bluuebunny/crossref_metadata_2025 huggingface dataset:
THE EFFECT OF TEMPERATURE ON THE SURVIVAL OF DRY BRYOPHYTES
Authors: HEARNSHAW G. F. , PROCTOR M. C. F.
Published: May 2006

Summary

Loss of viability by seven species of bryophyte (Anomodon viticulosus, Racomitrium aquaticum, R. lanuginosum, Tortula intermedia, Andreaea rothii, Frullania tamarisci and Porella platyphylla) kept dry at temperatures between 20 and 100 °C was followed by estimating chlorophyll content after a moist recovery period. Behaviour at different temperatures was qualitatively similar, differing in time‐scale. This ranged from a few minutes or less for 50% loss of chlorophyll at 100 °C to weeks or months for the more resistant species at 37 and 20 °C.

For most of the species investigated, the logarithms of the half‐viability times gave straight lines when plotted against the reciprocal of absolute temperature, with little variation of slope between species. The relation is similar to that shown by dry seeds and extrapolation suggests half‐viability times of many years for the more desiccation‐tolerant bryophytes at 0 °C or below. The two Racomitrium species showed curvilinear relationships, with notably great tolerance at temperatures in the middle part of the range investigated.
ESTABLISHMENT OF AN EFFECTIVE ENDOMYCORRHIZAL ASSOCIATION ON CASSAVA IN FLOWING SOLUTION CULTURE AND ITS EFFECTS ON PHOSPHORUS NUTRITION
Authors: HOWELER R. H. , ASHER C. J. , EDWARDS D. G.
Published: May 2006

Summary

Eight cassava (Manihot esculenta) cultivars were grown with or without mycorrhizal inoculation in flowing solution cultures containing approximately 0.1, 1, 10 or 100 μM phosphate. Rice (Oryza sativa), maize (Zea mays), cowpea (Vigna unguiculata) and French bean (Phaseolus vulgaris) were included in the experiment for comparative purposes.

Cassava required a higher external phosphorus concentration for maximum yield (≥ 10 μM) than the other species (≥ 1 μM) regardless of the inoculation treatments. Roots of inoculated cassava plants were heavily infected with VA endophytes at 0.1 and 1 μM phosphate, but not at 10 or 100 μM. Non‐inoculated cassava plants were free of infection, and no infections were observed in any treatment on the other species.

At 1 μM phosphate, infection of cassava roots was associated with large increases in whole plant dry wt, concentration of phosphorous in tops and roots, and total phosphorus uptake. At 0.1 μM phosphate there were also substantial increases in phosphorus concentration in tops and roots but the infected cassava plants were still severely phosphorus deficient and growth was not improved.

The results are discussed in relation to the present state of knowledge about the phosphorus nutrition of cassava.
THE ROLE OF EXCHANGEABLE CALCIUM IN SAXICOLOUS CALCICOLE AND CALCIFUGE MOSSES
Authors: BATES J. W.
Published: May 2006

Summary

Species of bryophyte restricted to calcareous rocks in the British Isles consistently exhibit concentrations of calcium 16 to 17 times greater than in species found on non‐calcareous rocks. In both groups of plants, this calcium is predominantly in an exchangeable form. Experiments in which the exchange sites were saturated with Ca2+ ions indicate that the calcicoles have Ca2+ exchange capacities three or four times those of the calcifuges. Several possible explanations for this difference are discussed. One hypothesis, that a high affinity for Ca2+ ions corresponds with a high calcium requirement for permeability control, has been tested experimentally. The results, although far from conclusive, suggest that calcicole mosses may require enriched Ca2+ concentrations in their tissues to maintain the integrity of their cell membranes.
CATION COTOLERANCE IN A SALT‐TOLERANT CLONE OF AGROSTIS STOLONIFERA L.
Authors: HODSON M. J. , SMITH M. M. , WAINWRIGHT S. J. , ÖPIK H.
Published: May 2006

Summary

The tolerance of clones of Agrostis stolonifera from salt marsh and inland habitats to the chlorides of lithium, sodium, potassium, rubidium, caesium, magnesium and calcium was measured in water culture by a rooting index of tolerance technique. The salt marsh clone was always more tolerant than the inland clone. This was confirmed for LiCl, NaCl and KCl in separate experiments in which dry wt increments were measured. It is suggested that the evolution of tolerance to NaCl in the salt marsh clone has conferred cotolerance to the other alkali metal chlorides, and that the toxicity of LiCl, RbCl and CsCl at least, results from their cations and is not due to chloride ions nor to osmotic stress. Tolerance towards the two alkaline earth chlorides MgCl2 and CaCl2 was also examined. It is suggested that selection for MgCl2 tolerance may have taken place in the salt marsh clone, and that this tolerance has conferred tolerance to CaCl2.
THE INFLUENCE OF A SPRINGTAIL FOLSOMIA CANDIDA (INSECTA, COLLEMBOLA) ON THE MYCORRHIZAL ASSOCIATION OF LEEK ALLIUM PORRUM AND THE VESICULAR‐ARBUSCULAR MYCORRHIZAL ENDOPHYTE GLOMUS FASCICULATUS
Authors: WARNOCK A. J. , FITTER A. H. , USHER M. B.
Published: May 2006

Summary

Seedlings of leek were grown in a factorial experiment to examine the interactions between mycorrhizal infection with Glomus fasciculatus, soil teachings and the Collembola, Folsomia Candida. The growth of leek was increased by mycorrhizal infection and leachings, the latter having a lesser effect, and reduced by F. Candida. There was a strong interaction between the effects of mycorrhizal infection and the presence of F. Candida since infected plants in pots with the Collembola grew little better than uninfected plants. Evidence from root weight ratios, phosphate inflows and the gut contents of the Collembola all suggest that this is due to grazing of the external hyphae of G. fasciculatus, so rendering the infection ineffective.
THE BREEDING SYSTEM IN PRIMULA VERIS L.
Authors: RICHARDS A. J. , IBRAHIM HALIJAH BT.
Published: May 2006

Summary

Modern textbook accounts of within‐morph incompatibility in Primula usually assume that it is total, or nearly so. However, few published accounts can be traced concerning the efficiency of the incompatibility. These suggest that it is total in P. obconica, but rather weak in P. vulgaris, P. veris, P. auricula and P. sinensis.

Our work in P. veris suggests that for one population, within‐morph incompatibility is nearly total at normal temperatures. The mechanism of incompatibility varies between the morphs. In within‐pin pollinations, pollen germination is good, and tubes short and broad, being apparently unable to penetrate stigma papillae for physical reasons.

In within‐thrum pollinations, pollen germination is poor and the few tubes produced are broad and misshapen. These and the surrounding stigma papillae fluoresce strongly, and similar effects can be produced with pollen‐free water extracts.

A tentative model of the control of incompatibility in Primula is based on an enzyme dimer mode of action.
THE POLLINATION ECOLOGY OF ORCHIS GALILAEA (BORNM. ET SCHULZE) SCHLTR. (ORCHIDACEAE)
Authors: BINO R. J. , DAFNI A. , MEEUSE A. D. J.
Published: May 2006

Summary

The flower of Orchis galilaea (Bornm. et Schulze) Schltr. does not contain nectar. Only the males of Halictus marginatus are attracted and pollinate the orchid; females visit the flowers of other plant families. We suggest that O. galilaea has evolved a pollination mechanism based on a sexual attraction specific for the males of H. marginatus. This sexual attraction is the result of the strong, musk‐like scent.
TRACHEARY OCCLUSION IN FRONDS OF PTERIDIUM AQUILINUM (L.) KUHN SHOWING APOSPORY
Authors: SHEFFIELD E. , BELL P. R. , LAIRD S.
Published: May 2006

Summary

The occlusion of tracheids in aposporous fronds of Pteridium aquilinum attached to parent plants was found to account for the failure of dye to penetrate to the leaf extremities. The agent responsible for this blockage was seen as an electron‐opaque layer covering the walls and areas of overlap between tracheids. The aposporous behaviour of attached leaves is attributed to the discontinuation in supply of some influence from the parent plant which results from the tracheary occlusion observed.
POLLEN ANALYSIS OF AN INTERGLACIAL DEPOSIT AT WEST ANGLE, DYFED, WALES
Authors: STEVENSON A. C. , MOORE P. D.
Published: May 2006

Summary

A series of clays and muds underlying head deposits, exposed in a cliff section at West Angle, Dyfed, has been subjected to pollen analysis. Four pollen assemblage zones are described, all being dominated by temperate forest taxa, but with Pinus, Picea and Abies all present in some quantity. Forest disturbances are evident within the profile, in which light‐demanding taxa such as Fraxinus, Juniperus and Corylus become more frequent, as do many herbaceous types. Possible causes of these disturbances are considered, the most likely being local flood catastrophes. It is not possible fully to correlate the pollen sequence with other British and Irish interglacials, but certain features compare closely to some Hoxnian diagrams of eastern England. These are: (i) the presence of Abies, (ii) the occurrence of Picea through the entire profile, (iii) the consistent presence of Tilia in the middle two zones and (iv) the lack of Carpinus maximum.
MID‐FLANDRIAN FOREST HISTORY OF ROUDSEA WOOD NATIONAL NATURE RESERVE, CUMBRIA
Authors: BIRKS H. J. B.
Published: May 2006

Summary

A pollen‐stratigraphic record from a small (25 m diameter) hollow situated within the Carboniferous limestone area of Roudsea Wood is presented. The record extends from 6680 to 5150 years B.P. and shows that the canopy of the mid‐Flandrian forest around the hollow contained 10 to 30%Quercus, 5 to 15%Betula, 2 to 15%Ulmus cf. U. glabra, 5 to 25%Tilia cordata, 5 to 25%Fraxinus excelsior, 15 to 20%Alnus glutinosa, and 10 to 30%Corylus avellana. Minor trees and shrubs were also present, including Acer campestre, Euonymus europaeus, Rhamnus catharticus, Sorbus torminalis, and Thelycrania sanguinea, all of which grow today at or near their northern British limits near Roudsea Wood.
PHOTOMORPHOGENESIS IN IMPATIENS PARVIFLORA AND OTHER PLANT SPECIES UNDER SIMULATED NATURAL CANOPY RADIATIONS
Authors: WHITELAM G. C. , JOHNSON C. B.
Published: May 2006

Summary

Nitrate reductase activity in the leaves of Sinapis alba L. and Chenopodium album L. was found to be related to the photoequilibrium of phytochrome established under simulated natural canopy radiation (fluorescent white light with added far‐red light) of a relatively high photon fluence rate. Under simulated canopy radiation of low photon fluence rate, more characteristic of ‘shade’ light, the degree of responsiveness of S. alba nitrate reductase has been seen to be reduced. However, in the leaves of Impatiens parviflora L., a species frequently occurring in dense canopy shade, nitrate reductase activity showed a rapid and marked response to changes in phytochrome photoequilibrium with the low‐fluence rate sources. Under these same conditions the elongation growth of I. parviflora internodes also showed a marked and rapid response to changes in the phytochrome system, rather than displaying a reduced response as has been proposed for shade tolerating species.
THE EFFECT OF A MUTATION CAUSING ALCOHOL DEHYDROGENASE DEFICIENCY ON FLOODING TOLERANCE IN BARLEY
Authors: HARBERD N. P. , EDWARDS K. J. R.
Published: May 2006

Summary

Adh1‐M9 mutant barley plants lack a functional ADH1 gene product. The effect of this deficiency in alcohol dehydrogenase (ADH) activity on flooding tolerance is investigated by comparing the behaviour of mutant and wild‐type plants in flooded conditions. It is concluded that there is a specific requirement for a functional ADH1 polypeptide in the immersed seed but not at later stages of development. The significance of these findings is discussed with respect to current theories of flooding tolerance.
INTERACTION OF PHOTOPERIOD AND VESICULAR‐ARBUSCULAR MYCORRHIZAE ON GROWTH AND METABOLISM OF SWEET ORANGE
Authors: JOHNSON C. R. , MENGE J. A. , SCHWAB S. , TING I. P.
Published: May 2006

Summary

Vesicular‐arbuscular (VA) mycorrhizal infection and growth of Citrus sinensis were increased by longer photoperiods. Photosynthesis and stomatal conductances were greater for mycorrhizal plants, but were unaffected by daylength. Phosphorus levels in leaf tissue from mycorrhizal plants were threefold greater than those in non‐mycorrhizal plants and P levels were slightly greater in plants grown under long‐day photoperiods. Root exudation of reducing sugars was greatest for non‐mycorrhizal plants grown under long day photoperiods, but exudation of amino acids was variable. The results suggested that plants grown under long‐day photoperiods have greater basipetal transport of photosynthates resulting in improved mycorrhizal infection and plant growth response.
EFFECT OF FLOWER BUD DEVELOPMENT IN CHRYSANTHEMUM ON VESICULAR‐ARBUSCULAR MYCORRHIZA FORMATION
Authors: JOHNSON C. R. , GRAHAM J. H. , LEONARD R. T. , MENGE J. A.
Published: May 2006

Summary

Roots of single stem Chrysanthemum morifolium plants were inoculated with the vesicular‐arbuscular mycorrhizal (VAM) fungus, Glomus fasciculatus, at several stages of flower bud development. Compared to vegetative control plants, VAM formation was reduced during early stages of flower bud development, but not during later bud expansion. A decrease of reducing sugars and amino acids in root extracts during early bud development coincided with a decrease in root exudation of these compounds. These results suggest that reduction of VAM formation during early flower bud development resulted from a decrease in the availability and net leakage of metabolites necessary to sustain the mycorrhizal fungus during pre‐ and post‐infection.
PHYSIOLOGICAL‐ENVIRONMENTAL INTERACTIONS IN LICHENS
Authors: KERSHAW K. A. , MACFARLANE J. D.
Published: May 2006

Summary

The seasonal response matrix of gas exchange and nitrogenase activity in Collema furfuraceum is presented for a number of factorial combinations of light, thallus temperature (5, 15, 25 and 30 to 35 °C) and thallus water content, throughout the year. The results indicate C. furfuraceum is adapted both to the relatively xeric environment of its cortieolous habitat as well as to the low temperatures experienced in its low‐arctic environment. Of particular interest is the absence of a summer thermal stress response, which eliminates or severely reduces nitrogenase activity during the summer months in some lichens growing in more southerly localities. Equally, ambient temperatures during the winter, which can drop to minus 41 °C, do not affect nitrogenase activity and confirm the resistance of the nitrogenase enzymes in the intact thallus, to low temperatures.

There is a remarkable degree of uniformity in the net photosynthetic response matrix, at most light levels, at all experimental temperatures and at all times of the year. The total absence of seasonal photosynthetic acclimation as well as the seasonal constancy of photosynthetic capacity is discussed in terms of differential strategies in contrasting environments.
LIFE HISTORIES AND DEMOGRAPHY OF SHADE‐TOLERANT TEMPERATE FOREST HERBS: A REVIEW
Authors: BIERZYCHUDEK PAULETTE
Published: May 2006

Summary

Information is reviewed on the life histories and demographic patterns of shade‐tolerant herbs of temperate deciduous forest. Most of the species that have been studied are deciduous perennials. These species generally have a juvenile (non‐flowering) period of several years followed by an extended period of flower and seed production. About half the species reviewed are self‐incompatible, the others are at least partially self‐compatible. Although vegetative reproduction is common, replacement does not always occur by vegetative spread; many species appear to be able to replace themselves by seed. Sexual reproductive effort ranges from 1–5 to 50 % among the species reviewed; seed weight averages 2–6 mg. Short dormancy periods (one season) are most common, with germination rates generally below 50%.

Mortality rates of small plants are high, but decline as plant size increases. ‘Ageing’ does not appear to occur. No information exists on population growth rates of temperate deciduous forest herbs, or on the temporal stability of their population sizes or structures. The transition matrix model is suggested as a promising approach to future studies in plant demography.
PLANT‐INDUCED CHANGES IN THE RHIZOSPHERE OF RAPE (BRASSICA NAPUS VAR. EMERALD) SEEDLINGS
Authors: HEDLEY M. J. , NYE P. H. , WHITE R. E.
Published: May 2006

Changes in the rhizosphere pH of rape plants (Brassica napus var. Emerald), grown at high root densities (> 90 cm cm−3) in a soil of low P status, were not associated with any detectable increase in the amount of extractable organic acids or their anions, or in the total amount of uronic acids in the soil. Microbial numbers in the rhizosphere soil and unplanted control soil were estimated by dilution plate counting, using an hydroxyapatite (HA) agar substrate, and those colonies capable of producing acid or of dissolving HA were identified. Neither the total number of colonies nor the number of acid‐producing colonies and P solubilizing colonies bore any obvious relationship to the pH of the soil from which they were isolated. However, analysis of the major cation and anion concentrations in the plant tissue showed that more cations than anions were taken up by the rape plants during the period when the rhizosphere pH decreased. The milliequivalents of H+ or OH− required to produce the observed pH changes were calculated from the soil's pH buffer curve and found to agree closely with the difference between the milliequivalents of cations and anions taken up by the plant. A steady decline in NO3− uptake and a small increase in Ca2+ uptake created the cation‐anion imbalance during the period of decreasing rhizosphere pH. H+ release from the roots must have occurred to maintain the charge balance across the root‐soil interface and was the most likely cause of decrease in rhizosphere pH.
CYTOKININ PRODUCTION BY ECTOMYCORRHIZAL FUNGI
Authors: NG P. P. , COLE A. L. J. , JAMESON P. E. , MCWHA J. A.
Published: May 2006

The mycorrhizal fungi Rhizopogon luteolus Fr. and Nordh, Boletus elegans Schum. ex. Fr. and Suillus tuteus L. ex Fr., were investigated for cytokinin production in vitro. Culture filtrates in which the fungi had been growing for at least 2 weeks showed cytokinin activity when purified and bioassayed using soybean callus tissues. The cytokinin activity in the culture filtrate increased with longer periods of incubation. A potent inhibitor of callus growth from Boletus elegans culture filtrate which masks cytokinin activity is discussed.
STRUCTURE AND PHYSIOLOGY OF ECTOMYCORRHIZAE
Authors: NYLUND JAN‐ERIK , UNESTAM TORGNY
Published: May 2006

The process of mycorrhiza formation in previously uninfected roots was studied in vitro, using the fungus Piloderma croceum Erikss. & Hjortst, and the Norway spruce, Picea abies (L.) Karst, as model organisms. The process could be divided into the following phases: fungal growth stimulation by root metabolites; formation of a hyphal envelope on the root; intercellular penetration by single hyphae, change in fungal morphology into labyrinthic tissue formation leading to Hartig net formation, and extension of labyrinthic tissue to form a mantle. P. croceum, growing in dead tissue, showed saprophytic growth in vitro, a capacity suppressed in living tissue. The way of fungal penetration appeared to be mechanical. A hypothetical model for host‐fungus interactions regulating the mycorrhiza infection process is also discussed.
THE ENZYMES OF POLYPHOSPHATE METABOLISM IN VESICULAR‐ARBUSCULAR MYCORRHIZAS
Authors: CAPACCIO L. C. M. , CALLOW J. A.
Published: May 2006

The presence and distribution of enzymes of polyphosphate (polyP) synthesis and degrActation was examined in mycorrhizal and non‐mycorrhizal onion roots, and both external and internal hyphae of the endophyte, Glomus mosseae. PolyP kinase activity was detected in extracts of external hyphae and mycorrhizal roots. Activity was dependent on exogenous polyP and Mg2+, the reaction product being a long chain polyP. Exopolyphosphatase activity was detected in both mycorrhizal and non‐mycorrhizal roots but activity was 134°O greater in the former. Endopolyphosphatase activity was also greater in mycorrhizal roots. Polyphosphatases were detected in extracts of internal hyphae, but not external hyphae. Polyphosphate glucokinase activity was demonstrated in extracts of external hyphae and mycorrhizal roots, the immediate reaction product being glucose‐6‐phosphate. These results are discussed in relation to potential mechanisms of P translocation and transfer in vesicular‐arbuscular (VA) mycorrhizas. A novel technique for isolating the internal hyphae and associated vesicles and arbuscules from mycorrhizal onion roots is described.
ORIGIN AND EARLY GROWTH OF CELERY EMBRYOIDS
Authors: DUNSTAN D. I. , SHORT K. C. , MERRICK M. A. , COLLIN H. A.
Published: May 2006

Suspension cultures of celery embryoids were initiated by transferring portions of differentiating callus to liquid medium. Light microscope studies of the cells and embryogenic aggregates in the suspensions suggested that the embryoids arose from either single cells within the embryogenic aggregates, when the developing embryoid remained attached to the clump until the globular stage, or from free floating small groups of cells. Both types of development showed the celery embryoids to be of single cell origin. When the embryoid suspension was filtered to remove the larger embryoids and the small embryogenic aggregates and free floating embryoids were mixed with agar and plated, the development of the embryoids depended on the initial inoculum density. At low density further embryoid development was delayed while at the high inoculum density the embryoids became green and grew rapidly into torpedo embryoids with cotyledon leaves and roots. At this stage they could be transferred to a simple inorganic medium to develop into plantlets. The effect of inoculum density was thought to be due to a conditioning effect of the environment. It is suggested that the differentiating units in the embryoid suspension could be used in a cell selection procedure.
THE GROWTH FRACTION OF THE QUIESCENT CENTRE
Authors: CLOWES F. A. L.
Published: May 2006

Evidence used to support a view that the quiescent centre of roots of Avena sativa, unlike those of other species, has a growth fraction of unity, i.e. all its cells are cycling, has been examined in the light of further investigations. Measurement of potential cell‐doubling times before and during a period of DNA labelling by tritiated thymidine in the quiescent centre and in the surrounding meristem show that there is no reason to reject the notion that many cells of the quiescent centre are out of cycle. Observations on planes of division in the proximal tier of the root cap, which were also used to support belief in a fundamental difference in cell kinetics between Avena and other species are also interpreted differently as a result of additional work.
PROTEIN FORMATION IN DEVELOPING SOYBEAN (GLYCINE MAX L. MERR.) SEEDS AND ITS RESISTANCE TO WATER STRESS
Authors: DOVE LEWIS
Published: May 2006

Storage protein synthesis in soybean (Glycine max L. Merr.) seeds is highly resistant to water stress. Seeds of plants deprived of adequate water for normal growth gained the same amount of storage protein as those of well‐watered controls. Cotyledons isolated from these plants synthesized storage protein when immersed in nutrient solution, or in water, or when stored in dry, sterile containers. These findings imply that a large non‐protein nitrogen reserve exists in seeds which is used to synthesize storage protein during development.
INFLUENCE OF VESICULAR‐ARBUSCULAR MYCORRHIZAE ON WATER MOVEMENT THROUGH BOUTELOUA GRACILIS (H.B.K.) LAG EX STEUD*
Authors: ALLEN MICHAEL F.
Published: May 2006

Root growth characteristics and water transport were compared between non‐mycorrhizal Bouteloua gracilis and vesicular–arbuscular mycorrhizal Bouteloua gracilis infected with Glomus fasciculatus. Mycorrhizal plants did not have significantly different leaf area or root length from non‐mycorrhizal plants, but did have significantly fewer and shorter root hairs. Mycorrhizal plants had 50% lower leaf resistance with no change in leaf or root water potentials; thus transpiration was increased 100% with a 50% reduction in whole‐plant, soil‐to‐root and root‐to‐leaf resistance. Assuming that the difference in water uptake was due to transport via the mycorrhizal hyphae, estimated fungus‐to‐root transport was 2.8 × 10−5 mg s−1 per hyphal entry point which compares favourably with evapotranspiration rates measured in other coenocytic fungi. Thus, one of the major factors causing increased water transport and reduced resistance to water through‐flow with mycorrhizal infection may be the increased surface area provided by the hyphae.
DEVELOPMENT OF MYCORRHIZAE, EXTRAMATRICAL MYCELIUM AND SCLEROTIA ON PINUS STROBUS SEEDLINGS
Authors: PICHÉ YVES , FORTIN J. ANDRE
Published: May 2006

On Pinus strobus seedlings cultured in growth pouches successful ectomycorrhiza formation took place upon inoculation with Pisolithus tinctorius, Cenococcum geophilum, Suillus granulatus, Suillus tomentosus, Paxillus involutus, Hebeloma cylindrosporum and Thelephora terrestris.

Under the conditions used ectomycorrhizae formed within 2 weeks and some of them, P. tinctorius, P. involutus and T. terrestris, developed mantles and Hartig nets in less than 5 days. Mycelial strand formation took place around the root system of P. strobus 2 weeks after inoculation with P. tinctorius. Sampling on the 93rd day revealed no difference in ectomycorrhizal formation or the development of mycelial strands and sclerotia between root systems that were or were not illuminated. However, low light intensities on the aerial parts of the seedlings reduced the mycelial strands and sclerotia formation.

Variation of nitrogen and phosphorus concentration added to the pouches were also studied. Increased concentrations of nitrogen, keeping phosphorus constant, led to greener seedlings and increased amount of ectomycorrhizal, mycelial strands and sclerotia. No sclerotia were formed in the complete absence of added nitrogen. Both the percentage of ectomycorrhizal short roots and the phosphorus contents of the seedlings increased in proportion to the amounts of nitrogen added.

Increased concentrations of phosphorus, keeping nitrogen constant, led to a reduction in the percentage of ectomycorrhizal short roots without affecting the nitrogen content of the seedlings, the hyphal strands and sclerotia formation. The observations on the ontogeny of the sclerotia of P. tinctorius reported here for the first time fully support their identity as sclerotia.
A COMPARISON OF THE TOXICITY OF HEAVY METALS, USING ROOT ELONGATION OF RYE GRASS, LOLIUM PERENNE
Authors: WONG M. H. , BRADSHAW A. D.
Published: May 2006

The order of toxicity of different metals affecting root growth of seedlings of rye grass (Lolium perenne S24) was: copper > nickel > manganese > lead > cadmium > zinc > aluminium > mercury > chromium > iron. With the sole exception of manganese, these results confirm those of other studies and the order follows that of the stability of the metallic‐organic complexes. The results are of value in predicting the toxicity of heavy metals in plant growth on contaminated soils.
COMPETITION FOR POLLINATORS IN THE ECOLOGY OF CENTAUREA SCABIOSA L. AND CENTAUREA NIGRA L.
Authors: LACK ANDREW J.
Published: May 2006

The insects which visit Centaurea scabiosa and Centaur̊ea nigra feed mainly on nectar and are likely to visit more frequently the species which produces most nectar. Nectar was extracted from plants in field populations and from plants transplanted into the Botanic Garden, to determine diurnal pattern and total quantity and concentration of nectar produced over 24 h periods.

Florets of both species open in the morning and secrete nectar fairly constantly through the first day of floret opening. C. scabiosa florets continue to secrete into the second day when more florets start to open, but C. nigra usually ceases to secrete nectar around 18.00 h on the first day. C. scabiosa at all times produced more nectar than C. nigra, and on average produced about four times as much. On Hod Hill plants of C. scabiosa produced slightly more nectar than those on the Devil's Ditch. There was no difference between different C. nigra populations. Different plants within each population differed considerably, one plant producing up to six times as much as another under fairly uniform conditions. Less nectar was secreted in cool weather or on a cloudy day than on a warm sunny day, and capitula on shaded shoots produced less than those in the sun. Capitula produced at the beginning and end of the flowering season appeared to secrete less than those produced in the middle. There was a large difference between years in some plants and plants studied in August 1977 produced more than those studied at any other time.
EFFECTS OF SIMULATED ACIDIC RAIN ON YIELDS OF FIELD‐GROWN CROPS
Authors: EVANS LANCE S. , LEWIN KEITH F. , CUNNINGHAM ELIZABETH A. , PATTI MITCHELL J.
Published: May 2006

Experiments were performed to determine the effects of simulated acidic rainfall on yields of radish (Raphanus sativa L.), garden beet (Beta vulgaris L.), kidney bean (Phaseolus vulgaris L.), and alfalfa (Medicago sativa L.) grown under standard agronomic practices. The experimental design allowed the detection of statistically significant differences among means that differed from each other by less than 10 %. The plants were exposed to small additions of simulated rain at pH levels of 5.7, 4.0, 3.1 and 2.7. The spray‐to‐wet simulated rain applications were similar in volume to the median of all ambient rainfall showers. Some plants received no simulated rainfall and all were exposed to ambient rainfall at Brookhaven National Laboratory (Upton, N.Y), which had a mean weighted pH of 4.06 during the summer of 1980. Root mass of radish was not significantly affected by simulated acidic rainfall. The absence of a decrease in root yields in radish was coincident with an absence of visible foliar injury. Beet plants treated with simulated rain applications of pH 4.0, 3.1 and 2.7 showed significant decreases in yield compared with yields under both the ambient rainfall only and pH 5.7 simulated rain treatments. Root yields of beet exposed to simulated rain at pH 5.7, 4.0. 3.1 and 2.7 were 110, 79, 84 and 86% of those receiving ambient rainfall only. Foliar injury on beet was attributed to exposure both to simulated acidic rain of pH 4.0, 3.1 and 2.7 and to several consecutive ambient rainfalls which had an average pH of 3.9. This is the first experiment showing visible foliar injury due to either ambient rainfalls or simulated rain above pH 3.1 under agronomic conditions. With kidney bean, there were no significant differences among treatments of such parameters as number of seeds per plant, mass of seeds per plant and number of pods per plant. There were also no significant differences among treatments for fresh mass or dry mass of alfalfa hay. These studies suggest that no generalizations about crop sensitivity with regard to either plant portion harvested (e.g. roots, fruits, leaves) or taxonomic considerations can be made at the present time.
RESOURCE ALLOCATION ON DWARF SHOOTS OF BIRCH (BETULA PENDULA): REPRODUCTION AND LEAF GROWTH
Authors: TUOMI JUHA , NIEMELÄ PEKKA , MANNILA RAUNO
Published: May 2006

A hypothesis that the female catkin and leaves on the same dwarf shoot of birch compete for the same limited resources of the bud during their development has been tested with Betula pendula. In all trees studied the mean length of leaves, both in May and July, was 15 to 20% lower on reproductive dwarf shoots with a female catkin than on non‐reproductive dwarf shoots of the same tree. However, there were no significant differences in leaf number or in bud development. The idea of plants as metapopulations and the cost of reproduction in trees are discussed.
GROWTH AND REPRODUCTIVE STRATEGIES OF TWO ANNUAL WEEDS AS AFFECTED BY SOIL NITROGEN AND DENSITY LEVELS
Authors: TRIVEDI S. , TRIPATHI R. S.
Published: May 2006

The growth and reproductive strategies of two weeds, Spergula arvensis L., a weed of croplands, and Plantago major L., a weed of wastelands and lawns, were studied in relation to two soil nitrogen and four population density levels. The dry matter yield under the various treatments revealed that S. arvensis is less sensitive to density increase than P. major. The dry matter allocation pattern with reference to reproductive allocation was, however, not appreciably modified by soil nitrogen or density levels in either of the species, though reproductive allocation was higher in S. arvensis than P. major. S. arvensis produced larger numbers of seeds in nitrogen‐rich soil while P. major did not. The results indicate that S. arvensis is more of an ‘r‐’ strategist and P. major is ‘K‐’ selected in the r‐K continuum. In the C‐S‐R strategy model (sensu Grime), P. major may be assigned a position more towards ‘C’ and S. arvensis more towards ‘R’.
INFLUENCE OF AGAR AND SUCROSE ON THE BEHAVIOUR OF DORMANT APPLE EMBRYOS CULTURED IN VITRO
Authors: BARTHE PH. , BULARD C.
Published: May 2006

Dormant as well as completely after‐ripened embryos of Pyrus malus L. var. Golden Delicious were cultured aseptically on media of different compositions. Distilled water was used as the simplest medium. The influence of the addition of agar (8 g 1−1), of mineral substances (macro‐and micro‐elements of the Heller's medium) and of sucrose (10 or 20 g 1−1) was studied. On the agar‐solidified media, three different modes of culture were used, depending upon the nature of the contact between the embryo and the medium. The criteria used to evaluate the depth of dormancy were the germination percentages and the progression in the greening of the cotyledons.

Completely after‐ripened embryos behaved similarly on all the media used whatever the mode of culture. Dormant embryos behaved differently depending upon the composition of the medium and of the mode of culture. Dormancy was always deeper on agar‐solidified media than on liquid media and in the presence of sucrose than in its absence.

In order to determine whether these differences in behaviour were due to quantitative differences in the leaching of free abscisic acid (ABA) into the medium, a two‐step culture method was introduced, using [14C]ABA. Dormant embryos were cultured first on water‐agar containing 10−5 M (±) [2‐14C]ABA (355 KBq μmol−1), then on one of the following media deprived of ABA: water‐sucrose‐agar, water‐agar, water.

Observations during the first culture indicated that the amount of [14C]ABA absorbed was partially metabolized after only 2 days of uptake. During the course of the second culture, part of the original radioactivity of the embryos (4 days [14C]ABA uptake) was released into the medium. Leaching was much greater and lasted longer on water than on media solidified with agar: it does not depend upon the volume of the liquid used (3 or 15 ml). The presence of sucrose (20 g 1−1) in the agar medium does not modify the amounts of 14C‐radioactivity released. The main part of the radioactivity released in water and in water‐agar was shown to be ABA.
CYTOGENETICS OF GALINSOGA PARVIFLORA CAV. AND G. CILIATA (RAF.) BLAKE, AND THEIR NATURAL HYBRIDS (ASTERACEAE)
Authors: GOPINATHAN M. C. , BABU C. R.
Published: May 2006

The somatic and meiotic chromosomes of four natural populations of Galinsoga Ruiz & Pav. ‐ Population I (G. parviflora Cav.), Population II [G. ciliata (Raf.) Blake], Population III and Population IV have been analyzed. Our studies show that G. parviflora is a diploid (2n= 16); G. ciliata is a segmental allotetraploid (2n= 32); Population III is a triploid natural hybrid between G. parviflora and G. ciliata (3n= 24); and population IV is a putative introgressant between G. parviflora and the natural triploid hybrid (2n= 16). The meiotic chromosomes form eight bivalents and do not reveal any irregularities in G. parviflora which shows 100% pollen viability. During the meiosis of G. ciliata, however, 16 bivalents with occasional quadrivalents, anaphasic bridges and laggards are noticed, and pollen viability varies from 90 to 100%. In the triploid hybrids all the 24 chromosomes form univalents which are grouped into an unanalyzable chromosomal entanglement at metaphase I; consequently the per cent pollen viability is 0. The meiotic behaviour of chromosomes in introgressant is similar to that of G. parviflora, except for the high frequency of quadrivalents and laggards, and lesser pollen viability. The presence of inversion loops in G. ciliata and in Population IV imply that the parental species differ in chromosomal rearrangements.
POLYPLOIDY IN THE VICIA SATIVA AGGREGATE
Authors: LADIZINSKY G. , SHEFER Y.
Published: May 2006

Polyploidy is rare in the genus Vicia and is absent in the Vicia sativa aggregate which is composed of types with 2n= 10, 2n= 12 and 2n= 14. Spontaneous amphidiploids were selected among 2n= 10 × 2n= 14 and 2n= 12 × 2n= 14 hybrid derivatives. Chromosome association at meiosis was mainly as bivalents in these amphidiploids; occasionally they were heteromorphic. The spontaneous amphidiploids were inferior to their diploid parental lines in growth rate, vigour and seed set over three generations. The behaviour of the spontaneous amphidiploids was compared with artificially induced autotetraploids. Meiosis in the autotetraploids was characterized by a lower number of associations per chromosome and small number of multivalents. The growth rate of the autotetraploids was retarded and seed set was lower in comparison with the diploid lines. The diploid and the autotetraploid lines could be easily separated from one another by the shape of their pollen grains; elliptical in the diploid plants and tetrahedral in the autotetraploids. No such modification of the pollen grains was observed in amphidiploids. The potential for polyploidy in Vicia sativa and possible reasons for its absence in that aggregate are discussed.
PHYSIOLOGY OF SALT EXCRETION IN THE MANGROVEAVICENNIA MARINA(FORSK.) VIERH
Authors: DRENNAN PHILIPPA , PAMMENTER N. W.
Published: May 2006

Summary

Diurnal and long‐term excretion by leaves ofAvicennia marinaseedlings growing in aqueous culture was correlated with substrate salinity and transpiration. Excretion was greater in 100% than 50% seawater but the reverse was true for transpiration. The diurnal excretion pattern, with exudation minimal during the day and maximal during the night, showed a negative correlation with the daily transpiration pattern. The total amount of salt excreted, however, showed a positive correlation with the total amount of water transpired. Root and xylem sap salinities were linearly related to substrate salinity but leaf Na+increased to a maximum, indicating that control of leaf salt content is at the foliar, rather than the root level.
INDUCTION OF FLOWERING IN WILD LETTUCE (LACTUCA SERRIOLA L.)
Authors: PRINCE S. D. , MARKS M. K.
Published: May 2006

Summary

A comparison of the phenology of plants grown from buried seeds recovered at monthly intervals with plants grown from non‐vernalized and from artificially vernalized seeds showed that seeds which germinate in the field before mid‐summer are hastened in their development and are therefore able to complete their life‐cycles before the end of the growing season whereas those which germinate after mid‐summer are devernalized and therefore remain vegetative until the following growing season. This appears to be the first time it has been suggested that devernalization might play an adaptive role in plants in the natural environment.
THE DEVELOPMENT OF ENDOMYCORRHIZAL ROOT SYSTEMS
Authors: BUWALDA J. G. , ROSS G. J. S. , STRIBLEY D. P. , TINKER P. B.
Published: May 2006

Summary

We have modelled the spread of vesicular‐arbuscular mycorrhizas (VAM) from localized inoculum in a developing root system by assuming that the rate of spread of infection at a particular time is proportional to the product of the length of root already infected and the fraction of the total root which is susceptible to infection at that time. An important parameter of the model is its asymptote n, the maximum fraction of the root system which becomes mycorrhizal. Our model is formally similar to the logistic equation for growth.

An earlier model by Tinker (1975), which predicts that rate of spread of infection would be enhanced by increased density of roots L, (cm cm −3), was compared with ours, using results of experiments on wheat and clover sown at three densities. The new model fitted the data for spread of infection much better, especially that of young infections. The relative rates were generally little altered by total length of roots, Lt, but the absolute values for the two hosts differed widely. This suggests that infection spreads primarily along roots, rather than by random contact between roots and hyphae. This type of model may be useful for exploring the mechanisms by which environmental changes affect spread of vesicular‐arbuscular mycorrhizas.
INTERACTION OF LIGHT INTENSITY AND SOIL TEMPERATURE WITH PHOSPHORUS INHIBITION OF VESICULAR‐ARBUSCULAR MYCORRHIZA FORMATION
Authors: GRAHAM J. H. , LEONARD R. T. , MENGE J. A.
Published: May 2006

Summary

The interaction between light intensity and soil temperature with phosphorus inhibition of vesicular‐arbuscular mycorrhiza (VAM) formation in sudangrass (Sorghum vulgare, Pers.) was investigated in P‐deficient (0.5 mg P kg−1) sandy soil amended with 0 (OP), 15 (15P) and 30 (30P) mg P kg−1 soil as superphosphate. For seedlings inoculated with Glomus fasciculatus and grown at 100, 75, and 50% of glasshouse light intensity, the reduction in VAM formation by added soil P (15 P and 30P) was greatest at the lower light levels, whereas in the OP treatment, VAM formation was unaffected by a decrease in light intensity. Increases in root P concentration resulted from both soil P amendment and, in the 15P treatment, from a decrease in light intensity, and were associated with decreases in root membrane permeability and corresponding decreases in root exudation of amino acids and sugars. The reduction in sugar exudation in the 15P treatment at lower light intensity was paralleled by a decrease in root extract levels of sugars, but decreases in amino acid exudation could not be explained by changes in amino acid levels in root extracts. These results suggest that P inhibition of VAM formation is more severe at lower light intensities because of a decrease in membrane‐mediated exudation, although a reduction in sugar levels in root cells may also contribute to the observed decrease in exudation.

When inoculated seedlings were grown at 25, 30, and 35°C soil temperatures, the reduction in VAM formation in the 15P and 30P treatments was overcome by increase in soil temperature. The increase in VAM formation by increased temperature in the 15P plants was associated with significant increases in root membrane permeability and exudation without a corresponding change in root P concentration. In the OP treatment, an increase in soil temperature increased VAM formation with little effect on root exudation, which suggested an effect of temperature on Glomus fasciculatus. Higher soil temperature may increase VAM formation through either a direct effect of temperature on the fungus or an indirect effect via an increase in leakage of root metabolites necessary for fungal activity, or both.
CHANGES IN ABSCISIC ACID LEVELS DURING AFTER‐RIPENING AND GERMINATION OF ACER PLATANOIDES L. SEEDS
Authors: TILLBERG E. , PINFIELD N. J.
Published: May 2006

Changes in abscisic acid (ABA) levels during after‐ripening and germination of embryos of Acer platanoides have been studied by gas liquid chromatography. Inductive low temperature after‐ripening caused a very large decline in ABA content of the embryos over a 131‐day period, although small amounts remained even after this time. Reductions were also observed in control samples maintained at 17 °C but these were much smaller. During germination, following an inductive chilling treatment of 60 days, the levels of ABA in the embryos remained low throughout a 72 h incubation period. There was, however, a transient increase after 24 h, which was attributed to stress.

The common concept that endogenous ABA plays a role in the regulation of dormancy seems valid for seeds of A. platanoides and the results are discussed in terms of the overall promotor/inhibitor balance within the seed. ABA, however, does not seem to be directly involved in regulation of the germination process.
THE INFLUENCE OF LIGHT INTENSITY AND ARTIFICALLY EXTENDED PHOTOPERIOD UPON INFECTION AND SPORULATION OF GLOMUS FASCICULATUS ON SUDAN GRASS AND ON ROOT EXUDATION OF SUDAN GRASS
Authors: FERGUSON J. J. , MENGE J. A.
Published: May 2006

Mycorrhizal inoculum of Glomus faciculatus, as measured by root infection and sporulation on sudan grass, increased with increasing light intensity. Compared to natural glasshouse daylight, spore numbers of G. fasciculatus also increased dramatically when mycorrhizal sudan grass was exposed to extended photoperiods with mercury vapour or metal halide lamps of high intensity. Results from both light experiments indicate that the level of sugars, but not amino acids, in root exudates from 2‐month‐old sudan grass plants was correlated with the spore production of G. fasciculatus. It appears that growing sudan grass at greater light intensities and under extended photoperiods will increase the quantity and quality of commercial G. fasciculatus inoculum.
AN ULTRASTRUCTURAL ANALYSIS OF THE DEVELOPMENT OF MYCORRHIZAS IN MONOTROPA HYPOPITYS L.
Authors: DUDDRIDGE J. A. , READ D. J.
Published: May 2006

The ultrastructural differentiation of mycorrhizas of the achlorophyllous plant Monotropa hypopitys was examined in relation to the stages of growth of the shoot. Plants were collected at regular intervals during the growing season and their roots were immediately excised and prepared for scanning and transmission electron microscopy. In addition to the presence of a fungal sheath and Hartig net of similar structure to those seen in ectomycorrhizas, the outer cortical cells frequently contain characteristic fungal intrusions. While not breaching the host cell wall, these intrusions stimulate its invagination. The resulting structures, analogous to the transfer cells found in regions of intensive solute mobilization and transport, are produced in greatest numbers during the period of most rapid shoot extension. The relationship between their structure and possible function is discussed. The structure of mycorrhizas in Monotropa hypopitys is sufficiently distinct from that of arbutoid mycorrhizas, to warrant the creation of a new category which we term ‘monotropoid’.
VARIATIONS IN NITROGENASE ACTIVITY AMONG PURE‐CULTURED FRANKIA STRAINS TESTED ON ACTINORHIZAL PLANTS AS AN INDICATION OF SYMBIOTIC COMPATIBILITY
Authors: DILLON J. T. , BAKER D.
Published: May 2006

Frankia strains ArI5, AvcIl, AvsI2, CpI1 and MpI1, previously isolated from nodules of actinorhizal plants, were tested in association with various actinorhizal plants to determine differences in nitrogen‐fixing effectiveness. Alnus incana ssp. rugosa, Alnus rubra, Alnus viridis ssp. crispa, Comptonia peregrina and Myrica gale plants, grown in nitrogen‐free water culture, were inoculated with the cultured Frankia strains. Significant differences in rates of acetylene reduction were found among strains which suggested that endophytes were not fully compatible with some or all of the host plants tested. A pattern of compatibilities among hosts and endophytes was developed to explain differences in rates of acetylene reduction.