bluuebunny/crossref_metadata_2025 huggingface dataset:
GENECOLOGICAL STUDIES OF URTICA DIOICA L.
Authors: POLLARD A. J. , BRIGGS D.
Published: May 2006

Urtica dioica L. shows considerable variation in several characters, including stinging hair density. Members of a particular population found at Wicken Fen are remarkable in that they bear almost no stinging hairs, are tall, unbranched, narrow‐leaved, and late‐flowering. Experimental cultivation of samples from Wicken and a number of other populations showed that:

(i) Plants retain many of their distinctive features in cultivation.

(ii) Some of the variation is apparently heritable.

(iii) There are significant differences between and within populations and between staminate and pistillate plants.

(iv) Plants differ in their patterns of phenotypic plasticity.

The complexity of variation examined here renders infraspecific taxonomy difficult, but provides a fertile area for research on the ecological and evolutionary significance of variation in U. dioica.
NITRATE REDUCTASE ACTIVITY OF SPHAGNUM SPECIES IN THE SOUTH PENNINES
Authors: PRESS M. C. , LEE J. A.
Published: May 2006

Bulk deposition of nitrate, ammonium and organic nitrogen was greater at a South Pennine blanket peat site than at a similar, relatively unpolluted site in the Berwyn Mountains, North Wales. Sphagnum cuspidatum, transplanted from North Wales to the South Pennines, showed a rapid induction of nitrate reductase activity, which declined after 4 days. A laboratory induction experiment demonstrated a similar phenomenon on solutions containing 1 mM nitrate. In the presence of 1 mM ammonium, much less nitrate reductase activity was induced. Ammonium accumulated in both nitrate grown plants in the laboratory and in field transplants, which suggests that it may be responsible for the observed declines in enzyme activity. The results are discussed in relation to the nitrogen nutrition of blanket bog plants.
CORRELATION OF FUNGAL MORPHOLOGY AND DEVELOPMENT TO HOST GROWTH IN A GREEN ASH MYCORRHIZA
Authors: DOUDS D. D. , CHANEY W. R.
Published: May 2006

The relationship between the growth of the host, and development and morphology of a vesicular‐arbuscular mycorrhizal fungus was. studied in green ash (Fraxinus pennsylvanica Marsh.). A yearly cycle with three phases is suggested. Phase I is a period of fast shoot growth, slow root growth, rapid colonization of the root system by the mycorrhizal fungus and greater numbers of fungal arbuscles than vesicles. Phase II is a period of fast root growth and a decline in the percentage of root length infected. Phase III is characterized by senescing leaves, infection percentages increasing to a static level, and greater numbers of vesicles than arbuscles. Mycorrhizal green ash seedlings generally had greater heights, weights and root collar diameters and lower root: shoot ratios than non‐mycorrhizal seedlings.
LIGHT AND SELF‐THINNING
Authors: LONSDALE W. M. , WATKINSON A. R.
Published: May 2006

Monocultures of Lolium perenne were grown at high densities under various shade regimes to investigate the effects of shade on self‐thinning. Unshaded populations conformed to the minus 3/2 power law when dead matter was taken into account in the calculation of mean weight per plant. In a plot of live weight per plant, populations reached a common minus 3/2 line but then deflected from it.

Adherence to the minus 3/2 power law is a characteristic of shoots but not of whole plants of L. perenne. Populations increased in shoot:root ratio as they developed so that the thinning line for shoot plus root weight per plant was shallower than the thinning line for shoot weight per plant. Shoot: root ratios were generally higher in shaded than in unshaded populations. Tiller weights and numbers in experimental populations of L. perenne also conformed to the minus 3/2 power law.

Populations grown in deep shade thinned along a line of slope minus 1 when sown at ‘low’ densities but those sown at very high densities underwent an initial period of thinning along a slope of minus 3/2, followed by a switch to a slope of minus 1. Populations at intermediate levels of shade showed a decrease in the intercept of the thinning line with increasing shade but no change in gradient. A schematic diagram is presented to help explain the effects of shade on self‐thinning.
A DEMOGRAPHIC ANALYSIS OF THE LEAVES OF OPEN AND SHADE GROWN PINUS STROBUS L. AND TSUGA CANADENSIS (L.) CARR
Authors: WHITNEY GORDON G.
Published: May 2006

A demographic analysis of the rates of leaf formation and leaf death was initiated in open and shade grown Pinus strobus and Tsuga canadensis. The greater mean life expectancy of the shade grown leaves was attributed to (1) the evergreen habit and the obvious advantages of utilizing an extended growing season in the understory of a deciduous forest and (2) higher rates of photo‐oxidation in the sun. Tsuga canadensis failed to respond to more open habitats by altering its rate of leaf formation. Pinus strobus was considerably more flexible with regard to the formation of new leaves. Open grown trees were characterized by the production of large numbers of lateral branches and a relatively dense crown.
A SHEATHING MYCORRHIZA ON PISONIA GRANDIS R. BR. (NYCTAGINACEAE) WITH DEVELOPMENT OF TRANSFER CELLS RATHER THAN A HARTIG NET
Authors: ASHFORD A. E. , ALLAWAY W. G.
Published: May 2006

Ectomycorrhizas have been discovered on the root system of Pisoniagrandis R. Br. (Nyctaginaceae) collected from two islands in the Capricorn group of the Great Barrier Reef, Australia. These mycorrhizas are unusual in that the Hartig net is poorly developed but instead transfer cells develop in the epidermis and cortex of the host root. The wall labyrinth is located precisely on host wall regions abutting the fungus. It is suggested that the development of wall protuberances, with an accompanying amplification of host membrane surface area exactly in the region where transfer between the two symbionts is most likely to occur, is an alternative strategy to Hartig net formation. Pisonia grandis is usually found in locations colonized by seabirds as nesting sites and therefore rich in guano. It is unusual to find an ectomycorrhiza in such a situation, where there is a high input of organic nitrogen and phosphorus at least once a year in addition to a permanently high calcium level, and the nutritional aspects of this association deserve further study.
CHANGES IN FREE AMINO ACID AND AMIDE COMPOSITION DURING FRUIT AND SEED DEVELOPMENT OF GARDEN PEA, PISUM SATIVUM L.
Authors: MURRAY D. R.
Published: May 2006

Summary

Changes in the free amino acid and amide composition of the developing hull and component parts of the seeds of garden pea, Pisum sativum cv. Melbourne Market, have been recorded. Major differences observed in comparison with field pea include the absence of O‐acetyl homoserine as a prominent component in the hull or seedcoats and the absence of an increase in the relative proportion of asparagine in ageing seedcoats or maturing embryos. Serine was more prominent in young hulls, mature embryos and seedcoats and embryo sac liquid than in field pea, while arginine was less prominent in the maturing cotyledons and the embryo axis.
CYTOLOGICAL STUDIES IN THE GENUS SILENE L.
Authors: GHAZANFAR SHAHINA A.
Published: May 2006

Summary

Fourteen species of Silene in sections Siphonomorpha and Auriculatae were investigated cytologically and karyotypes prepared. Chromosome counts of six species are given for the first time. SAT‐chromosomes were found in S. viridiflora and S. nodulosa. S. boryi and S. vallesia were found to be tetraploids.
LEAF AND FLOWER DEMOGRAPHY OF TRIFOLIUM REPENS L.
Authors: TURKINGTON ROY
Published: May 2006

Summary

Ramets from a single individual of Trifolium repens L. were introduced into pure stands of Agrostis tenuis Sibth., Dactylis glomerata L., Lolium perenne L., Phleumpratense L. and Trifolium repens L. and into a bare soil (control) plot. At weekly intervals for 59 weeks, births and deaths of leaves and flowers, and extension of stolons were recorded. These birth and death statistics were used to calculate life spans, natality and mortality rates, age class distributions and other demographic characteristics of the population of leaves and flowers of T. repens L. Recruitment and death of leaves occurred throughout most of the year; flowers were produced from mid‐March to late October and deaths occurred from April to November. Rates of leaf and flower population change differ between treatments. The average life spans of leaves did not vary significantly between the five treatments but was longer in the control; the timing of births had a strong influence on the expectation of life. Stolon extension rates also varied quite markedly in the presence of different neighbours. A summary table is presented showing the array of responses displayed by this single genotype of T. repens L. in a range of environments.
USE OF THE INDIRECT IMMUNOFLUORESCENT TECHNIQUE TO STUDY THE VESICULAR‐ARBUSCULAR FUNGUS GLOMUS EPIGAEUM AND OTHER GLOMUS SPECIES
Authors: KOUGH J. , MALAJCZUK N. , LINDERMAN R. G.
Published: May 2006

Summary

An antiserum for spores and hyphae of Glomus epigaeum was developed employing extracted chlamydospore walls as an antigen. The reaction with fungal material was visualized by an indirect immunofluorescent technique. The staining was most intense and uniform on hyphae from root preparations and on the inner spore walls and hyphal attachments from spore preparations. The staining reaction was strongest for G. epigaeum, but G. mosseae and G. deserticola also reacted. The staining reaction appeared to be specific for the genus Glomus, as endomycorrhizal species of Gigaspora, Acaulospora and other soil and root‐inhabiting fungi tested did not react.
A NOTE ON THE RELATIVE PHOSPHORUS AND CALCIUM CONTENTS OF METACHROMATIC GRANULES IN FAGUS MYCORRHIZA
Authors: STRULLU D. G. , HARLEY J. L. , GOURRET J. P. , GARREC J. P.
Published: May 2006

Summary

The relative phosphorus and calcium contents of the phosphatic granules of Fagus mycorrhiza were measured before and after phosphate absorption from KH2PO4 solution. Whereas their phosphorus content greatly increased, their calcium content did not, so that the phosphorus: calcium ratio fell. These results are discussed in the context of the cation content of the granules and estimates of the amount of phosphate present in granule form.
THE EFFECT OF NITRATE AND PHOSPHATE ON THE VESICULAR‐ARBUSCULAR MYCORRHIZAL INFECTION OF LETTUCE
Authors: HEPPER CHRISTINE M.
Published: May 2006

The application of increasing amounts of nitrate resulted in higher levels of vesicular‐arbuscular mycorrhizal infection in lettuce roots inoculated with Glomus mosseae. This effect was found at three phosphate levels. The application of nutrient solutions containing different concentrations of nitrate and phosphate resulted in different nitrogen and phosphorus levels in the roots. At high concentrations of phosphorus in the roots, infection was inhibited, but at low concentrations the infection level appeared to be related to the nitrogen content of the host tissue. Mycorrhizal infections in low‐nitrogen treatments were poorly developed with very few arbuscules and intercellular hyphae. Two methods of estimating infection (gridline intersect and yield of glucosamine) were compared.
DIFFERENTIAL RESPONSE OF AZOLLA‐ANABAENA ASSOCIATIONS TO HIGH TEMPERATURE AND MINUS PHOSPHORUS TREATMENTS
Authors: TUNG H. F. , WATANABE I.
Published: May 2006

The response of Azolla species to high temperature and minus phosphorus (– P) treatments was investigated. Azolla filiculoides was judged the most sensitive to high temperature on the basis of its growth, acetylene reduction activity (ARA), losses in chlorophyll and protein content. The temperature‐tolerant strains like A. pinnata (Cheng Mai and Pu Tiang Zhu) and A. microphylla showed good growth and no senescence even after 6 weeks at 37/29°C provided that plant density was controlled and nutrients were not limiting.

The – P treatment reduced both growth and N2‐fixation in the Azolla plants. Its effect was greater on N2‐fixation as measured by ARA, than on growth in the first week of culture in a P‐deficient medium. High temperature did not hasten or enhance the appearance of P deficiency symptoms. A lower endogenous P content was needed to induce physiological disorder in A. pinnata than in A. mexicana and A. microphylla.
A PHYSIOLOGICAL INTERPRETATION OF THE DYNAMIC RESPONSES OF POPULATIONS OF A PLANKTONIC DIATOM TO PHYSICAL VARIABILITY OF THE ENVIRONMENT
Authors: REYNOLDS C. S.
Published: May 2006

Summary

The dynamic responses of Fragilaria crotonensis populations to artificial variations in the mixed depth of the water column of a Lund Tube (Enclosure C, Blelham Tarn) are shown to conform to a descriptive model involving only two environmental variables: mixed depth and optical depth. The physiological interpretation of these responses invokes a second model, relating the rates of net population change to photosynthetic productivity, corrected for respiration, and to in situ sinking loss rates. Population increases coincide with mixing episodes, when it is shown that the maximum photosynthetically‐derived growth rate exceeds the sinking low rate by an amount similar to the observed rate of net gain. Abrupt declines occur when the column rapidly restratifies, at rates explicable in terms of accelerated sinking and sinking‐loss rates, i.e. that there is also an abrupt cessation in growth. Evidence that this effect is due to extreme near‐surface photoinhibition is presented. The ecology of Fragilaria populations is briefly discussed in relation to these findings.
EVIDENCE THAT TEMPERATE EAST NORTH AMERICAN EVERGREEN WOODY PLANTS FOLLOW CORNER'S RULES
Authors: WHITE P. S.
Published: May 2006

Summary

Coener's rules, first developed for tropical trees, predict a spectrum of woody plant forms, from ones with small leaves, thin twigs (first‐year shoots) and many branches, to ones with larger Waves, thick twigs and few branches. These rules were confirmed for nine broad‐leaved and 12 needle‐leaved evergreen woody plants of temperate eastern North America: for each of these groups, leaf size was positively correlated with twig cross‐sectional area and both of these were negatively correlated with the number of twigs needed to bear 104 cm2 total leaf area. When compared to deciduous trees, characterized in a previous study, broad‐leaved evergreens had leaves that were 85% smaller at a given twig thickness and needed 750% more twigs to bear a given total leaf area (at least when leaves older than 1 year were ignored). Needle‐leaved evergreens bore relatively small leaves but large numbers of leaves per first‐year shoot; they bore fewer twigs per 104 cm2 total leaf area than broad‐leaved evergreens, but more than broad‐leaved deciduous species. Broad‐leaved deciduous trees were characterized by relatively large leaf sizes as a function of twig cross‐sectional area and low numbers of twigs per 104 cm2 total leaf area. Although Corner's rules are a significant index of plant form, a full resolution of the differences between deciduous and evergreen species awaits further study.
CENSUS OF AIRBORNE POLLEN GRAINS IN THE ATMOSPHERE OF ASCOLI PICENO (CENTRAL ITALY)
Authors: FRENGUELLI G. , MINCIGRUCCI G. , ROMANO B. , BRICCHI E.
Published: May 2006

Summary

Hirst's Volumetric Sampler was employed in the aerial survey of atmospheric pollen of Ascoli Piceno. Altogether 67 pollen types are recognized. The highest concentrations of airborne pollen occur in April, May, June, with pollen of Gramineae, Corylaceae, Fagaceae, Urticaceae and Oleaceae predominant.
WATER RELATIONS PARAMETERS OF TWO SICILIAN SPECIES OF SENECIO (GROUNDSEL) MEASURED BY THE PRESSURE BOMB TECHNIQUE
Authors: SALLEO S.
Published: May 2006

The possible role in drought resistance played by leaf water potential, osmotic potential, weight‐averaged turgor pressure and bulk modulus of elasticity is studied in mature and young leaves of Senecio Candidus and S. ambiguus. Small water losses cause relatively large reductions in leaf water potential in, S. candidus without greatly altering its osmotic potential. This occurs because S. candidus develops thicker leaf cell walls with high values of leaf bulk elastic modulus. Recovery from water stress is very rapid in this species. Leaf growth is influenced by the structural pattern of the cell walls in that S. candidus leaves complete their expansion within a shorter period of time than those of S. ambiguus. The possible adaptive significance of changing the leaf bulk modulus of elasticity in mature and young leaves of the two species is discussed.
GROWTH RESPONSES OF SITKA SPRUCE SEEDLINGS TO MYCORRHIZAL INOCULATION
Authors: THOMAS G. W. , JACKSON R. M.
Published: May 2006

Under glasshouse and field conditions, different mycorrhizal fungi differ in their effect upon the growth and nutrient status of seedlings of Sitka spruce [Picea sitchensis (Bong.) Carr]. Seedlings inoculated with ‘E‐strain’ fungi, the dominant mycorrhizal fungi of nurseries, and grown in forest soil in the glasshouse and in field plots were smaller than those inoculated with either Thelephora terrestris Ehrh. Fr. or Laccaria laccata (Scop, ex Fr.) Cooke.
INTERSPECIFIC PLANT ASSOCIATION EFFECTS ON VESICULAR–ARBUSCULAR MYCORRHIZA OCCURRENCE IN ATRIPLEX CONFERTIFOLIA
Authors: MILLER R. M. , MOORMAN T. B. , SCHMIDT S. K.
Published: May 2006

Earlier studies with the shrub Atriplex confertifolia (Chenopodiaceae) suggested that the occurrence of mycotrophy was related to the community from which root samples were obtained; plants in disturbed areas were non‐mycotrophic, while those growing in native areas possessed infection. Upon closer examination when neighbouring plants were studied, the level of mycorrhizal infection of Atriplex confertifolia was found to be related to its interspecific plant associations. When Atriplex confertifolia occurred solitarily, or in the presence of non‐mycorrhizal A. gardneri, it was non‐mycotrophic. However, when occurring near grasses or Artemisia spinescens, it possessed mycorrhiza infection. What appeared to be a community effect for the occurrence of mycorrhiza is nothing more than an association effect in which level of infection is related to the degree of mycorrhizal host plant cover. In disturbed communities little chance occurs for encountering a neighbouring mycorrhizal plant, while native plant communities are composed primarily of mycorrhizal counterparts.
CYTOKININS AND THE REGENERATION OF PLANTLETS FROM SECONDARY EMBRYOIDS OF WINTER OILSEED RAPE, BRASSIC A NAP US SSP. OLEIFERA
Authors: LOH C.‐S. , INGRAM D.S. , HANKE D. E.
Published: May 2006

It was shown that only a small proportion of haploid (= amphihaploid; n= 19) secondary embryoids of winter oilseed rape (Brassica napus ssp. oleifera) grew into plants when transferred to a medium without plant growth regulators. The majority grew abnormally and formed further secondary embryoids on their surfaces. It was then found by experiment that an effective method of inducing leaf initiation and reducing secondary embryogenesis was to transfer the secondary embryoids to a basal medium supplemented with 6‐furfurylaminopurine (kinetin; 10−4 M), alone or in combination with low concentrations of indole‐3‐acetic acid. Roots were initiated by further transfer of the cultures to basal medium without plant growth regulators. The plantlets so produced were normally haploid and were suitable for growing on into whole plants. The reduction of secondary embryogenesis by cytokinins is discussed in the general context of response by plant tissues to plant growth substances.
EFFECT OF IRRIGATION, WATER SALINITY AND ROOTSTOCK ON THE VERTICAL DISTRIBUTION OF VESICULAR‐ARBUSCULAR MYCORRHIZA IN CITRUS ROOTS
Authors: LEVY Y. , DODD J. , KRIKUN J.
Published: May 2006

The effects of rootstock, irrigation regime and water salinity on the vertical distribution of vesicular‐arbuscular mycorrhiza (VAM) of citrus roots were investigated in the field. Rootstocks differed in the uniformity of the vertical distribution of VAM, notably, Rough lemon exhibited a uniform vertical distribution and Sour orange a non‐uniform distribution with decreased VAM infection at depth. Decreasing the interval between irrigations reduced VAM infection of Sour orange, especially in the upper layers of soil. Increased salinity of irrigation‐water reduced VAM in deep layers of soil.
DEVENSIAN LATE‐GLACIAL AND FLANDRIAN VEGETATIONAL HISTORY AT HOCKHAM MERE, NORFOLK, ENGLAND
Authors: BENNETT K. D.
Published: May 2006

Analysis of the basin morphometry of Hockham Mere suggests that the lake basin is of a shape in which sediment is likely to be focused. Consideration of three long pollen diagrams through the deposits shows that focusing of organic post‐glacial sediment began at about 9255 B.P., and continued until the lake basin had filled, during the mid post‐glacial. The sediments deposited before 9255 B.P. are highly inorganic, and have remained concentrated near the edge of the basin, where they were initially deposited. The pollen accumulation rate diagram, from the deepest part of the basin, cannot be understood without considering the changing pattern of sediment distribution within the lake, and it is suggested that pollen concentrations may yield a more reliable interpretation of the development of vegetation in the surrounding landscape than can be obtained from pollen accumulation rates.
THE INFLUENCE OF PHYTOCHROME PHOTOEQUIILIBRIUM ON GIBBERELLIN‐LIKE SUBSTANCES AND CHLOROPHYLL CONTENT OF CHLOROPLASTS OF HORDEUM VULGARE L.
Authors: HILTON JANET R.
Published: May 2006

The mediation by phytochrome of the amount of gibberellin (GA)‐like substances extractable from etioplasts is well documented. Results presented here show that phytochrome mediates the amount of GA‐like substances extractable from Hordeum vulgare L. chloroplasts, and changes in the chlorophyll a/b ratio of chloroplasts. The results are discussed in relation to shade detection and the efficiency of photosynthesis in the natural environment.
THE DEVELOPMENT OF MYCORRHIZA ON SEEDLINGS OF FAGUS SYLVATICA L.
Authors: WARREN WILSON J. , HARLEY J. L.
Published: May 2006

In beech seedlings during their first growing season, both in pot experiments and in natural woodland conditions, the root tips passed through a developmental sequence in which the elongation rate progressively declined, root diameter decreased, the root cap became smaller, and tissue differentiation approached nearer to the apex. Such a spatially precocious differentiation is characteristic of mycorrhizas, where it has generally hitherto been regarded as a consequence of fungal infection, but in these seedlings it was a normal developmental change associated with progressive decline in activity of the root meristem, and was independent of the presence of mycorrhizal fungi. Indeed, mycorrhizal infection occurred only when a root tip had passed through this sequence and elongation had nearly or completely ceased. The formation of mycorrhiza caused a resumption of slow elongation, and a constriction in the root marked the position of the root tip at infection: the mycorrhizal region was swollen owing to cortical cells being expanded in the transverse plane. Certain features of the structure of the root of the host varied quantitatively with the species of mycorrhizal fungus. An attempt is made to identify those aspects of mycorrhizal structure which resulted from normal root development and those which were induced by the fungus.
PHYSIOLOGICAL STUDIES ON TEMPERATE LICHEN SPECIES I. A MATHEMATICAL MODEL TO PREDICT ASSIMILATION IN THE FIELD, BASED ON LABORATORY RESPONSES
Authors: PATERSON D. R. , PATERSON E. W. , KENWORTHY J. B.
Published: May 2006

Summary

A model has been constructed to predict assimilation in four lichen species using climatological data. Gas exchange of the lichens has been measured in the laboratory in response to seasonal, light, temperature and moisture changes. By fitting polynomial equations to the response curves, the model predicts assimilation on the basis of these variables. A comparison of weight changes measured in the field with assimilation values predicted by the model using climatological data measured in the field, shows that the model gives realistic predictions over periods of 1 month. The model also permits the importance of the various environmental parameters to be examined, singly and in combination. Predicted assimilation values on climatically different days suggest that moisture is the single most important factor governing lichen growth – the assimilation gains during one rainy summer day can counteract the losses of five dry days. The model can now be extended to examine possible reasons for lichen distribution.
UNUSUAL ‘TUBULAR CLUSTERS’ IN THE PLASTIDS OF A DUCKWEED (LEMNA PAUCICOSTATA) MUTANT INCAPABLE OF PHOTOSYNTHESIS AND AMMONIUM ION UPTAKE
Authors: MONSELISE EDNA BEN‐IZHAK , PORATH DAN , TAL MOSHE
Published: May 2006

Summary

Light‐grown plants of the wild type 6746 strain and the mutant strain 1073 of Lemna paucicostata were compared. It was confirmed that this photosynthetically defective mutant is dependent on supply of sucrose for its growth. Moreover it was found that it is unable to take up NH4+ in the absence of added sucrose; addition of a‐oxoglutarate did not allow ammonium ion uptake.

In the mutant, mitochondria are unusually long and distorted and in its chloroplasts the grana contain many more thylakoid membranes than in the wild‐type chloroplasts of the same age. Moreover, at all ages, the presence of specific new structures known as ‘tubular clusters’ can be detected; tubular clusters differ from prolamellar bodies found in etioplasts. In addition, both strains produced in young fronds, upon standing in darkness for 28 h, prolamella bodies with typical crystalline structure.

A possible connection between the tubular clusters and physiological aberrations of the mutant is discussed.
DINOPHYTE FLAGELLA: A COST‐BENEFIT ANALYSIS
Authors: RAVEN J. A. , RICHARDSON KATHERINE
Published: May 2006

Summary

The mobility of dinophytes allows them to migrate dielly, in a vertically stratified environment, between deeper regions where concentrations of nutrients (principally nitrate) are higher but light low, and less deep regions with lower nutrient concentrations but more light. When there is a substantial (several metres) depth range in which dinophytes can grow but, at any given depth, growth is restricted by both nitrate and light availability, vertical migration from a deeper station at night to a less deep station during the day could increase the availability of light and nitrate to a dinophyte cell over a complete light‐dark cycle.

Cost‐benefit analysis shows that the benefits of migration (increased acquisition of photons and nitrate relative to non‐migratory cells) could very substantially exceed the costs (the energy and nitrogen required to produce and operate the flagella apparatus and any additional nitrate or photon‐harvesting machinery which may be required as a result of migration). It is therefore concluded that, in some habitats, vertical migration could increase the growth rates of dinophytes. The occurrence of such increases under natural conditions, and their selective significance, await further investigation.
TAPHONOMY OF PROSPECTIVE PLANT MACROFOSSILS IN A RIVER CATCHMENT ON SPITSBERGEN
Authors: HOLYOAK D. T.
Published: May 2006

Summary

Representation of recent plant parts in fluvial sediments and in the vegetation of a braided‐river catchment on Spitsbergen was studied quantitatively in order to provide a model for taphonomy of plant macrofossils during cold stages of the British Pleistocene. The area studied on the Adventelva is in a region with continuous permafrost and on a river that has high (nival) peak discharges in early summer, features that were also present in the British lowlands during the Pleistocene cold stages.

Deposition of ‘prospective macrofossils’ in silts of channels on the Adventelva floodplain occurred mainly during the decline from the early summer peak of discharge. Surface runoff overland was much the most important process by which ‘prospective macrofossils’ reached river channels, and this accounts for them giving a surprisingly even overall representation of the abundance of similar parts in the vegetation. Taxa having ‘prospective macrofossil parts’ that were under‐represented in the deposits had parts that were: (a) very small, (b) of soft or perishable texture, (c) firmly attached to stems, (d) neither deciduous nor renewed annually, or (e) they were plants growing on the river floodplain. Taxa with parts over‐represented in the deposits were: (a) those with parts that break into numerous identifiable fragments, or (b) they were plants growing in localized areas of late snow‐lie.
BIOLOGICAL EFFECTS OF A HERBICIDE ON A NITROGEN‐FIXING CYANOBACTERIUM (BLUE‐GREEN ALGA): AN ATTEMPT FOR INTRODUCING HERBICIDE‐RESISTANCE
Authors: VAISHAMPAYAN A.
Published: May 2006

Summary

The herbicide monuron [3‐(4‐chlorophenyl)‐1, 1‐dimethylurea] inhibits growth and heterocyst formation in the nitrogen‐fixing cynobacterium Nostoc muscorum. These inhibitory effects are glucose‐reversible in both N2 (nitrogen‐free) and NO3− media. A spontaneous mutant of this cyanobacterium, resistant to a dose of monuron normally applied to the rice‐fields of North India, has been isolated and preliminarily characterized as having no requirement for an organic carbon source for its normal physiology under monuron‐treated conditions. The behaviour of the mutant has been tentatively explained as resulting from a permeation mutation preventing monuron entry into N. muscorum.
A CHLOROPLAST AND OTHER ORGANELLES OF PHASEOLUSVULGARIS WITHIN A HYPHA OF COLLETOTRICHUMLINDEMUTHIANUM
Authors: O'CONNELL R. J. , BAILEY J. A. , RICHMOND D. V.
Published: May 2006

Summary

In the course of an ultrastructural study of the anthracnose pathogen (Colletotrichum lindemuthianum) infecting hypocotyls of a susceptible cultivar of French bean (Phaseolus vulgaris), a chloroplast and other plant organdies were observed within the cytoplasm of a fungal hypha.

The chloroplast retained its morphological integrity and was not enclosed by an extra membrane derived from either plant or fungus. It is possible that the plant organelles entered the fungus through a rupture in the hyphal wail and plasmalemma that permitted cytoplasmic continuity between host and pathogen.
COLONIZATION OF THE ROOT SYSTEM OF SUBTERRANEAN CLOVER BY THREE SPECIES OF VESICULAR‐ARBUSCULAR MYCORRHIZAL FUNGI
Authors: ABBOTT L. K. , ROBSON A. D.
Published: May 2006

Summary

Subterranean clover infected by Glomus fasciculatum was transplanted into soil containing propagules of two other species of vesicular‐arbuscular mycorrhizal fungi: Acaulospora laevis and Glomus tenue. Root temperatures were maintained at either 15 or 20 °C and the soil was either watered to 80% of field capacity for 3 weeks or left dry before the seedlings were transplanted. Glomus fasciculatum spread well from existing infection except when the soil contained a highly‐infective population of A. laevis. Infection by A. laevis was more rapid at 20 than at 15 °C and was greatly enhanced by pre‐wetting of soil. The lag phase in the development of infection was greater for G. tenue than it was for A. laevis. High values for the percentage of the root length infected by G. tenue were recorded only in plants in which infection by A. laevis did not develop rapidly. There was no effect of G. fasciculatum in the transplanted seedlings on the level of infection formed by A. laevis; at 20 °C the percentage root length infected by G. tenue was lower when plants had been infected by G. fasciculatum. Irrespective of species, the fungus which infected most rapidly in each case had the competitive advantage, probably due to its prior occupancy of the root.
MECHANISMS FAVOURING OUTBREEDING IN STRIGA HERMONTHICA [SCROPHULARIACEAE]
Authors: SAFA S. B. , JONES B. M. G. , MUSSELMAN L. J.
Published: May 2006

Summary

Self‐incompatibility has been demonstrated in two samples of the parasitic flowering plant, Striga hermonthica, originating from Upper Volta and Sudan. Compatibility was determined by fluorescence microscopy of stigmatic preparations following controlled pollinations. Self incompatibility was associated with floral adaptations favouring pollination by long‐tongued insects such as butterflies. Outbreeding accounts for the variability of S. hermonthica, both in morphology and in host‐specificity. Genetic variation in host specificity imposes limits upon the effectiveness of the present methods of testing tropical cereals for resistance to S. hermonthica.
ECTOTYPIC DIFFERENTIATION IN POA ANNUA: WITHIN POPULATION VARIATION IN RESPONSE TO COMPETITION AND CUTTING
Authors: McNEILLY T.
Published: May 2006

Summary

Dry weight production of seed‐derived material of eight genotypes from each of two populations of Poa annua, one from an open and the other from a closed habitat, was compared as pure stands and in mixture with Lolium perenne cv. S23. Comparisons were made in a glasshouse experiment after 13 weeks growth, when uncut, and when cut to a height of 1.5 cm at 5, 7, 9, II and 13 weeks from planting‐ Significant differences were found between genotypes within both populations when cut in pure stands and in mixture with Lolium, and also in uncut stands in mixture with Lolium. When uncut and in pure stands inter‐genotypic differences were found only in the open population. Between population differences in within population variation were significant only when the populations were cut and in mixed stands, the open population being more variable. The closed population was significantly more variable when uncut and in mixed stands than in any other treatment combination, whilst the open population did not vary significantly with treatment. The occurrence of genetically‐based inter‐population differences in competitive ability in P. annua is confirmed.
PHOTOMORPHOGENIC REGULATION OF REPRODUCTIVE DEVELOPMENT IN GROUNDNUT AND THE SIGNIFICANCE OF NYCTINASTIC LEAF MOVEMENTS
Authors: KARVE A. D. , DESHMUKH A. K. , BHALERAO A. C. , DESHMUKH V. A.
Published: May 2006

Summary

Many leguminous species are grown under relatively high plant population densities > 250000 plants ha−1. It is argued that these plants can tolerate high population densities because their nyctinastic leaf movements allow their aerial parts to receive directly the last light of the day, which increases the Pfr level in the plants before the onset of darkness, causing them to develop like unshaded plants. Measurements of irradiance above and below the canopy of a densely planted crop of groundnut (Arachis hypogaea fastigiata Waldron) showed that, during daytime, when the leaf laminae were horizontally orientated, only 10% of the incident light reached the ground, while after sunset, with the leaves in the vertical position, 70 to 90 % of the incident light could penetrate to the ground. Natural light, available to the plants after this time, was capable of inducing the straightening of hypocotyl hooks of dark‐germinated seedlings, a typical red light requiring photomorphogenic reaction. Laboratory experiments showed that groundnut plants, receiving daily 5 min red light immediately after the end of the photoperiod, developed significantly more branches and more reproductive organs than plants receiving 10 min far red light. The greater adaptability of two leguminous plants, bush bean (Phaseolus vulgaris L.) and groundnut, to high population density was demonstrated by comparing their performance with that of maize (Zea mays L.), okra (Abelmoschus esculentus Moench), safflower (Carthamus tinctorius L.) and sesame (Sesamum indicum L.) under a high and a low population density. Although crowding caused the plants of all six species to grow taller, with fewer branches and fewer reproductive organs, the harvest index of the two leguminous species remained unaffected by the population density, while that of the remaining four species was significantly reduced by the higher population density.
THE EFFECTS OF DESICCATION ON CONCENTRATIONS AND a/b RATIOS OF CHLOROPHYLL IN LEUCOBRYUM GLAUCUM AND THUIDIUM DELICATULUM
Authors: MARTIN C. E. , WARNER D. A.
Published: May 2006

Summary

Leaves of shade plants typically have higher concentrations, and lower a/b ratios of chlorophyll than do leaves of sun plants. In poikilohydric mosses as in vascular plants, such differences in concentration have been interpreted either as adaptations which enhance light capture or, in the more exposed mosses, as degradation of chlorophyll owing to water stress. There were no significant correlations between degree of hydration and either concentration or a/b ratios of chlorophyll in tissues of Leucobryum glaucum (Hedw.) Angustt. ex Fr. and Thuidium delicatulum (Hedw.) B.S.G. exposed to increasing water stress. As these data do not support the latter hypothesis, it is concluded that the former explanation is probably valid.
A RELATIONSHIP BETWEEN PHYTOCHROME PHOTOEQUILIBRIUM AND GERMINATION OF SEEDS OF POA TRIVIALIS L. FROM CONTRASTING HABITATS
Authors: HILTON JANET R. , FROUD‐WILLIAMS R. J. , DIXON J.
Published: May 2006

Summary

Poa trivialis L, (rough meadow grass) is an indigenous grass weed of both arable and grassland situations. The effect of light quality on the germination of seed collected from both these habitats was compared. Seed from open, arable habitats germinated poorly when exposed to light giving a Pfr/P ratio similar to that of shade light. In contrast, germination of seed from closed, grassland habitats was much less inhibited indicating that seed germination behaviour may be adapted to the habitat in which the seed was matured. Differences in seed germination behaviour were also observed when seed was buried at various depths in soil under conditions where differences in light quality could be discounted. The results are discussed in relation to the ecological significance of different sensitivities to environmental factors known to influence germination behaviour.
PHOSPHATE UPTAKE BY GOODYERA REPENS IN RELATION TO MYCORRHIZAL INFECTION
Authors: ALEXANDER CLARE , ALEXANDER I. J. , HADLEY G.
Published: May 2006

Summary

The rate of P uptake per unit length of root of adult plants of the orchid Goodyera repens Br., infected with the mycorrhizal endophyte Rhizoctonia goodyerae‐repentis Constantin and Dufour, was up to 100 times greater than that of non‐mycorrhizal plants. When the active extramatrical mycelium was reduced by treatment with thiabendazole fungicide, the relative growth rate of mycorrhizal plants was reduced in low P conditions but not in P rich conditions. Rates of P uptake into fungicide‐treated plants were Jess than those of mycorrhizal plants at both P levels. Translocation of 32P from a point source to the plant via the extramatrical mycelium was demonstrated and could be inhibited by the application of thiabendazole. In a model system incorporating a perlite/Vermiculite substrate, translocation of 32P via the endophyte took place over distances up to 9 cm. The mycorrhiza of adult G. repens appears similar to other mycorrhizas in its ability to enhance growth and P uptake.
COMPETITION FOR INFECTION BETWEEN VESICULAR‐ARBUSCULAR MYCORRHIZAL FUNGI
Authors: Wilson J. M.
Published: May 2006

Summary

The competitive abilities of three VAM fungi were investigated. Various pairs of fungi were interacted and the amounts of infection produced by mixed and single inocula were compared. The outcome of the interactions varied according to the fungi involved. Aggressiveness appeared to be inversely related to infectivity. In the interactions examined, both Glomus fasciculatum (Thaxter sensu Gerdemann) Gerdemann & Trappe and Glomus tenue (Greenall) Hall were less aggressive than Gigaspora decipiens Hall and Abbott. No interaction occurred between Gl. fasciculatum and GL tenue. Except in the interaction between Gl. fascicidatum and Gi. decipiens, the total amount of infection formed by mixed inoculation was similar to that formed by single inoculation of the more infective fungus of the interacting pair. The outcome of the interactions were shown to be affected, in some circumstances, by inoculum frequency, time of harvest, most incubation of the inoculum, and the spatial distributions of the interacting propagules.
SELENIUM TOXICITY IN PERENNIAL RYEGRASS AND WHITE CLOVER
Authors: SMITH G. S. , WATKINSON J. H.
Published: May 2006

Summary

Shoot concentrations of Se associated with a 10% reduction in dry matter yield were established for perennial ryegrass (Loliumperenne L.) and white clover (Trifolium repens L.) grown in sand culture. Selenite– treated plants had lower shoot concentrations of Se than those treated with selenate; the critical toxic values associated with a 10% reduction in growth were 48 and 320μg Se g− 1 dry matter shoots for ryegrass plants, and 160 and 330μeg1 dry matter shoots for white clover plants, respectively. Differences in the mode of absorption of selenite and selenate, and in the distribution and chemical form of Se found in the plant after absorption, probably account for this disparity in toxicity. While both selenate and selenite increased the Se concentration in the tissues of the plants to high levels, a greater proportion of the absorbed Se was transported to the shoots of the selenate‐treated plants than of those treated with selenite. Increasing supplies of selenate were associated with a reduction in chlorophyll content. Contrary to the concept of a common uptake mechanism in the roots for selenate and sulphate, increasing supplies of selenate had a synergistic effect on S concentrations in the shoots rather than the expected antagonistic effect.
EFFECT OF PHOTOPERIOD AND WATER SUPPLY ON APICAL ABSCISSION OF LONG‐SHOOTS OF TILIA CORDATA MILL.
Authors: PIGOTT C. D.
Published: May 2006

Summary

Growth of long‐shoots of Tilia cordata Mill, is sympodial and indeterminate. Abscission of the apex occurs rapidly in short days. In natural conditions abscission occurs in a large proportion of shoots before, or shortly after, the summer solstice when daylength is 17 to 18 h. An experimental study shows that even in long days, if plants are pot‐bound and watered infrequently, apical abscission occurs within a few days of the buds opening. Transferring plants to a large volume of soil or watering frequently delays abscission for several weeks. On a high proportion of plants, which have been either exposed to short days, or deprived of water, defoliation in early or midsummer causes the buds to open, but by late summer buds on the majority of plants are dormant.
HABITAT REQUIREMENTS IN PRIMULA SPECIES
Authors: WHALE D. M.
Published: May 2006

Summary

The habitat requirements of Primula vulgaris Huds., P. veris L. and P. elatior (L.) Hill are discussed in terms of their tolerance to waterlogging, drought and shade. Hypotheses generated from this discussion are presented pictorialry and examined in the light of results from competition and field experiments. It is concluded that differences in tolerances to these factors are sufficient to account for the observed habitat requirements, but that the influence of grazing, in particular, can have a strong moderating influence. Grazing pressure varied between the natural habitat types of the species.
BIOCHEMICAL AND PHYSIOLOGICAL ASPECTS OF LEAF DEVELOPMENT IN COCOA (THEOBROMA CACAO L.)
Authors: ABO‐HAMED S. , COLLIN H. A. , HARDWICK K.
Published: May 2006

Summary

The export and translocation of radioactivity supplied as 14C‐auxin or as a 14C‐kinin to a donor leaf of cocoa was followed at different stages of the flush cycle to see whether there was any correlation between the pattern of movement of these growth promoters and apical bud activity. The auxin 3‐indole (1‐14C) acetic acid, (14C‐IAA), and the cytokinin, 6‐benzyI‐amino (8‐14C) purine, (14C‐BAP), were introduced into the plant by foliar feeding. Export of the radioactivity derived from the 14C‐IAA was predominantly basipetal at all stages of the flush cycle. Most of the tracer accumulated in the lower stem but there was a significantly high proportion in the older leaves. It appeared that the largest proportion of the radioactivity derived from 14C‐IAA was found in parts of the plant where growth, or possibly carbohydrate accumulation, was active. It is suggested that the movement of 14C‐IAA and its metabolites in cocoa may be largely determined by the direction of flow of the assimilate stream. The identity of the radioactive compounds exported from the donor leaf showed that some 80 % of the fed 14C‐IAA was metabolized to other indole compounds including indole aldehyde, indole aspartate and indole acetonitrile.

When the 14C present in particular plant parts was expressed as a relative radioactivity ratio, this value, for the apical bud, declined throughout the flush cycle, being highest at bud break, indicating that the capacity of the bud to accumulate radioactivity derived from 14C‐IAA was greatest during the stages of leaf production.

The distribution of radioactivity from 14C‐BAP indicated both acropetal and basipetal transport of cytokinin but accumulation of radioactivity occurred only in actively growing regions. Unlike 14C‐IAA, the 14C‐BAP exported from the leaf was not extensively metabolized and about 60% of the transported radioactivity was detected as 14C‐BAP and the remainder as conjugated 14C‐BAP. For this compound the relative radioactivity ratio in the bud was highest at dormancy break (F‐1), suggesting that cytokinin movement to the bud was related to the breaking of dormancy. The changes in pattern of transport of auxin and cytokinin throughout the cocoa plant were correlated with the stages of the flush cycle.
DIURNAL CHANGES IN WATER RELATIONS AND ABSCISIC ACID IN FIELD‐GROWN VITIS VINIFERA CULTIVARS
Authors: LOVEYS B. R.
Published: May 2006

Summary

Diurnal changes in stomatal conductance and accompanying changes in the abscisic acid (ABA) content of expressed xylem sap were studied in unstressed grapevines (Vitis vinifera L. cvs Riesling and Silvaner) growing in the field in Adelaide, South Australia. Stomatal conductance increased rapidly during the early morning reaching a maximum in both cultivars at about 1000 h. Conductance during the latter part of the day was considerably reduced despite relatively mild environmental conditions.

Quantitative analysis of ABA in untreated sap was carried out by high performance liquid chromatography (HPLC). The concentration of ABA in xylem sap varied from 1.5 × 10−4 mol m−3in the morning to 5 × 10−4 mol m−3in the late afternoon. Uptake of ABA from the xylem adequately accounted for diurnal changes in leaf ABA.

Gas exchange analysis of detached field‐grown leaves showed that ABA, supplied via the transpiration stream, caused substantial reductions in stomatal conductance and assimilation when supplied at a concentration equivalent to that in xylem sap [5 × 10−4 mol m−3 (+) ABA]. The reduction in assimilation was entirely stomatal in origin.

It is suggested that ABA uptake from the xylem causes partial stomatal closure during the afternoon and plays a key role in the control of stomatal conductance in field grown vines by optimizing the relationship between CO2 uptake and water loss.