bluuebunny/crossref_metadata_2025 huggingface dataset:
SOME OBSERVATIONS ON THE SIZE AND SHAPE OF LICHEN ASCOSPORES IN RELATION TO ECOLOGY AND TAXONOMY
Authors: PENTECOST ALLAN
Published: May 2006

Summary

The length, breadth and volume of a large sample of ascospores from lichenized and non‐lichenized ascomycetes were compared and found to be approximately log‐normally distributed. Lichen ascospores were also classified into sizes and types and their distribution in relation to the substratum colonized was analyzed using x2. The distributions were found to be heterogeneous with certain spore types and sizes more frequent on some substrata than others. These results are discussed with reference to the survival, germination and atmospheric dispersal of ascospores.

Ascospore length and breadth was measured in a single plant of Opegrapha chevallieri Leight. (Loculoascomycetes) and found to be normally distributed. Taxonomic implications are considered.
ULTRASTRUCTURE OF THE ENVELOPE OF CODIUM A USTRALICUM (SILVA) CHLOROPLASTS IN THE ALGA AND AFTER ACQUISITION BY ELYSIA MAORIA (POWELL)
Authors: BRANDLEY BRIAN K.
Published: May 2006

Summary

Four fracture faces of Codium australicum (Silva) chloroplast envelopes are characterized in the alga and after incorporation into Elysia maoria (Powell). The outer membrane generally has a lower density of particles than the inner in both alga and animal. Both inner and outer envelope faces in the animal are significantly different to those in the alga in terms of particle size distributions. The outer envelope also differs in terms of particle densities. No evidence was found for a phagosome membrane surrounding the chloroplast in the animal. The chloroplast surface area is the same in the alga and in the animal, but the plastid volume increases in the animal. Changes in the envelope membranes may be related to functional aspects of the chloroplast‐sacoglossan association.
AN UNUSUAL HETEROMORPHIC INCOMPATIBILITY SYSTEM
Authors: PHILIPP M. , SCHOU O.
Published: May 2006

Summary

Based on measurements of floral parts and experiments, Anchusa officinalis L. is shown to have a distylous breeding system. Dimorphism is found in the style length/anther height ratio, in stigma morphology and in pollen and corolla size. Plants are self‐incompatible but intra‐ and intermorph compatible. Long‐styled plants outnumbered short‐styled in all populations. Stigmas in short‐styled flowers receive a larger quantity of pollen than those of long‐styled.
AN INVESTIGATION INTO THE USE OF THE ‘‐DEME’ TERMINOLOGY
Authors: BRIGGS D. , BLOCK M.
Published: May 2006

Summary

The ‘‐deme’ terminology was coined by Gilmour and associates to bring order to the confusion of terms used for classifying plants at or below the species level.

During the past decade details of key‐words in titles and abstracts of scientific papers have been stored in computer data banks. Using an on‐line system in a search of five data bases, an estimate of the use of the ‘‐deme’ and other technical terms has been made. We have discovered, in a search of nearly 8 million papers, that the ‘‐deme’ terminology has rarely been used by biologists (only 115 uses). Moreover in 74% of cases the terminology has not been employed in accordance with the intentions of its authors, the term ‘‐deme’ being incorrectly used to denote ‘a local interbreeding population’. The use of various terms in describing variation, at and below the species level, is discussed.
COMPARISON OF THE ONION PLANT (ALLIUM CEPA) AND ONION TISSUE CULTURE
Authors: TURNBULL A. , GALPIN I. J. , SMITH J. L. , COLLIN H. A.
Published: May 2006

Tissue cultures of onion, differentiated into roots and shoots, were examined for total flavour precursor levels, composition of the flavour precursors and activity of the enzyme alliinase. Comparisons were made with undifferentiated callus and with the roots and shoots of germinating seedlings and shooting bulbs.

Undifferentiated callus contained none of the major flavour precursor compound, 5‐trans‐prop‐1‐enyl‐L‐cysteine sulphoxide, but in the differentiated tissue this compound was present in both redifferentiated roots and shoots. In intact plants, more flavour precursor accumulated in rapidly growing roots and shoots.

Onion bulb tissue and callus tissue from a long established cell clone and a newly initiated clone were examined under the electron microscope. The major structural component in the onion bulb cells, which was absent in the callus, was a larger number of vesicles in the cytoplasm and central vacuole. Since callus does not produce the onion flavour precursor compounds, possibly, in normal onion tissue, the vesicles are part of the flavour producing system, either as a store for the flavour precursors or for the degradative enzyme alliinase; in this way both parts of the system may be spatially separated until the tissue is damaged or cut.
THE DIFFERENTIAL ABILITY OF AQUATIC PLANTS TO UTILIZE THE INORGANIC CARBON SUPPLY IN FRESH WATERS
Authors: ALLEN E. D. , SPENCE D. H. N.
Published: May 2006

The photosynthetic activity of 15 species of microalgae and macrophytes was measured by continuous recording of oxygen concentration, and/or the change in pH, in bathing solutions of known alkalinity and carbon concentration. The microalgae had considerably greater apparent affinities for HCO3− and slightly greater apparent affinities for CO2, than the macrophytes (including several previously established HCO3‐users), while the macrophytes had larger apparent affinities for CO2 than for HCO3− and larger diffusive resistances to CO2. For species with different affinities for CO2 and HCO3−, assimilation rate in a solution of constant alkalinity showed a distinct reduction when the CO2 concentration decreased to a value typical of each species; a list of such ‘CO2 compensation points’ is presented. (The same CO2 compensation point was obtained for Elodea canadensis by extrapolation of rate‐substrate curves in solutions of which the pH was varied at each of three constant total carbon concentrations). At still lower total carbon values, any assimilation was held to be due to HCO3− uptake, and HCO3− compensation points for some species are given. Rather than ‘users’ and ‘non‐users’ of HCO3− it is concluded that a gradation exists, use depending on HCO3− as affected by alkalinity and pH of the bathing solution, and on the species' HCO3‐compensation point. Natural rates of photosynthesis of macrophytes and some microalgae are usually functions of exogenous [CO2] while those of other microalgae are functions of [CO2] and [HCO3−], with competitive effects at high pH in solutions of prevailingly low alkalinity. In characterizing the response of aquatic plants to inorganic carbon supply, a knowledge of CO2 and HCO3− compensation points is therefore essential.
FUNGAL GROWTH IN A LATTICE: A TENTATIVE EXPLANATION FOR THE SHAPE OF DIAMOND‐CANKERS IN SYCAMORE
Authors: RAYNER A. D. M. , BEVERCOMBE G. P. , BROWN T. C. , ROBINSON A.
Published: May 2006

The characteristic shape of diamond‐cankers in sycamore may be attributable to spread of fungal infection via the medullary rays. The rays become densely filled with fungal hyphae in infected bark, and when viewed tangentially are arranged in a lattice‐like array with angles between the diagonal rows similar to the apical and side angles of diamond‐cankers observed in the field. Computer simulation has shown how a range of types of random growth processes could result in diamond‐shaped patterns if a fungus spread through such a lattice, with each ray serving as a centre from which its neighbours could become occupied and act in turn as centres.
ECOLOGICALLY‐LINKED VARIATION IN MORPHOLOGY, ACETYLENE REDUCTION, AND WATER RELATIONS IN PSEUDOCYPHELLARIA DISSIMILIS
Authors: SNELGAR W. P. , GREEN T. G. A.
Published: May 2006

Pseudocyphellaria dissimilis (Nyl.) D. Gall and P. James in litt populations were shown to possess different morphologies which correlated with the evaporative demand of their environment. The variations in morphology consisted of increased thallus thickness, mostly from increased medulla thickness, and increased rhizine length in the more exposed population. These changes confer a decreased surface/volume ratio and increased water storage in the form of external water that could be removed by blotting but not shaking. A consequence of these changes was a slower drying down rate. No differences in water loss rate per unit area were found between populations indicating that no morphological modifications exist to decrease water loss. Preliminary work on the acetylene reduction rates of the populations demonstrated a considerable difference in rates between the individual populations' and indicated that acetylene reduction could be another useful indicator of physiological adaptation.
THE EXPLOSIVE RELEASE OF POLLEN IN FLOWERS OFHYPTIS(LAMIACEAE)
Authors: BRANTJES N. B. M. , DE VOS O. C.
Published: May 2006

The Brazilian speciesHyptis paulianaEpling probably has an ornithopilous flower, in which explosive pollen presentation is effected by the sudden release of the stamens from a petal lobe, called a carina. Two hinges are situated in the suspensor of this carina. Pressure in large epidermal cells of the suspensor, in combination with the stiffness of collenchymatic, deeper cell layers, produces the force for the explosion. Shortly before anthesis the filaments elongate so that the stamens enter deep into the carina. At anthesis two hinges in the suspensor plate unfold and the stamens keep the carina in this excitable position. A disturbance causes the anthers to slip from the carina, which then can flip back, while the anthers swing up and eject the pollen on to the flower visitor. In the receptive phase the stamens bend down and the style elongates. In the Lamiaceae, subfamily Ocimoideae, it seems likely that an explosive mechanism has evolved at least twice.
EXPERIMENTAL STUDIES ON THE DISTRIBUTION OF THE SEXES OF MERCURIALIS PERENNIS L.
Authors: WADE K. M.
Published: May 2006

(1) Populations of flowering male and female shoots of Mercurialis perennis were grown in three experiments under different light screens: (i) the sexes grown together in a replacement series under a screen transmitting 11 % incident light; (ii) the density of the plants varied under an 11 % light screen; and (iii) the sexes grown separately with Holcus mollis under light screens transmitting 31 % and 2% incident light.

(2) In the replacement series with mixed sexes, the males grew more than the females at (male:female) 10:10 while the females grew more at 17:3 and 3:17. The sexes grew similarly in monoculture. The results for total yield of the plants suggest that competition between the sexes was less than that within them.

(3) In the density experiment, the males grew more than the females as the density increased from 20 to 30 plants/box and both grew similarly at 42 plants/box.

(4) It is suggested that observed uneven sex ratios in natural populations of shoots may be a result of the sexual differences in growth as the density of the plants increases.

(5) In the replacement series with H. mollis under the 31 % light screens the males grew more than the females at (M. perennis: H. mollis) 3:17 while the females grew more at 17:3. These results suggest that males may persist longer in association with other species.

(6) No consistent results were obtained from the H. mollis replacement series under the 2 % light screens.

(7) The sexes grew similarly more under the 31 % compared to the 11 % light screens, suggesting that neither is physiologically intolerant to increased sunlight.
A STUDY OF THE INTRACELLULAR AND INTERCELLULAR DISTRIBUTION OF THE DATURA STRAMONIUM LECTIN USING AN IMMUNOFLUORESCENT TECHNIQUE
Authors: JEFFREE C. E. , YEOMAN M. M.
Published: May 2006

The intracellular and intercellular distribution of the lectin in seeds, stem and callus of Datura stramonium was visualized by means of an indirect immunofluorescent technique employing antibodies, raised in a rabbit against highly purified lectin obtained from Datura seeds. The lectin was detected in the protoplasts of all cells tested, apparently associated with the plasmalemma and the membranes of cell organelles. Cell walls appear to be free of lectin. In stems, where lectin concentrations are very low, epidermis, endodermis and phloem are the richest sources. The significance of the distribution of the D. stramonium lectin is discussed in relation to the possible functions of this molecule.
PHYSIOLOGICAL INTERACTIONS DURING THE INITIAL STAGES OF EMBRYOGENESIS IN CULTURES OF DAUCUS CAROTA L.
Authors: WARREN GRAHAM S. , FOWLER MICHAEL W.
Published: May 2006

Somatic globular embryos of carrot develop abnormally when transferred at low density to fresh, minus‐auxin medium, whereas normal development ensues after transfer to conditioned medium, or to fresh medium at high densities. It is suggested that a critical level of an ‘embryo factor’ is required to co‐ordinate cell division and morphogenesis. Embryo death occurs after the heart stage in minus‐auxin cultures of low embryogenic potential. This behaviour may result from the production of auxin as these cultures show some plus‐auxin characteristics. The decline in the capacity for normal embryogenesis which often accompanies repeated subculture is suggested to result, in part, from a combination of these factors.
ORIGIN OF REDUCTANT FOR REDUCTION OF NITRATE AND NITRITE IN RICE AND WHEAT LEAVES IN VIVO
Authors: RAMARAO C. S. , SRINIVASAN  , NAIK M. S.
Published: May 2006

Malonate inhibited completely anaerobic dark reduction of nitrate in rice leaves and the inhibition was reversed by fumarate. Under dark anaerobic conditions l4CO2 evolution from endogenously labelled substrates was dependent on nitrate reduction. When nitrate reduction was inhibited by tungstate or cyanide, 14CO2 evolution was inhibited and conversely, when 14CO2 evolution via the citric acid cycle was inhibited by malonate, nitrate reduction was inhibited. These results suggest a mitochondrial origin of NADH for nitrate reduction and this suggestion was confirmed by following the evolution of 14CO2 from endogenous substrates, mostly organic acids, labelled in darkness. In comparison with the reduction of nitrite in light, the dark aerobic reduction of accumulated nitrite was very slow and commenced only after a time lag of 20 min. This could be a detoxification mechanism for the removal of nitrite which does not normally accumulate in the leaves under natural conditions. NADH acted as a physiological reductant for dark aerobic nitrite reduction.
ULTRASTRUCTURE AND ELECTRON‐PROBE MICROANALYSIS OF THE METACHROMATIC VACUOLAR GRANULES OCCURRING IN TAXUS MYCORRHIZAS
Authors: STRULLU D. G. , GOURRET J. P. , GARREC J. P. , FOURCY A.
Published: May 2006

Numerous metachromatic vacuolar granules occur in the hyphae of the fungal symbiont of Taxus baccata mycorrhizas. These granules exist in the trunks and in proliferating arbuscules but they are absent in lysed arbuscules. Direct microanalysis with an electron probe shows that they have a high phosphorus and calcium content. Potassium and magnesium are also present but in lesser quantities. The concentration of phosphorus and calcium is higher in the granules than in the light part of the vacuoles. The concentration of phosphorus also is higher in the granules than in the nuclei of the root cells and the concentrations of calcium are greater than those measured in the pecto‐cellulosic wall of root cells. The role of calcium in the metabolism of phosphorus within the tissues of mycorrhizas still remains unknown.
CELL PROLIFERATION IN ECTOTROPHIC MYCORRHIZAS OF FAGUS SYLVATICA L.
Authors: CLOWES F. A. L.
Published: May 2006

The organization of the meristem and rates of cell proliferation in its regions have been investigated by continuous labelling of DNA and stathmokinetic experiments. Mycorrhizas bearing intact fungal sheaths and those in which the apices had grown through the sheaths were compared with uninfected roots.

Despite low overall rates of mitosis the restricted meristems of mycorrhizal roots have quiescent centres of non‐cycling cells, the numbers of which fluctuate periodically. At one time the quiescent centre may comprise only the cells at the pole of the stele, at others these plus from one to seven tiers of axial cells belonging to the cortical complex distal to the stelar pole. This flux in cell cycling forces an exchange in roles between cortical cells and cap initials which produces further changes in the organization of planes and rates of cell division.

Roots which have escaped from the fungal sheath have higher rates of mitosis and larger meristems than those with intact sheaths, but the cap meristems of the latter contribute over a quarter of the total production of cells by the whole apex compared with a much smaller fraction in escaped roots. The fungal sheath must therefore contend with the production of as many as 50 cap cells per day and this problem is discussed.
EFFECT OF CALCIUM ON THE UPTAKE AND TOXICITY OF LEAD IN HORDEUM VULGARE L. AND FESTUCA OVINA L.
Authors: GARLAND C. J. , WILKINS D. A.
Published: May 2006

The effect of increasing calcium concentration on root growth and the uptake of lead from solutions of lead nitrate, by both barley seedlings and lead‐tolerant and non‐tolerant plants of Festuca ovina, are described. Lead uptake into the roots of all plants declined linearly with the logarithm of increasing calcium nitrate concentration up to 12.72 mM. Root extension growth in each lead solution increased as calcium concentration was raised, and this increase was greater than could be accounted for by the diminishing lead uptake; a second influence of calcium may thus be indicated. The regression of root growth, or tolerance index, on root lead content may be a useful indicator of sensitivity to the metal.
ECO‐PHYSIOLOGICAL ASPECTS OF INTER‐SPECIFIC AND SEASONAL VARIATION IN NITRATE UTILIZATION IN THE GENUS AGROSTIS
Authors: OSBORNE B. A. , WHITTINGTON W. J.
Published: May 2006

Nitrate utilization, as judged by dry matter production and nitrate reductase activity, was examined in species of the genus Agrostis and compared with species of Lolium and Poa. A. setacea had the lowest ability to utilize nitrate which correlated with its restricted ecological distribution in areas of low nitrate availability. In contrast, A. tenuis which may also be found in low nitrate sites, exhibited a higher nitrate reductase activity but lower dry matter production than the species A. stolonifera and L. multiflorum, both of which are characteristic of sites with higher nitrate availability. A high potential to utilize nitrate may be important in low nitrate areas subjected to marked fluctuations in supply. Correlations between nitrate utilization and growth were, in general, non‐significant and often negative. The results suggest that the efficiency of incorporation of reduced nitrogen into plant structure may bring about differences between species in the production of dry matter. Significant variations between species and response to nitrate were found in relation to the time of year. Maximum enzyme activities were found during the winter months with little change, after a drop in activity in the early spring, during the growth period. The peaks in activity found may not represent nitrate utilization but rather the induction of high levels of enzyme with little subsequent reduction of nitrate. Variation in soil pH did not modify the seasonal pattern and had little overall effect on either nitrate utilization or dry matter production although significant differences were found between species in both of these factors.
LONG‐DISTANCE POLLEN IN LATE WISCONSIN QUANTITATIVE ANALYSIS*
Authors: BIRKS H. J. B.
Published: May 2006

In Late Wisconsin sediments of Minnesota there occur fossil pollen and spores of certain taxa that are unlikely on ecological or phytogeographical grounds to have grown in Minnesota at that time. Long‐distance dispersal is believed to be the cause. The occurrences of 21 such types in three sites in Minnesota are analyzed statistically. Contingency‐table analysis suggests that some types occur together more commonly or more rarely than would be expected by chance. Principal co‐ordinates analysis similarly reveals groups of taxa whose pollen commonly occur together in time.

The patterns within the series of occurrences, when viewed as point processes, are characterized by the techniques of statistical analysis of series of events. These analyses show that the series of occurrences ofAcer saccharum, Carya, Celtis occidentalis, Juglans cinerea, Platanus occidentalis, and probablyA. saccharinum‐typeandTilia americanapollen all have statistically significant trend and that their rates of occurrence are higher between 8300 and 10200 B.P.Athyrium filix‐feminaspores show a higher rate of occurrence between 20500 and 12000 B.P. The series of occurrences of all the other pollen types accord with a trend‐free renewal process. The series ofAcer negundo, Iva ciliata‐type, I. xatithifolia‐type, Morus rubra, andSarcobatus vermiculatuspollen are long enough to permit more detailed analysis. All these series appear to reflect a homogeneous Poisson process with random occurrences in time.

Hypotheses to explain these patterns are discussed in terms of migration and population expansion to the south and east of Minnesota and of changing atmospheric circulation patterns during the Late Wisconsin. The need for more detailed series of occurrences is emphasized.
OVULE DEVELOPMENT INORNITHOGALUM CAUDATUM(LILIACEAE) WITH A REVIEW OF SELECTED PAPERS ON ANGIOSPERM REPRODUCTION
Authors: TILTON VARIEN R. , LERSTEN NELS R.
Published: May 2006

Ornithogalumovules are crassinucellate, and the nucellar epidermis forms a nucellar cap which is secretory. The nucellus accommodates archespore and megaspore mother cell expansion by a concurrent increase in its size. It accommodates functional megaspore and megagametophyte expansion by simultaneously undergoing growth and partial degeneration. Nucellar degeneration is centrifugal and appears to be an autolytic process rather than a result of mechanical pressure from the growing megagametophyte. Megagametophyte development is of thePolygonumtype. Mitotic divisions of the functional megaspore and its daughter cells are characterized by a perinuclear distribution of organelles. Some starch is stored in the micropylar end of the nucellus, but the majority is stored in the chalazal end around the hypostase. A strand of cytoplasm extends between the egg apparatus and antipodals. The micropylar polar nucleus moves across the central cell's vacuole in this strand to reach its mate. Antipodals initially are vacuolate but later fill with dense cytoplasm and numerous starch grains. Preliminary evidence from light microscopic investigation indicates a thin layer of wall material surrounds the egg apparatus. However, around the chalazal end of the egg this layer may be disjointed islands of wall material rather than a continuous wall. Synergid cytoplasm contains an abundance of organelles and a large filiform apparatus (FA) projects into it. In addition to the FA, synergid walls have a knobbed ingrowth around their micropylar end. We propose that the antipodals and central cell function initially as storage cells for nutrient reserves and later as nurse cells for embryo and endosperm whereas the synergids function as secretory cells which produce an agent(s) which attracts pollen tubes and, via the filiform apparatus, as cells which receive the pollen tube.
OVULE DEVELOPMENT INORNITHOGALUM CAUDATUM(LILIACEAE) WITH A REVIEW OF SELECTED PAPERS ON ANGIOSPERM REPRODUCTION
Authors: TILTON VARIEN R.
Published: May 2006

The chalazal end of the egg projects beyond the synergids while the micropylar end is in contact with the nucellar epidermis. The egg nucleus and nucleolus are large and, along with most of the cytoplasm, are located chalazally while a large vacuole occupies the micropylar end. The egg cell wall is attenuated chalazally but, based on preliminary light microscope observations, it does appear to surround the entire cell in some cases. The synergids each have a large chalazal vacuole with the majority of their cytoplasm in the micropylar half of the cell. Nuclei and nucleoli are large and other organelles are numerous. Plastids and endoplasmic reticulum (ER) are more numerous chalazally while mitochondria appear to be evenly distributed. Filiform apparatus (FA) formation occurs late in synergid maturation. The FA is large, well developed, and is surrounded by a vacuolate zone. Various sized vesicles with fibrillar or flocculent contents occur within the FA. The FA stains for both protein and RNA in addition to carbohydrate which is the dominant component. The synergid walls have a knobbed ingrowth around the periphery of their micropylar end. Neither egg nor synergids store any metabolites.

This information, coupled with overwhelming evidence from the literature reviewed, has led me to conclude all angiosperm synergids are active in synthesizing and, via the FA, in secreting a substance(s) which influences the final phases of pollen tube growth. Movement of materials into a megagametophyte via the FA seems unlikely, but if it does occur, it is probably an inconsistent feature and only of trivial consequence.
CESSATION OF VASCULAR ACTIVITY CORRELATED WITH APOSPOROUS DEVELOPMENT IN PTERIDIUM AQUILINUM (L.) KUHN
Authors: SHEFFIELD E. , BELL P. R.
Published: May 2006

Apospory has been found to occur on leaves of Pteridium aquilinum still attached to parent plants, although previous work had indicated that detachment was a prerequisite for regeneration. It is clear, however, that such recrudescence occurs only in leaves where active vascular flow has ceased, and which are also in contact with a moist surface. It is proposed that the cessation of an active vascular supply has an inductive effect. The inability of mature fronds to behave aposporously is attributed to the presence of a thick cuticle external to the superficial cells, which is thought to prevent the exchange of metabolites between frond and medium.
THE KEEL PETAL COLOUR POLYMORPHISM OF LOTUS CORNICULATUS L. IN SCOTLAND
Authors: ABBOTT RICHARD J.
Published: May 2006

In a survey of the keel petal colour polymorphism in Lotus corniculatus L. conducted at 61 coastal and inland locations in Scotland, there was a major difference in morph frequency between populations in the west and those in the east and central areas, with the dark keel being at low‐relative frequency at most western locations. When figures for east and central Scotland were considered, there was a slight but statistically significant increase in the dark keel morph with increasing latitude, a pattern which was not found in Scotland as a whole.
THE ELM DECLINE: THE DEPLETION OF A RESOURCE
Authors: GARBETT GEOFFREY G.
Published: May 2006

A high‐resolution pollen diagram of the elm decline at Ellerside Moss, previously studied by Oldfield and Statham (1963), was constructed by freezing the peat core and taking samples at 02 cm intervals using a sledge microtome. Consecutive samples were counted across the most critical part of the diagram.

Ivy pollen was used as an indicator of standing dead trees, but this did not provide any evidence to support the idea that disease was a major factor contributing to the elm decline. The diagram does, however, provide evidence of leaf‐fodder gathering involving elm, oak and lime during the initial stage of the elm decline followed by a period when elm only was exploited. It is argued that this resulted in a near destruction of the elm and thus initiated the partial clearance of the elm‐dominated regions and later the production of small temporary clearances throughout the forest.

Using the available evidence from a number of disciplines an interpretation of the cultural and economic basis of the elm decline is offered in the light of the present findings. It is seen primarily as an over‐exploitation of a resource.
NUTRITIONAL STRATEGIES OF SUBMERGED BENTHIC PLANTS: THE ACQUISITION OF C, N AND P BY RHIZOPHYTES AND HAPTOPHYTES
Authors: RAVEN J. A.
Published: May 2006

Submerged benthic plants (algae and ‘higher plants’) can be classified into two groups on the basis of their attachment to the substrate. ‘Haptophytes’ are attached to the surface of rocks; ‘Rhizophytes’ have rhizoids, roots or rhizomes within the substratum (sand or mud). Haptophytes must obtain all of their nutrients from the bulk water phase, while rhizophytes can obtain some of their nutrients from the sediment. Evidence as to the sites of nutrient uptake on the surface of rhizophytes supports the view that a substantial fraction of phosphorus and nitrogen and, in some cases, inorganic carbon, is obtained from the sediment. This might be expected to make the portion of the rhizophyte which occurs in the bulk water phase more specialized for interception of photosynthetic light and C than the corresponding portion of the haptophyte which also intercepts and absorbs all other mineral nutrients. The morphology of the haptophyte and its frequent occurrence in more rapidly flowing water means that the superficial unstirred layer is less of an impedance to nutrient transport from the bulk medium to the plant surface. This in turn improves the supply of inorganic C, which is reflected in more negative delta 13C values and higher biochemical capacities for photosynthesis per unit plant surface in haptophytes than in rhizophytes. Haptophytes frequently have colourless hairs on their surface, especially in media of low nutrient content or with poor water movement: in many cases, these hairs seem to be involved in nutrient uptake. Despite their different mechanisms for uptake of nutrients, rhizophytes and haptophytes can produce similar biomasses and chlorophyll m−2, although rhizophytes may have rather lower productivities. The role of symbiotic associations (mycorrhizas in vascular plants; microalgae in invertebrates) in uptake of nutrients and photosynthesis is discussed in relation to haptophytic and rhizophytic strategies, as is the evolution of land plants.
AMYLOSE IN FLORIDEAN STARCH
Authors: McCRACKEN D. A. , CAIN J. R.
Published: May 2006

Previous reports, based on studies involving approximately 10 genera of the higher red algae, have concluded that floridean starch is composed of amylopectin only. Our investigations on seven members of the Porphyridiales and a member of the Bangiales (Erythrocladia) have demonstrated conclusively the presence of amylose in red algal starch.
THE OCCURRENCE AND SIGNIFICANCE OF DISPENSABLE PROTEINS IN PLANTS
Authors: ADAMS C. A. , RINNE R. W.
Published: May 2006

Summary

Plants produce many different kinds of proteins. Enzymes, ribosomal proteins and storage proteins have clearly defined, ubiquitous, physiological roles and are indispensable for normal plant growth. Other proteins, such as urease, β‐amylase, lectins, proteinase inhibitors and some proteinases, have a varied distribution and no clear physiological role. These proteins are dispensable in that some plant species manage without them, or with only extremely low levels, whereas other species accumulate significant quantities of the proteins. Dispensable proteins all have defined biological activities, but in most cases these activities do not explain their physiological role. Urease is able to degrade urea, but many seeds contain little or no urea. Beta‐amaylase only attacks gelatinized starch, not intact starch granules. Lectins agglutinate red blood cells. Trypsin inhibitors specifically inhibit a proteolytic enzyme from animals. These proteins may fulfill a non‐specific role as part of the cellular protein complement and therefore could presumably be replaced by other proteins in other species. The production of dispensable proteins may also be another aspect of general plant secondary metabolism which already encompasses the biosynthesis of amino acids, amines, lipids and carbohydrates. Because they are dispensable, these proteins possibly could be manipulated through plant breeding or epigenetic procedures, without accompanying deleterious side effects. The presence of large quantities of these proteins or their absence appears to have little phenotypic effect on a particular species.
PEROXIDASE ISOZYMES IN RELATION TO DEVELOPING WATER DEFICITS IN TWO ZEA MAYS L. CULTIVARS
Authors: THAKUR PARTAP S. , SINGH GURMIT , RAI VINAY K.
Published: May 2006

Summary

Zea mays L. cultivars Agati‐76 and Vijay have been scanned for peroxidase isozyme changes under varying water stress. Water stress did not induce the synthesis of any new isozyme in either cultivar, but one band with low electrophoretic mobility (RF 0·29) disappeared in leaves of the susceptible cv. Vijay. A significant inhibition of enzyme activity on a protein basis was observed in both cultivars, but to a greater extent in the susceptible cultivar, Vijay. Enhanced enzyme activity on a fresh wt basis was recorded in cv. Agati‐76 with increasing stress. Peroxidase activity declined in stressed roots of both cultivars. A highly significant negative correlation was found between enzyme activity and water saturation deficit. The possible physiological role of peroxidase in drought resistance is discussed.
AN EXPERIMENTAL INVESTIGATION OF INHIBITION OF PHYTOPLANKTON PHOTOSYNTHESIS AT LAKE SURFACES
Authors: BELAY AMHA
Published: May 2006

Summary

Photoinhibition of photosynthesis in natural populations of phytoplankton has been investigated in situ in Windermere, English Lake District, and Llyn Padarn, North Wales. The extent of inhibition was found to be directly related to irradiance and to increase with time of exposure. Inhibition was increased when the ultra‐violet component of sunlight was not removed by enclosure of samples in glass bottles. Supersaturation with oxygen to the extent likely to occur in the surface waters of lakes did not appear to be an important factor increasing photoinhibition. Experiments on the effect of nutrient deficiency were inconclusive. It was demonstrated that populations could recover from severe photoinhibition within periods of less than 24 h and that when the water column is stable the population in the surface water adapts to become more resistant to photoinhibition.
PHOSPHATE ACCUMULATION IN FAGUS MYCORRHIZAS
Authors: HARLEY J. L. , MCCREADY C. C.
Published: May 2006

Summary

The quantities of polyphosphate formed in beech mycorrhizas during uptake of KH232PO4 were estimated after extraction with cold TCA and KOH. Over an absorption period of 19 h the proportion of absorbed phosphate converted into polyphosphate increases with external phosphate concentration from 22% in 0·16 mM to 44% in 0·98 mM KH2PO4. Uptake from 64 mM phosphate results in 39 % being accumulated as polyphosphate during 2·5 h. Calculations based on the percentage of phosphate accumulated in the sheath, obtained by dissection, show that a large fraction of the phosphate in the fungus is accumulated as polyphosphate.
ABUNDANCE OF MYCORRHIZAS AND ROOT‐SURFACE MICRO‐ORGANISMS OF PLANTAGO LANCEOLATA IN RELATION TO SOIL AND VEGETATION: A MULTI‐VARIATE APPROACH
Authors: NEWMAN E. I. , HEAP ALISON J. , LAWLEY R. A.
Published: May 2006

Summary

At 40 sites in England and South Wales, mostly in grassland, features of the soil and vegetation were measured. Three Plantago lanceolata individuals were collected from each site, nitrogen, phosphorus and potassium concentrations in the leaves were measured, and the abundance of mycorrhizal infection and of fungi and bacteria on the root surface was determined by microscopic examination of stained root segments. The results were subjected to multiple regression analysis.

Mycorrhizal abundance was most significantly related to vascular plant cover (negatively) and Plantago leaf length (positively), bacteria to soil organic matter (positively), fungi to cover of non‐grasses (positively) and leaf phosphorus concentration (negatively). The ecological interpretation of these relationships is discussed.
REGULATION OF PLANT CELL GROWTH: THE CHANGING PERSPECTIVE
Authors: HANSON J. B. , TREWAVAS A. J.
Published: May 2006

Summary

This article outlines the main features of growth regulation by auxin and places them side‐by‐side with the physiological properties of fusicoccin. The fundamental role of the plasma membrane located H+/K+ ATPase in growth responses is examined and the information about this enzyme briefly reviewed. The effects of wounding on the activity of this enzyme are detailed and it is concluded that growth in excised tissue segments ceases not from lack of hormone but from impairment of ATPase function. An additional conclusion of major importance for hormone studies is reached; that is, that the experimentally‐realized reactivation of growth by auxin in excised tissues represents largely an accelerated recovery from injury. Furthermore the calmodulin/Ca2+ system may be an essential intermediary in this recovery step. Finally, the major area of ignorance, predisposition to growth, is considered.
TOXICITY OF GLYPHOSATE APPLIED TO ROOTS OF BARLEY SEEDLINGS
Authors: PENN D. J. , LYNCH J. M.
Published: May 2006

Summary

The toxicity of glyphosate to barley seedlings when applied to the entire root system in water culture was such that at pH 7.5 the minimum lethal dose was around 15 mg l−1; 3 mg l−1 caused a 23 % decrease in shoot dry wt. Barley and wheat seedlings did not differ significantly in susceptibility. The growth of seminal roots with a short (5 mm) length of the tip exposed to 500 mg l−1 glyphosate in culture solution was decreased by about 50%. Unless a large amount of the root system of an establishing crop came into contact with the rhizomes of couch grass which had been treated with glyphosate, herbicide release by the rhizomes seems likely to be unimportant.
ROOT NODULES IN THE GENUS COLLETIA
Authors: BOND G. , BECKING J. H.
Published: May 2006

Summary

Following the earlier reported detection of root nodules on a species of Colletia growing in the Glasgow Botanic Gardens, the authors' enquiries have revealed that Colletia species are nodulated in some other botanic gardens, both in Europe and elsewhere. Cytological study of the nodules under the electron microscope shows that the endophyte is a procaryotic, actinomycete‐like organism consisting of septate, branching hyphae which are 0.37 to 0.53 μm in diameter and form terminal spherical vesicles 2.0 to 2.5 μm in diameter. The vesicles are internally sub‐divided and lie peripherally within the host cell. The endophyte is enclosed within a thin layer (or capsule) of material which judging by previous studies of other non‐legume nodules consists of carbohydrate‐related substances laid down by the host cytoplasm. Data from long‐term growth trials and acetylene assays show that Colletia nodules are nitrogen‐fixing and capable of satisfying the nitrogen‐needs of the host plant. Of the five genera of the Rhamnaceae that have so far been found to be nodule‐bearing, four (namely Colletia, Discaria, Trevoa and Talguenea) are in the tribe Colletieae, while the fifth genus (Ceanothus) is placed elsewhere in the family by taxonomists. A very similar situation exists in the Rosaceae as regards the distribution of nodulating genera and species. It is concluded that in these families the habit of symbiosis with a nitrogen‐fixing actinomycete probably arose, in some instances, prior to the establishment of now‐existing genera, but in others at a later stage. This conclusion is consistent with the belief that nodule symbioses were initiated in an earlier era when plants in general were subject to nitrogen stress.
METAL UPTAKE IN TERRICOLOUS LICHENS
Authors: GOYAL R. , SEAWARD M. R. D.
Published: May 2006

Summary

Laboratory experiments critically assess the role of rhizinae and thallial surfaces of Peltigera canina in the accumulation and translocation of metals (Cu, Fe, Mn, Ni, Pb and Zn) from the external medium to and within the thallus. The patterns of metal localization, within the different thallial components (rhizinae, medulla and phycobiont) observed from the analyses of field materials, are supported by laboratory experiments. The rhizinae were found to be capable of absorbing, accumulating, translocating and regulating metals. Both upper and lower surfaces were capable of metal translocation. The mode of translocation through one or both of the two surfaces was very similar. Metal cations were able to move freely from the rhizinae to the upper thallial surface and vice versa. The rhizinae and medulla play a significant role in metal accumulation and translocation, especially at higher metal concentrations when the metal uptake capacity of the upper thallial surface is reduced. The observed competitive metal uptake sequences by the rhizinae and thalli with rhizinae removed were consistent with an ion‐exchange process modified by a metal complex formation. The loss of K induced by metals was maximal from the rhizinae and medulla. Most of the metal binding sites are interpreted as occurring near, on, or within the fungal hyphae. Finally, modes of tolerance to high metal accumulations and detoxification are discussed in the light of the following observations: metal localization within the thallus, the role of rhizinae and thallial surfaces in metal uptake, and the lichen's morphological and histological performances in metal‐polluted environments. The factors limiting metal uptake and the effect of metal accumulations on the lichen's biological performance are given.
STUDIES ON THE CONTRIBUTION OF LIGNIN AND SUBERIN TO THE IMPEDANCE OF WOUNDED CARROT ROOT TISSUE TO FUNGAL INVASION
Authors: GARROD B. , LEWIS B. G. , BRITTAIN M. J. , DAVIES W. P.
Published: May 2006

Summary

During repair, phloem parenchyma cells near wound surfaces accumulated suberin and lignin. At 15 °C, all cells in the surface layer had become suberized within 48 h of wounding but lignification was slower, reaching a maximum at 168 h and the distribution was patchy. When fresh wounds were inoculated with Fusarium culmorum, Botrytis cinerea or Mycocentrospora acerina, patterns of lignification were not related in a simple way to pathogenicity; only Mycocentrospora acerina was stimulatory and remained localized in the wound surface bounded by heavily‐lignified cells.

If a 250 μm layer of tissue was removed from the surface of fresh or healed wounds its high impedance to Mycocentrospora acerina was substantially reduced by removal of antifungal substances. We therefore conclude that the development of structural barriers is less important than the accumulation of antifungal substances in the resistance of healing wounds.

A method for the quantitative estimation of lignin is described.
INTERACTION OF LIGHT AND MINERAL NUTRIENT SUPPLY IN THE GROWTH OF IMPATIENS PARVIFLORA
Authors: PEACE W. J. H. , GRUBB P. J.
Published: May 2006

Summary

(1) Plants of Impatiens parviflora were grown on a boulder‐clay woodland soil at four levels of irradiance with and without addition of ammonium nitrate and calcium phosphate.

(2) Addition of nitrogen and phosphorus fertilizer increased dry wt yield and relative growth rate at all four levels of irradiance, and there was a true interaction between the level of irradiance and nutrient supply.

(3) At the three higher levels of irradiance the increased growth resulted from an increase in unit leaf rate and leaf weight ratio, but at the lowest level an increase in leaf weight ratio alone was found.

(4) Evidence was obtained for lower rates of respiration in the leaves of plants grown with fertilizer at high irradiance. Mycorrhizas were absent from all fertilized plants, but were well developed in the unfertilized plants at high irradiance and absent from unfertilized plants at the lowest irradiance.

(5) Plants grown at high irradiance with additional phosphate alone responded initially exactly like plants with additional nitrogen and phosphorus but grew poorly later; plants with additional ammonium nitrate alone showed no response initially, but grew about as fast as plants with additional nitrogen and phosphorus later on.

(6) Plants grown one per small pot responded only to additional phosphate in the short term, but plants grown 10 per small pot responded only to additional nitrogen.

(7) Emphasis is placed on the important effects of the differential mobilities of nitrate and phosphate ions in experiments on the limiting mineral nutrients in soils.

(8) The results are discussed in relation to earlier work, and the penetration of deeper shade by herbs on soils of higher pH is tentatively related to a superior supply of nitrate.
DEGENERATION OF THE SALT GLANDS ACCOMPANYING FOLIAR MATURATION IN AVICENNIA MARINA (FORSSKÅL) VIERH
Authors: DRENNAN PHILIPPA M. , BERJAK PATRICIA
Published: May 2006

Summary

The salt excreting glands on both the adaxial and the abaxial surfaces of a sequential developmental series of leaves of Avicennia marina were studied at the light microscopic and ultrastructural level. Scanning electron and light microscopy have shown that there is a decrease in the total number of glands on the adaxial and abaxial surfaces as the leaf matures. From transmission electron microscopy it was established that the glands of emerging, unexpanded leaves exhibited most of the cytological features common to gland cells of all plant species. However, as the leaf expanded, the gland cells were observed to autolyse and the entire glandular structure to collapse. This loss of structural integrity of the glands coincided with abaxial stomatal development and the shift of salt excretion to this surface.
THE LATE‐GLACIAL AND EARLY FLANDRIAN DEPOSITS AT TRAETH MAWR, BRECON BEACONS, SOUTH WALES
Authors: WALKER M. J. C.
Published: May 2006

Summary

Pollen‐stratigraphic investigations are described from a site on the northern slopes of the Brecon Beacons, South Wales, in which over 5.0 m of Devensian Late‐glacial and early Flandrian sediments have accumulated. Relative (percentage) pollen concentration, and deteriorated pollen diagrams were constructed and these data were augmented by radiocarbon dates from the major stratigraphic boundaries. The evidence shows that relatively mild conditions characterized the Late‐glacial Interstadial, but these were succeeded at c. 10600 B.P. by the markedly colder phase of the Loch Lomond Stadial during which a severe periglacial climatic regime prevailed in the area. Climatic amelioration at c. 10000 B.P. led to a rapid sequence of vegetational changes and the establishment of a birch–hazel woodland on the lower slopes of the Brecon Beacons, possibly in the space of 1000 years. Of particular interest in the profile are fluctuations in both pollen percentages and pollen concentration values during the Late‐glacial Interstadial which are interpreted as reflecting major landscape changes around the site. Possible explanations for the fluctuations, which may well have been climatically‐induced, are discussed in the context of other Late‐glacial records from Wales, Highland Britain and northwest Europe.
EFFECT OF AMBIENT HUMIDITY AND LEAF DISPOSITION ON LEAF DIFFUSIVE CONDUCTANCE OF FESTUCA ARUNDINACEA CV. S170
Authors: SILCOCK R. G. , WILSON D.
Published: May 2006

Summary

The effects of changes in humidity on leaf diffusive conductance of Festuca arundinacea cv. SI 70 during a sequence of changes in leaf orientation were studied in a controlled environment cabinet. Reducing the vapour pressure deficit from 0.95 to 0.32 kPa at 25 °C (increasing relative humidity from 70 to 90 %) increased total leaf conductance by 73 %. Leaf orientation markedly influenced the conductance of individual leaf surfaces, the uppermost nearly always having the greater conductance.

Total leaf conductance was greater when the ridged adaxial surface was uppermost and, overall, the adaxial surface was more sensitive than the abaxial to humidity and orientation changes. Mean leaf conductance was significantly greater 8 h after the lights were switched on than after 1 and 4 h. Leaves which naturally displayed the adaxial surface upwards had a higher leaf conductance than those in which the abaxial surface was normally uppermost for most of their length.