bluuebunny/crossref_metadata_2025 huggingface dataset:
FLOWERING CYCLES AND FRUIT TYPES OF FICUS SYCOMORUS IN ISRAEL
Authors: GALIL J. , EISIKOWITCH D.
Published: May 2006

Summary

Flowering 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

Summary

The 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

Summary

A 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

Summary

Investigation 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

Summary

The 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

Summary

Reference 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

Summary

A 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

Summary

The 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

Summary

The 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

Summary

Young 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

Summary

Etiolated 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

Summary

When 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

Summary

The 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

Summary

The 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

Summary

In 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.
EFFECTS OF HERBICIDES ON THE GROWTH OF SOIL FUNGI
Authors: WILKINSON VALERIE , LUCAS R. L.
Published: May 2006

Summary

Three methods have been used to investigate the effects of a number of commercial herbicides on the growth of certain soil fungi: measurements of hyphal extension across agar plates; measurements of hyphal extension along sterilized plant material; and manometric techniques. Three points, in particular, emerged from these studies. First, that there was no stimulation of fungal growth. Herbicide interference in growth included suppression of spore germination, inhibition of the rate of linear extension of the mycelia, and abnormalities in growth habit and in patterns of spore production. Secondly, that some herbicides (e.g. linuron and paraquat) were more fungitoxic than others (e.g. MCPA and simazine) to a range of organisms. Thirdly, that there were differences between fungi in their sensitivity to individual herbicides. All three methods have shown consistent differences between fungi in their ability to tolerate paraquat. Trichoderma viride, in particular, has been found to be sensitive to paraquat. The inhibitory effects were observed at concentrations well within the range likely to be experienced in the field.
CELLULOSE AS A CARBON SOURCE FOR ORCHID MYCORRHIZA
Authors: HADLEY G.
Published: May 2006

Summary

Orchid endophyte fungi are known to utilize cellulose and translocate carbon compounds into protocorms. Evidence is presented which indicates that cellulose is an excellent carbon source for protocorm growth in a variety of orchid‐fungus systems including both temperate and tropical orchids. One per cent cellulose powder as compared with 1% dextrose as a carbon source enhanced the development of protocorms and led to a more sparse, controlled growth of the fungal endophyte and, subsequently, a diminished tendency to parasitism and death of the protocorms. It is not yet known whether cellulose is equally useful for root‐bearing mature orchids but it may be the principal carbon source in nature for orchids in the symbiotic protocorm stage.
THE PHOSPHORUS METABOLISM OF RHIZOPUS STOLONIFER AND CHAETOMIUM SP. WITH RESPECT TO PHOSPHORUS TRANSLOCATION
Authors: LYON A. J. E. , LUCAS R. L.
Published: May 2006

Summary

Rhizopus stolonifer was able to translocate 32phosphorus readily through established hyphae, whereas Chaetomium sp. was unable to do so. When colonies of either species were incubated on KH232PO4 a range of compounds became labelled in the mycelium but a substantial proportion of absorbed 32P was present in the form of orthophosphate in both species. After incubating 32P‐labelled mycelium of Rhizopus stolonifer on unlabelled KH2PO4, the proportion of 32P detected in the form of orthophosphate was unchanged. When mycelium of Chaetomium sp. was treated in this way the proportion of label in the orthophosphate fraction was greatly reduced. Mycelium of Rhizopus stolonifer was able to take up hexose [32P] phosphate intact and subsequently hydrolyse it to orthophosphate. In Chaetomium sp. very little 32P derived from hexose [32P] phosphate appeared as orthophosphate.

These results are held to support the view that the ability to translocate phosphorus is associated with rapid turnover of phosphorus compounds.
THE EFFECT OF ABSCISIC ACID ON STEM ELONGATION AND CORRELATIVE INHIBITION
Authors: ARNEY S. E. , MITCHELL D. L.
Published: May 2006

Summary

The mature length of the second internode (which was undergoing rapid vacuolation at the time of treatment with ABA) was not appreciably affected by doses of ABA below 20 μg per plant although the rate of elongation was depressed for the first 2 days after treatment, the depression being as much as 50% in tall varieties. Doses of ABA in excess of 20 μg not only depressed elongation rate immediately, but resulted in shorter internode length at maturity. Etiolated seedlings showed a stimulation of elongation rate and mature length in the dwarf ‘Meteor’, hut no statistically significant differences in the tall variety ‘The Pilot’ with doses below 20 μg ABA. Higher doses of ABA caused immediate cessation of elongation in vacuolating internodes, but only postponed the onset of vacuolation in younger internodes. Lighted plants also showed this postponement of the onset of vacuolation in the younger internodes at higher doses; in both lighted and etiolated seedlings the normal growth rate was resumed after a delay of between 3 and 7 days.

Decapitation reduced elongation rate during the subsequent 48 hours either with or without ABA. In the absence of ABA there was a subsequent recovery in growth rate of the dwarf variety so that the final length of the second internode was the same for both intact and decapitated plants. But decapitation of the tall variety produced a marked reduction in mature length of the second internode, as it did in all ABA treated plants both dwarf and tall, intact and decapitated. The only significant interaction between decapitation and ABA on elongation rate occurred in the tall variety: during the first 24 hours all doses of ABA produced approximately the same big reduction in elongation rate in intact plants but had no statistically significant effect on decapitated plants; during the second day only the higher doses of ABA reduced the elongation rate of intact plants while all three levels produced the same big reduction in elongation rate of the decapitated plants. In the dwarf variety there was no significant interaction between the decapitation and ABA effects. Lateral bud outgrowth in decapitated plants was inhibited by ABA, and 100 μg per plant achieved inhibition comparable to that produced by the apex in intact plants. Hence ABA may possibly be the inhibitory substance demonstrated to be responsible for the phenomena of correlative inhibition.
EFFECTS OF GIBBERELLIC ACID ON INTERNODE GROWTH AND STARCH CONTENTS OF EUCALYPTUS CAMALDULENSIS SEEDLINGS
Authors: BACHELARD E. P.
Published: May 2006

Summary

Effects of gibberellic acid (1 and 10 μg/plant) on internode extension and cell activity in Eucalyptus camaldulensis seedlings varied with internode position. The relatively small increased extension of lower internodes resulted from cell elongation whereas the progressively increasing growth in upper internodes was caused primarily by cell division. Transverse cell divisions induced by gibberellic acid seemed to require an active apical meristem.

Changes in internode diameter growth (increased in lower internodes, decreased in upper) due to gibberellic acid were the result of changes in cell division.

The major response to gibberellic acid seems to be an increase in transverse cell divisions and does not seem to be due to competition between meristems for the available food reserves.
RESISTANCE TO WATER FLOW IN SOIL AND PLANT
Authors: ANDREWS ROSALIE E. , NEWMAN E. I.
Published: May 2006

Summary

Two experiments described in an earlier paper, on the transpiration rates of root‐pruned and unpruned wheat plants at various soil moisture contents, are discussed with the aid of further data.

The matric potential drop across the rhizosphere, and the relative magnitude of the rhizo‐sphere and plant resistances are calculated for the unpruned plants at various soil matric potentials. Even at −15 bars soil matric potential the estimated drop was only 0.02 bar, and the rhizosphere resistance was less than 2% of the plant resistance.

The amount of water made available to the plant by root extension was only a small fraction of that lost by transpiration. We suggest that root interception is unlikely to be important in the field, as long as new roots are growing among existing ones.

Reasons are considered for the declining influence of root pruning on transpiration as the soil dried. It can be partly explained by the soil resistance remaining very small and by the relationship between transpiration rate and leaf water potential. However, there was evidently some other factor involved, possibly change in plant resistance or influence of root kinins on transpiration rate. The effects of root pruning on transpiration are too complex to provide satisfactory evidence on the magnitude of the rhizosphere resistance, but the experimental results are at any rate in agreement with the calculated prediction that it remained very small.
EFFECT OF LIGHT INTENSITY DURING GROWTH ON LEAF ANATOMY AND SUBSEQUENT LIGHT‐SATURATED PHOTOSYNTHESIS AMONG CONTRASTING LOLIUM GENOTYPES
Authors: WILSON D. , COOPER J. P.
Published: May 2006

Summary

The effect of light intensity during leaf formation on subsequent light‐saturated photosynthesis and its relation to mesophyll and stomatal characteristics, was examined among ten contrasting Lolium genotypes. Photosynthetic activity was recorded at three CO2 concentrations. At approximately 300 ppm CO2 and above, plants of the same mesophyll cell size grown in strong light (0.130 cal/cm2/min) of radiation in the spectral region 400–720 mμ. (1800 ft‐candles) had faster rates of photosynthesis than those grown in relatively weak light (0.021 or 0.056 cal/cm2/ min). At the lowest CO2 concentration there was no effect on photosynthesis of the light intensity at which the plants were grown. The effect of light intensity was not associated with any change in mesophyll structure, but plants grown in weaker light (0.056 cal/cm2/min) had much smaller stomata than those grown in stronger light (0.130 cal/cm2/min). A slight increase in stomatal frequency at the low compared with the high light intensity did not compensate for the reduced stomatal length in terms of total pore space. Differences in apparent photosynthesis in any one light intensity, and between plants from all light intensities at the lowest CO2 concentration, were usually correlated negatively with mesophyll cell size. Effects of the light intensity at which plants were grown on subsequent photosynthesis could be explained in terms of changes in stomatal size.
THE FLORAL BIOLOGY OF THREE SPECIES OF VIOLA
Authors: BEATTIE A. J.
Published: May 2006

Summary

The floral biology of Viola riviniana Rchb., V. reichenhachiana Jord. and V. hirta L. is described in detail. The flowers are very complicated morphologically and many changes in the floral organs occur during anthesis. Differences in the flowering periods of the three species were found but comparisons of the length of flower life, the pollen and nectar presentation and the receptivity of the stigmatic surfaces showed few differences between species. Movements of the pedicel and corolla directly affect the outline and colour patterns presented by the flower and these are probably of prime importance in the attraction of insect visitors to these species. All the movements of the floral organs and the changes which they undergo together suggest that anthesis has two distinct phases. The first is characterized by the retention of pollen within the androecium and the second is characterized by the gradual displacement of pollen from the anthers to the petals. Pollination during the flrst phase is effected only by a few insect species which operate the pollination mechanism precisely. By contrast, pollination during the second phase may be effected by a wide variety of insect visitors and is not, therefore, entirely dependent upon the activities of a small number of highly adapted species, as previously supposed. This may be of critial importance to the many species of Viola which are predominantly in‐breeders. In the absence of highly adapted pollinators (which is frequently the case), the second phase of anthesis may be the only opportunity for out‐breeding. The frequency of pollen exchange in the three species is, therefore, partially dependent upon the change in the mode of pollen presentation during anthesis.
SOME ASPECTS OF THE DEVELOPMENT OF MANGO (MANGIFERA INDICA L.) LEAVES
Authors: TAYLOR F. J.
Published: May 2006

Summary

The mango is an example of a tree in which all the leaves on a shoot develop simultaneously instead of sequentially. The growth in area of all the leaves in a flush was followed at daily intervals. The dry weight, ash weight, water content, relative turgidity and rigidity of the leaves were measured at weekly intervals for the first 6 weeks of their life. They grew by cell division for the first 7 days after the fall of the bud scales and by cell enlargement over the next 7 days. Between day 7 and day 14 the dry weight per unit leaf area fell, the water content per unit leaf area increased, and the leaf became less rigid, finally hanging limply. After this date these trends were reversed. It is shown that the limpness of the young mature leaves is not due to lack of turgor, but may be correlated with a minimal value of the dry weight per unit leaf area.
THE EFFECT OF NITROGEN SUPPLY ON SOME INDICES OF PLANT‐WATER RELATIONS OF BEANS (PHASEOLUS VULGARIS L.) *
Authors: SHIMSHI DANIEL
Published: May 2006

Summary

The effect of nitrogen supply on some indices of plant‐water relations was studied on potted bean plants. When soil moisture was relatively high, the leaves of N‐deficient plants transpired less than those of N‐supplied plants, the transpiration rate being closely associated with the chlorophyll content of the leaves of various ages. In detached leaves which were saturated by floating over distilled water, stomatal width was markedly wider in N‐supplied than in N‐deficient plants. Throughout the available moisture range, the water saturation deficit was higher in N‐supplied leaves. In the dry range of soil moisture, chlorotic leaves transpired more than normal green leaves; N‐deficient plants failed to exhibit a sharp rise in the content of soluble metabolites in the sap, when approaching the wilting range. The content of ‘cell wall materials’ was higher in N‐deficient plants. The relationships between these indices is discussed; it is tentatively concluded that nitrogen deficiency impairs the ability of the plants to adjust their water status to changes in soil moisture by regulation of stomatal transpiration and of sap‐solute concentration.
CONTRIBUTIONS TO THE ECOLOGY OF BRACKEN (PTERIDIUM AQUILINUM)
Authors: WATT A. S.
Published: May 2006

Summary

The variation in height and density of the fronds in the hinterland of area D is confirmed as stages in the development of bracken from the pioneer to the mature phase. Factors affecting its rate are winter and spring frost and rainfall. In the absence of interference there would appear to be no degenerate phase such as has been described as part of a natural cycle of change in the hinterland of area E.

By the use of thatch and cage development is expedited but later reactions ensue affecting the number of fronds, their height, spindliness and depth of origin such as are found in the degenerate phase in area E. Thatch and cage induce degeneration in area D and probably accentuate it in area E.

The mechanism of degeneration requires detailed investigation but it would appear to involve the change from a community (mature phase) in area D where the old shoots are dispersed singly or at most in small groups in an uneven‐aged population to one in which they are aggregated in larger more or less even‐aged patches such as are found in area E.

In the contrast between the hinterlands of area D and area E as well as in phasic development, litter, its amount and kind, emerges as important. Burning removes this litter and its influence on bracken in different phases, leading in some to retrogression and even local extinction, in others to rejuvenation, is discussed.
SOME ECONOMIC IMPLICATIONS OF THE TAXONOMY OF LABIATAE ESSENTIAL OILS AND RUSTS
Authors: EL‐GAZZAR A. , WATSON L.
Published: May 2006

Summary

Essential oils extracted from twenty‐two genera of Labiatae have been examined by gas‐liquid chromatography. The results support the taxonomic suggestion that there are two major series of genera: the one (GROUP B, El‐Gazzar & Watson 1970) oil‐rich, the other appearing to be oil‐poor. Records of susceptibility to Puccinia menthae Pers. are nearly confined to the oil‐rich group, but within this assemblage certain minor groupings of important genera may be resistant. Attention is drawn to commercial possibilities among large GROUP B genera (e.g. Hyptis, Plectranthus; as yet exploited hardly or not at all) known to be oil‐rich and possibly resistant to Rusts including Puccinia menthae.
ABSORPTION OF POLYETHYLENE GLYCOLS BY PLANTS AND THEIR EFFECTS ON PLANT GROWTH
Authors: LAWLOR D. W.
Published: May 2006

Summary

A study was made of polyethylene glycols (PEG) as osmotica to decrease the water potential of culture solutions for studies of higher plant response to water stress. Analysis of possible inorganic impurities in commercial PEG and comparison of the growth of maize in solutions purified by gel filtration or unpurified, suggest that impurities are not responsible for the toxic effects reported.

PEG in leaves was estimated by Hyden's method and with [14C]‐labelled PEG 4000. Over 90 % of the higher molecular weight PEG was recovered from maize and bean leaves but less from cotton and tulip tree. PEG of 1000 molecular weight or larger entered plants slowly, about 1 mg/g fresh weight of leaf per week, but mechanically damaged roots or those subjected to low water potentials permitted entry. PEG decreased transpiration and water potential and caused the leaves to die. PEG 200 and mannitol entered plants with undamaged roots but the effects on leaves were unlike the higher molecular weight PEGs.

Low and high molecular weight PEG and mannitol affected respiration to the same extent and comparison with non‐ionic detergents showed that the detergent properties of PEG were not responsible for the toxicity.

Autoradiography showed that PEG 4000 accumulated initially in the margins of leaves and became distributed in the mesophyll except along the veins.

PEG of higher molecular weight is considered to cause blockage of the pathway of water movement, reducing water absorption and causing desiccation of the plant.
FURTHER OBSERVATIONS OF CATION‐STIMULATED STOMATAL OPENING IN ISOLATED EPIDERMIS
Authors: WILLMER C. M. , MANSFIELD T. A.
Published: May 2006

Summary

Measurements of apparent osmotic pressures of guard cells in isolated epidermis of Commelina communis indicate a considerable rise (up to 26.3 bars) when K+ ions are added to the incubation medium. This rise in apparent osmotic pressure appears to be the major cause of the stomatal opening that is stimulated by K+ ions, but reduction in turgor of the epidermal cells, owing to the solutes in the incubation medium, may also contribute to the wide stomatal apertures. Histochemical tests on epidermis taken from leaves with stomata that were closed in darkness, or that were open in light, suggest that K+ accumulates in guard cells when stomata open in response to light. No movements of K+ or Na+ from epidermis to mesophyll could be detected and it is concluded that ion movements associated with changes in guard cell turgor are probably confined to the epidermis in C. communis. Ion uptake (indicated by 86Rb and 24Na) into epidermis was stimulated by light but not by a reduction in CO2 concentration, whereas stomatal apertures were affected by these environmental factors to approximately the same extent. It is tentatively concluded that active transport of monovalent cations into guard cells might explain the CO2‐independent light responses of stomata, but not their light‐independent CO2 responses.
EFFECTS OF SIMULATED DROUGHT ON SHOOT DEVELOPMENT IN LIRIODENDRON SEEDLINGS
Authors: DOLEY D.
Published: May 2006

Summary

Shoot extension, leaf growth, xylem radial growth, and xylem structure in i‐year old Liriodendron tulipifera L. seedlings maintained in a growth chamber were affected more by reduction of atmospheric relative humidity from about 95 to about 45% than by simultaneous reduction of the root medium water potential (Ψsoi) from – 0.4 to about –11 bars. For plants subjected to the same minimum Ψsol, the rate of change of Ψsol during the imposition and relief of simulated drought had no apparent effect on growth. Xylem formed near the stem base during a period of simulated drought resembled that characteristic of the terminal stage of seasonal growth under normal conditions; vessel elements, fibres and ray parenchyma cells were narrower in the radial direction, vascular rays increased in width, and more vertical parenchyma was evident than under conditions of rapid growth. The differences between the structure of xylem formed at high and low plant water potentials diminished towards the apex of the stem, and it is suggested that these differences may be due chiefly to an impairment of synthesis and translocation of growth factors.
CHANGE OF APPARENT WEIGHT OF PLANT TISSUES IN SOLUTIONS
Authors: BRIGGS G. E.
Published: May 2006

Summary

The effect of changes in the vacuole of the amounts of solute and of water, and of the turgor pressure, on the apparent weight of a cell and of a piece of tissue is considered. The permeability of cells in the root of carrot is estimated from the change in apparent weight of discs suspended in a solution of KNO3. The permeability to urea is estimated from the change in apparent weight in water after discs had equilibrated with a solution of urea. The dimensions of permeability to water and solute, and the effect of flow of water on the apparent permeability to solute, are considered. The change in apparent weight is used to measure the relatively slow uptake of cane sugar from dilute solutions of this substance. The uptake is not due to passive diffusion and the sugar absorbed appears to be osmotically active. From measurements of carbon dioxide produced and chloride ions absorbed from 0.01 M KC1 the change in apparent weight in water and change in osmotic pressure of the vacuolar sap are estimated. These are compared with the observed changes in apparent weight and changes in osmotic pressure deduced from the change in the relation between the vacuolar volume and the concentration of KC1 with which it is in equilibrium.
THE SUBCELLUAR DISTRIBUTION OF ZINC AND COPPER WITHIN THE ROOTS OF METAL‐TOLERANT CLONES OF AGROSTIS TENUIS SIBTH.
Authors: TURNER R. G.
Published: May 2006

Summary

Heavy metal tolerance in the common bent grass Agrostis tennis Sibth. was investigated by comparing the zinc and copper distribution within the roots of metal‐tolerant and non‐tolerant clones. Analysis of root subcellular fractions showed the importance of the cell wall fraction in metal binding in root cells of metal‐tolerant A. tenuis. At normal nutrient levels the root cell wall from metal‐tolerant clones contained more copper and zinc than did non‐tolerant material. High levels of metal nutrition demonstrated the accumulating power of this fraction. Alterations in the nutrient level of one heavy metal did not influence the distribution of the other metal studied. The importance of metal accumulation by the cell wall fraction is discussed and it is proposed that it is an important site in the mechanism of heavy metal tolerance in A. tenuis.
THE MORPHOLOGY OF VEGETATIVE REGENERATION IN CALLUNA VULGARIS
Authors: MOHAMED B. F. , GIMINGHAM C. H.
Published: May 2006

Summary

Calluna vulgaris, in certain habitats, provides useful grazing for herbivores; management is generally by burning, with the aim of promoting vigorous production of young shoots by vegetative regeneration for the stem base. However, the capacity for such vegetative regeneration declines with age. The general morphology of the plant is described, with particular reference to the sequence of development in a single season's growth and to the stages in resumption of growth after overwintering. On this basis, an interpretation is given of the responses to grazing and burning, with evidence derived from detailed observation of treated plants and from transverse sections of stems. Light grazing at the periphery of the plant causes (i) the growth of a few of the uppermost short shoots into new long shoots, and (ii) the appearance of clusters of shoots from lower, woody, parts of the branches. Heavier or more sustained grazing emphasizes the second of these responses. Vegetative regeneration after burning is also of the second category, confined to undamaged positions near the base of the stem.

The clusters of shoots appear at the points of origin of existing or former branches. The conclusion, derived both from morphological observations and from evidence of the deep‐seated origin of these new shoots, is that they are derived from persisting dormant buds on the close‐packed nodes just below the base of each long shoot. These nodes belonged to the overwintering end‐of‐season short shoot from which the long shoot developed.
AGEING IN PLANT EMBRYOS
Authors: BERJAK PATRICIA , VILLIERS T. A.
Published: May 2006

Summary

Although no cell division was detected in the radicle during the first 24 hours of imbibition by the caryopses of Zea mays, fine structural changes showed the re‐establishment of a developmental pattern during this period. Such changes included mitochondrial differentiation, the appearance of dictyosomes and a complex system of ER, and the association of ribosomes to form polysome‐like structures. Association between ER and lysosome‐like bodies was seen during this stage, together with an intensification of the acid phosphatase reaction within the lysosomes. By the 48‐hour stage, easily‐separated, senescent cells had been produced and cell division had begun. Vesicles produced by the hypersecretory activity of the dictyosomes were either incorporated into the developing lysosomes or passed through the cell membrane to the wall. In the outermost cells the lysosomes finally ruptured and acid phosphatase activity became detectable in the ground cytoplasm. The development of the lysosomes and the hypersecretory activity of the dictyosomes are discussed as evidence of constructive changes implying genetic control of cellular senescence in the root cap.
EFFECTS OF SOME METABOLIC INHIBITORS AND TEMPERATURE ON ION‐STIMULATED STOMATAL OPENING IN DETACHED EPIDERMIS
Authors: WILLMER C. M. , MANSFIELD T. A.
Published: May 2006

Summary

Ion‐stimulated stomatal opening in isolated epidermis of Commelina commons is shown to be influenced by temperature in the manner expected for a process dependent on metabolism. The effects of three metabolic inhibitors on this stomatal opening in light and darkness and two concentrations of CO2 are reported. 3‐(3,4‐dichlorophenyl),I,I‐dimethylurea (DCMU) caused partial stomatal closure in light but this was reversed in CO2‐free conditions, suggesting that open chain photophosphorylation is not essential for stomatal opening in light. Salicylaldoxime suppressed the light‐stimulated component of stomatal opening and the effect was not reversed in CO2‐free conditions. This suggests that photosystem 1 or cyclic photophosphorylation supplied the energy for ion uptake in guard cells in light. Supporting evidence comes from the finding that 2,4‐dinitrophenol (DNP) also suppressed the light‐stimulated component of opening.

In darkness, ion‐stimulated opening occurs, but to smaller apertures than in the light. This opening is insensitive to DNP treatment, suggesting that ATP from oxidative phosphorylation is not required. A possible interpretation of the results is that in darkness the energy for active transport into the guard cells is obtained from a direct linkage to the mitochondrial electron transport chain; the same could be true in light, with an additional linkage to electron transport in photosystem I. Lack of information on the movement of specific ions means that some doubt must remain about which ions are actively transported. A comparison of the behaviour of stomata on detached and attached epidermis suggests that care is required if data from this study are to be applied to the stomatal mechanism in intact Plants.
THE NATURE OF SEED DORMANCY AND GERMINATION IN THE SALT MARSH GRASS DISTICHLIS SPICATA
Authors: AMEN RALPH D. , CARTER GEORGE E. , KELLY RICHARD J.
Published: May 2006

Summary

Distichlis spicata, a salt marsh grass, sets dormant seeds which exhibit a low‐temperature, after‐ripening requirement. In addition to stratification, localized scarification and nitrate are effective agents in breaking dormancy and promoting seed germination. The pericarp and/or testa are impermeable to organic plant‐growth regulators, but not to water or inorganic salts. Gibberellic acid and kinetin are ineffective in breaking dormancy and do not affect germination. Abscisic acid, however, effectively inhibits stratified and scarified seeds. Dormancy and germination appear to be hormonally controlled.

It is suggested that the endogenous inhibitor constitutes a block to nitrate reductase activity in the endosperm. Presumably the inhibitor blocks specific DNA transcription sites in the aleurone cells, but can be overcome by after‐ripening (inhibitor decay), abrasion (inhibitor leaching) or nitrate induction.