALLUS TISSUE OF ANDROGRAPHIS PANICULATA NEES.
Authors: BOWES B. G. 
Published: May 2006

SummaryIn established callus cultures of Andrographis paniculata grown on a solidified nutrient medium, numerous spherical multivesiculate bodies, c. 0.6–3 μ in diameter, are visible. These usually contain membrane‐bounded vesicles and tubules of up to 0.2 μ diameter enclosed within one to several membranous lamellae, but myelin‐like forms also oeeur. The origin of sueh multivesiculate bodies is uncertain but the Golgi apparatus or endoplasmie reticulum may be implicated. The multivesiculate bodies apparently f'use to the cell wall to form lomasomes and these organelles deposit their membranous contents into the wall and give rise to membranous wall bodies. These bodies eontain a plethora of membrane‐bounded vesicles, or membrane segments which may be isolated or associated in myelin‐like configurations. The vesicles probably contain precursor materials utilized in the synthesis of the fibrillar material in which the membranous inclusions in the wall are embedded. Associated with the membranous wall bodies, numerous wall invaginations develop in seneseing tissue and divide the cells into progressively smaller compartments. The latter eventually become almost completely occluded, apparently due to the secretion of fibrillar material into their lumens by multivesiculate bodies and membranous wall bodies.