bluuebunny/crossref_metadata_2025 huggingface dataset:
THE INFECTION PROCESS AND ULTRASTRUCTURE OF THE GUNNERA‐NOSTOC SYMBIOSIS
Authors: SILVESTER W. B. , McNAMARA P. J.
Published: May 2006

The two components of the Gunnera–Nostoc symbiosis were isolated, grown separately in culture and the association resynthesized in vitro. Both components develop normally when grown independently and Nostoc retains its ability to fix atmospheric nitrogen in symbiosis.

Infection by Nostoc is initiated when the alga grows on mucilage produced by an apical papillate gland. The alga develops rapidly, growing between the papillae and finally penetrating thin‐walled meristematic cells at the base of the gland. Resulting nodules contain intracellular algal cells within a host membrane envelope. The algae are considerably modified in thylakoid distribution and shape, and have a very high heterocyst frequency. At later stages, the algae are enclosed in a thickened wall continuous with that of the host cell.
CONCERNING THE SINUOUS SHAPE OF LEAF EPIDERMAL CELLS
Authors: KORN ROBERT W.
Published: May 2006

The geometric features of the sinuous shape of intercostal epidermal cells of the upper epidermis of the leaf of the fern Dryopteris thelypteris (L.) were studied. These cells have an average and probability distribution for the number of anticlinal walls similar to those in tissues expanding in two dimensions as reported earlier. No angles between anticlinal walls were <90° or >180° thereby indicating that growth stresses do not alter the shape of cells during the final expansion stage of development. Both the number of convex and concave lobes per cell approaches the binomial expansion of a2(p(a)+q(b))4 while the formula a4(p(a)+q(b))8 describes the distribution for all lobes. Rare gametophtyes were found in which the cells were transformed into sporophytic, leafy types including xylem, spines and sinuous epidermal cells. The occurrence of this last feature indicates that the wavyness of epidermal cells can be achieved in an isolated layer of cells.

The data best fit the hypothesis that each cell regardless of size and shape produces four growth centres, each of which arrives at a cell wall site by chance movements and forms either a concave or convex lobe.
TWO LATE‐GLACIAL (LATE DEVENSIAN) DIATOM ASSEMBLAGE PROFILES FROM NORTHERN SCOTLAND
Authors: HAWORTH ELIZABETH Y.
Published: May 2006

Two profiles of the diatom assemblages in lake sediments of Late Devensian age have been analysed in detail to substantiate a zonation based upon the diatom assemblages from the nearby Loch Sionascaig site, in northern Scotland. The profiles bear out the original divisions into three diatom assemblage zones and indicate some subdivisions; there is close correlation with stratigraphic, pollen and chemical changes. The Cam Loch assemblages did not include the planktonic phase found in the Sionascaig Diatom Zone 2 sediments of Allerød age, despite the proximity of the two sites and a geological location that would suggest a possibly richer environment.

It is concluded that the best pioneer forms are those of cosmopolitan distribution and that in the benthos at least there was an alkaline environment with sufficient nutrient status for diatoms typical of present day eutrophic lakes to occur during the period of greatest diatom diversity. The open water planktonic environment probably remained nutrient‐poor with little diatomaceous plankton, a condition resembling some present‐day alpine lakes.

The final cold phase of the late‐glacial is characterized by the temporary disappearance of many taxa and the presence of several indicator taxa. Solifluction of the surrounding land surface is indicated by the presence of some subaerial forms. This is also a feature of an earlier slight climatic recession indicated by correlation of pollen and diatom analyses and now correlated with the Bølling/Allerød stade.
POLAR TRANSPORT OF AUXIN THROUGH EMBRYOS
Authors: FRY S. C. , WANGERMANN ELISABETH
Published: May 2006

Hypocotyls of embryos from unripe and soaked ripe seeds of Phaseolus vulgaris and Acer pseudoplatanus are shown to be capable of transporting auxin. The transport is strongly polar and shows the characteristics of active transport in the basipetal but not the acropetal direction. A procambial cylinder and a few phloem elements have been formed in these hypocotyls.
A THEORETICAL ANALYSIS OF THE CONTRIBUTION OF ALGAL CELLS TO THE ATTENUATION OF LIGHT WITHIN NATURAL WATERS
Authors: KIRK J. T. O.
Published: May 2006

A theoretical treatment of light attenuation within phytoplankton suspensions, developed in a previous paper, has now been extended to certain non‐spherical cells and colonies of diatoms, blue‐green and green algae.

Procedures for calculating the mean absorption cross‐section for randomly oriented cells or colonies with the shape of cylinders, prolate spheroids or oblate spheroids, are described. The mean absorption cross‐sections at a series of wavelengths throughout the photosynthetic waveband are compared for model algae of various shapes, sizes and pigment compositions. The results clearly illustrate the principle that for a strongly absorbing algal cell/colony of a given volume, the more extended it is in space, the more effective it is as a light collector. The advantages of the more extended package are much less evident at wavelengths which are weakly absorbed.

For algae of a compact, e.g. spherical, shape a large cell or colony captures much less light (of a wavelength which is strongly absorbed) than an equivalent volume of smaller cells. However, it is also true that a large particle of very extended shape, e.g. a long thin cylinder, can capture as much light as a greater number of smaller particles (of the same total volume) of more compact shape. This means that for purposes of light collection an alga is almost as well off when organized into long multicellular filaments as it would be if separated into a large number of single cells.

Using the calculated values of mean absorption cross‐section the relationship between phytoplankton canopy structure and attenuation of photosynthetically active radiation (PAR) has been further investigated. Calculated values for the spectral distribution of light intensity, the total transmitted quantum flux, the vertical attenuation coefficients, and the increments in vertical attenuation coefficient per unit algal concentration, are presented for various model non‐scattering suspensions corresponding to common naturally‐occurring algae. The possible effects of turbidity on light attenuation in such systems are discussed.
EFFECT OF INFECTION BY MICROSPHAERA ALPHITOIDES (POWDERY MILDEW) ON CARBOHYDRATE LEVELS AND TRANSLOCATION IN SEEDLINGS OF QUERCUS ROBUR
Authors: HEWITT H. G. , AYRES P. G.
Published: May 2006

As infection of leaves of Quercus robur by Microsphaera alphitoides (powdery mildew) progressed, levels of total carbohydrate varied as first the rate of net photosynthesis declined and then an abnormal pattern of translocation was established. Infected leaves exported a smaller proportion of their photosynthate than did healthy leaves and imported a greater proportion of the photosynthate of healthy leaves on the same plant than did healthy leaves on healthy plants. Infection caused a decrease in the amounts of sucrose and insoluble glucose and an increase in amounts of glucose and fructose in leaf tissue. Evidence is presented that glucose and fructose were transferred to the fungus where they were converted to polyhydric alcohols and trehalose.
STUDIES ON DATA VARIABILITY AND THE USE OF POLYNOMIALS TO DESCRIBE PLANT GROWTH
Authors: ELIAS C. O. , CAUSTON D. R.
Published: May 2006

The question of which degree of polynomial should be fitted to plant data, for the purposes of growth analysis, has been considered in relation to the variability of the populations sampled. By means of actual and semi‐artificial data, it was shown that the variability of the samples taken at each harvest had a profound effect on the results of the tests of significance, when the relationship was fitted using individual observations. Significance tests performed on data of low variability resulted in over fitting, i.e. unrealistically high degrees were indicated as being most appropriate. Conversely, data of high variability were adequately fitted by lower order polynomials. In view of this, it is suggested that growth data should be fitted using harvest mean values, since in this case, the test of adequacy of fit is independent of the underlying population variability.
EFFECT OF ANAEROBIOSIS ON ACTIVITIES OF ALCOHOL DEHYDROGENASE AND PYRUVATE DECARBOXYLASE IN ROOTS OF ZEA MAYS
Authors: WIGNARAJAH K. , GREENWAY H.
Published: May 2006

Summary

Flushing of nitrogen gas through culture solutions, for periods between 4 and 15 h, increased activities of alcohol dehydrogenase (ADH) and pyruvate decarboxylase (PDC) in roots of intact maize plants (activities expressed as μmol mg protein−1 min−1). The activity of ADH was six to nine times greater than the activity of PDC.

Under root anaerobiosis of intact maize plants, activities of both ADH and PDC were similar in all root segments taken between o and 37 mm behind the apex, but lower activities were found in the older root segments. These differences in enzyme levels between younger and older root tissues were affected neither by the light regime of the shoots nor by imposing anaerobiosis of the shoots as well as the roots; i.e. the differences in ADH and PDC activities found in root segments of different ages were not due to a superior oxygen supply from the shoots to the tissues near the shoot‐root junction.

Roots of intact maize plants were also exposed to a range of oxygen concentrations, by flushing the nutrient solution with gases of different composition. ADH activities in the roots were highest with gas mixtures containing 8–13% oxygen, intermediate with pure nitrogen, and lowest when the solution was flushed with gas containing 20% oxygen.

It is concluded that ADH activity cannot be used to diagnose the degree of oxygen deficiency to which maize roots have been exposed.
EFFECT OF WATERLOGGING ON GROWTH AND ACTIVITY OF ALCOHOL DEHYDROGENASE IN BARLEY AND RICE
Authors: WIGNARAJAH K. , GREENWAY H. , JOHN C. D.
Published: May 2006

Summary

Flooding usually reduced shoot and root growth of barley. In addition, root growth was inhibited much more in flooding‐sensitive than flooding‐tolerant cultivars. Prolonged flooding resulted in larger increases in activity of alcohol dehydrogenase (ADH) in roots of flooding‐tolerant than flooding‐sensitive cultivars.

Barley and rice were also grown in solutions flushed with gases of different oxygen concentration. In rice roots, high activities of ADH and pyruvate decarboxylase (PDC) were found only when the solutions were flushed with pure N2 gas. In barley roots, activities of ADH and PDC were highest using gases between 3 and 13% O2, lower with pure N2, and very low when using 20% O2.

These results indicate that the level of ADH occurring in plant roots will be very dependent on experimental conditions, as for example root density. Species differences in activity of ADH might be mainly related to different oxygen tensions inside the roots, due in turn to differences in volume of aerenchyma and morphology of roots.
VESICULAR‐ARBUSCULAR MYCORRHIZA IN NATURAL VEGETATION SYSTEMS
Authors: KOUCHEKI H. K. , READ D. J.
Published: May 2006

Summary

The effects of vesicular‐arbuscular (VA) mycorrhizal association on the growth of Festuca ovina L. were assessed in soils sterilized by irradiation, in unsterilized soil, and in sand or sandpeat cultures with various nutrient additions.

In irradiated soils, effects of mycorrhizal infection were masked by nutrient release which proceeded through the first 4 months of growth. However, 9 months after inoculation, significant increases of yield and phosphorus content occurred in the mycorrhizal plants. When the irradiated soil was recovered and re‐used to grow a second crop, marked increases of yield and P content were observed in mycorrhizal plants. Growth in unsterilized field soil was very slow despite the fact that all the plants were heavily infected.

In sand culture, mycorrhizal plants were not significantly larger than non‐mycorrhizal controls when both were supplied with a full nutrient medium but differences between the two categories were evident when sand‐peat mixtures were supplemented with dilute nutrient medium and water.

The results are discussed in relation to the possible significance of mycorrhizal infection in the field.
EFFECT OF MYCORRHIZAL INFECTION ON RESPIRATION AND ACTIVITY OF SOME OXIDASE ENZYMES OF ORCHID PROTOCORMS
Authors: BLAKEMAN J. P. , MOKAHEL M. A. , HADLEY G.
Published: May 2006

Summary

Infection of protocorms of Dactylorhiza purpurella and a Cymbidium hybrid by an endophytic mycorrhizal fungus (Rhizoctonia sp.) led to a marked stimulation of respiration. Peak oxygen uptake often coincided with formation and digestion of pelotons. Treatment of protocorms with culture filtrates or mycelial extracts of the mycorrhizal fungus also enhanced oxygen uptake.

Activities of polyphenol oxidase, ascorbic acid oxidase, peroxidase and catalase were greatly increased in infected protocorms. Peak activity often coincided with peak oxygen uptake and digestion of pelotons, except for peroxidase where peak activity occurred earlier.

The orchid/endophyte system is compared with host/pathogen interactions in terms of the possible relationship between changes in enzyme activity and defence mechanisms.
THE INFLUENCE OF THE FREQUENCY OF WETTING AND DRYING ON THE RADIAL GROWTH OF THREE SAXICOLOUS LICHENS IN THE FIELD
Authors: ARMSTRONG R. A.
Published: May 2006

Summary

Three lichen species were wetted with distilled water at different frequencies during August 1973 to July 1974. The radial growth rates of Parmelia glabratula ssp. fuliginosa and Physcia orhicularis thalli declined with increased wetting while the radial growth rate of Parmelia conspersa thalli increased with wetting frequency until ten experimental wettings per month but at fifteen wettings per month fell to a value near to the control. In the summer months wetting resulted in a decline in the radial growth of P. glabratula ssp. fuliginosa compared with the control but had little influence on the growth of P. conspersa and Physcia orbicularis. In the winter months, wetting had no significant influence on the radial growth of Parmelia glabratula ssp. fuliginosa, while the radial growth of P. conspersa increased and Physcia orbicularis declined compared with controls. These results are interpreted physiologically and in relation to the aspect distribution of the three lichens on rock surfaces.
CELL PROLIFERATION IN, AND DEVELOPMENT OF, THE APICAL MERISTEM IN ELONGATING LATERAL ROOTS OF VICIA FABA L.
Authors: MACLEOD R. D.
Published: May 2006

Summary

Various aspects of cell proliferation have been examined in the stele and in the cortex‐epidermis between 50 and 800 μm basal to the junction between the cap initials and the rest of the meristem, in newly emerged, 0.2 and 4 cm long lateral roots of Viciafaba following a i‐h exposure to tritiated thymidine. Cell proliferation was found to differ in the two tissues in a number of ways, e.g. cell doubling time was usually shorter and the growth fraction generally larger in the cortexepidermis than in the stele. Cell proliferation changed basally along each tissue, especially in the relative and absolute sizes of the various meristematic and quiescent cell fractions and in cell doubling and mean cycling times. It was concluded that the apical meristem expanded longitudinally as the lateral roots lengthened from newly emerged to 4 cm. In terms of cell doubling time, although no change took place in the main site of cell proliferation in the cortex‐epidermis, that in the stele shifted basally along the root as the apical meristem expanded.
THE ROLE OF INVAGINATIONS IN ARMED MESOPHYLL CELLS OF PINE NEEDLES
Authors: WIEBE H. H. , AL‐SAADI H. A.
Published: May 2006

Summary

The distribution of air in the intercellular spaces of pine (Pinus ponderosa Laws) leaves was studied by sectioning the needles under water to trap the air and examining the sections microscopically. Air was present in the intercellular spaces of the chlorenchyma, including the invaginations of armed parenchyma cells. The air could be removed by vacuum or by sectioning the needles under paraffin oil which infiltrated the spaces. The invaginations are extensions of the leaf air space system and would increase conductivity of CO2 to the chloroplasts which line the invaginations.
COMPETITION FOR POLLINATORS AND EVOLUTION IN CENTAUREA
Authors: LACK ANDREW
Published: May 2006

Summary

Centaurea nigra s.l. forms a very variable complex which has received extensive taxonomic treatment. From analysis of previous work it is shown that populations growing on chalk and limestone in association with C. scabiosa flower later than those in the more typical habitat of neutral and acid grassland. The rayed form of the capitula is dominant in these populations, whereas elsewhere unrayed capitula predominate. From observations on the relative numbers of visiting insects, competition for pollinators with C. scabiosa is proposed as a major selective factor influencing these changes.
MORPHOGENESIS IN SCLEROTIUM‐FORMING FUNGI
Authors: HUMPHERSON‐JONES F. M. , COOKE R. C.
Published: May 2006

Sclerotium production by Sclerotinia sclerotiorum (Lib.) de Bary, Sclerotium rolfsii Sacc. and S. delphinii Welch was enhanced by white light, the most effective wavelengths being in the blue and near‐ultraviolet regions of the spectrum. Sensitivity of dark‐grown cultures to light decreased with age. The effect of light appeared to be through the direct induction of sclerotium initials on undifferentiated hyphae. The relevance of these observations to the general study of sclerotium morphogenesis is discussed.
MORPHOGENESIS IN SCLEROTIUM‐FORMING FUNGI
Authors: HUMPHERSON‐JONES F. M. , COOKE R. C.
Published: May 2006

Twenty‐six out of thirty‐six monoascospore isolates of Sclerotinia sclerotiorum (Lib.) de Bary, when grown in continuous darkness, produced regular zones of sclerotia. Patterns of zonation were independent of linear growth rate and, although rhythmic behaviour was endogenously determined, rhythms could be altered in detail by varying either glucose concentration or temperatue but not light regime. In some isolates, sclerotium production was accompanied by both generalized and localized changes in the growth rate of the colony margin. The implications of these observations are discussed in the context of nutrient availability and sclerotium morphogenesis.
DEMOGRAPHIC ANALYSIS OF THE GROWTH OF LINUM USITATISSIMUM
Authors: BAZZAZ F. A. , HARPER JOHN L.
Published: May 2006

Traditional growth analysis techniques have dealt with changes in plant weight and leaf area and have contributed a great deal to the understanding of plant growth. However, they have ignored the fact that the plant may be considered as a population of modules perfectly suited for studies of age structure. Plant growth has many analogies with the growth of a population of organisms. Plant modules (e.g. leaves) have a life cycle–birth, juvenile phase, ‘reproduction’ (i.e. contributing resources to the birth of other leaves and ultimately to flowering and seed set), senescence and death.

Plants of Linum usitatissimum were grown in a glasshouse under full and 50% light and at densities of 3.9 and 30/flat. Leaf birth rates were reduced by shading and especially by increased plant density. Light and density also influenced the branching pattern, the intrinsic rate of growth (rm), leaf survivorship, life expectancy (ex), and leaf death rates.

Leaf death was strongly influenced by the treatments. Regardless of leaf age, leaf area index, flowering time, density or light intensity, leaf death started when the total biomass of the plants was about 13 g/flat. This biomass apparently exceeded the carrying capacity of the soil medium. Experimentally withholding nutrients, shading the lower parts of the plants, and the removal of flower buds influenced the onset of leaf death but the variable that was most effective, was the withholding of nutrients. Death started in the lower leaves and proceeded upwards regardless of leaf age. The number of seeds per plant was more strongly correlated with the number of leaves than with the total leaf area per plant. This study shows that the application of life‐table and other demographic analyses to leaf birth and death is feasible and permits an interpretation of plant response to environmental factors at a more sophisticated level than is possible from classical growth analysis.
THE EFFECTS OF THE AXIS AND PLANT HORMONES ON THE MOBILIZATION OF STORAGE MATERIALS IN THE GROUND‐NUT (ARACHIS HYPOGAEA) DURING GERMINATION
Authors: ALLFREY J. M. , NORTHCOTE D. H.
Published: May 2006

During germination the lipids, triglycerides and starch stored in the cotyledons of the ground nut are mobilized. The time course of this degradation has been measured and the accumulation of mono‐ and diglycerides, free fatty acids, phospholipids, cholesterol and sucrose has been estimated during the first 8 days of development. During this time the lipase and amylase activities present in the seeds increased. The lipase appeared to be relatively unspecific. A feature of germination was the induction of isocitrate lyase activity which was not present in the seed before germination. The action of gibberellic acid, abscisic acid and ethylene on germination, mobilization of reserves and enzyme induction had been studied.

Application of abscisic acid inhibited germination and also the increase in lipase activity. It also inhibited strongly the induction of isocitrate lyase, but it increased amylase activity and starch breakdown. The presence of the axis in the germinating seeds helps to restore normal metabolism when it is disturbed by the application of the exogenous growth substances.

The results are discussed in relation to the balance between fat and carbohydrate metabolism of the germinating seed and the importance of isocitrate lyase as a control point connecting the two aspects of this metabolism.
STEM ELONGATION IN TULIP AND NARCISSUS: THE INFLUENCE OF FLORAL ORGANS AND GROWTH REGULATORS
Authors: HANKS GORDON R. , REES A. R.
Published: May 2006

Decapitation of tulips early in extension growth resulted in a 59% reduction in stem length at flowering. Selective removal of the floral parts showed that the gynoecium controlled stem extension. The upper internodes were most affected, and the effect was largely reversed by the application of indol‐3‐ylacetic acid (IAA) but not by gibberellic acid (GA). Soil drenches of ancymidol also reduced tulip stem extension, but in this case the lower internodes were most affected and this effect was reversed by GA.

The result of flower removal in narcissus was similar to that in tulip, although the narcissus scope and the tulip stem differ morphologically. Scape extension of narcissus was reduced by decapitation; this was due entirely to the removal of the gynoecium and could be reversed by IAA but not GA. In narcissus, spathe removal led to earlier flowering.

Flower blasting in tulip (a drying out of the flower which occurs commercially under some conditions) resulted from a number of treatments, including floral surgery, injections and ancymidol soil drenches. The incidence of flower blasting was reduced by injecting GA or kinetin.

The results are discussed in relation to commerical flower production, the control of pot‐plant height, and the prevention of flower blasting.
CHLOROPLAST DEVELOPMENT IN YOUNG SESAME PLANTS
Authors: PLATT‐ALOIA K. A. , THOMSON W. W.
Published: May 2006

Electron microscopic examination of developing chloroplasts of sesame indicates that plastids in the shoot apex and leaf buds contain a membrane‐bound inclusion with electron‐dense, homogenous contents. The incipient grana of these young plastids have enlarged loculi filled with an electron‐dense material, and the membranes exhibit a ‘negative’ image. The bounding membrane of the inclusion is frequently observed in intimate contact with, and possibly contiguous with, the grana‐fretwork system of the developing chloroplast. As development continues, many of the inclusions are observed to contain partly or wholly crystalline contents, the locular content of electron‐dense material decreases, and the ‘negative’ membrane image disappears. With further maturation, the inclusions become smaller, and eventually disappear.

It is suggested that, in accordance with other studies, the membrane‐bound inclusion of developing sesame leaf chloroplasts is a storage centre for thylakoid precursor materials. The ‘negative’ image observed in the incipient grana may also be a reflection of incomplete assembly of the membranes associated with the accumulation of material within the loculus.
EXPERIMENTS ON THE FACTORS INFLUENCING THE GEOGRAPHICAL DISTRIBUTIONS OF SACCORHIZA POLYSCHIDES AND SACCORHIZA DERMATODEA
Authors: NORTON TREVOR A.
Published: May 2006

To investigate the possible causes of the contrasting geographical distributions of Saccorhiza polyschides (Lightf.) Batt. and S. dermatodea (Pyl.) J. Ag., sporophytes of both species were cultured from zoospores under a variety of conditions. The spores of both species were able to survive in the dark for at least 6 months. Thus although, unlike S. dermatodea, S. polyschides is not found within the Arctic Circle, it too can survive the equivalent of the Arctic winter night without light.

Water temperatures from 3° C to 25° C were found to influence every stage in the development of both plants from spore settlement and germination, to the production and rate of growth of the sporophytes and it was particularly critical to the fertility of the female gametophyte and to the survival of the sporophyte. The female gametophytes of S. dermatodea became fertile only between 3°C and 10°C, producing numerous sporophytes at 3°C and 5°C but rather few at 10°C. In contrast, those of S. polyschides produced an abundance of sporophytes from 5°C to 17°C, relatively few at 20 and 23°C and none at either 3°C or 25°C. Some grossly abnormal sporophytes were produced at the temperatures close to the tolerance limits of the species. Gametophytes cultured at temperatures unfavourable for sporophyte production survived, but rapidly lost their ability to produce sporophytes.

The close correlation between these tolerances and the sea temperatures prevalent at the geographical limits of each species strongly suggests that the absence of S. polyschides from within the Arctic Circle is related to its inability to reproduce sexually or to survive at low water temperatures and that the southward extension of both S. dermatodea and S. polyschides and the unusual distribution of the latter species in the Mediterranean are probably the result of their failure to tolerate the higher sea temperatures during the growing period in summer.
HYPERSENSITIVE REACTIONS OF TOMATO LEAVES TO PHYTOPHTHORA INFESTANS
Authors: MATTHEWSON D. K.
Published: May 2006

Tomato and potato leaves were inoculated with either a compatible or an incompatible strain of Phytophthora infestans. The progress of the ensuing progressive or hypersensitive reactions were followed using light microscopy. Transverse sections of tissue as well as strips of living epidermis were examined. Cell death was found to occur within 10 min of infection by an incompatible strain of the fungus. The migration of the host nucleus to the site of infection, in the hypersensitive reaction, was observed.
SOME FACTORS LIMITING NITRATE UTILIZATION IN ACIDIC AND CALCAREOUS GRASSLANDS
Authors: HAVILL D. C. , LEE J. A. , DE‐FELICE J.
Published: May 2006

Factors limiting nitrate utilization by plants in acidic and calcareous grassland were examined by analysis of control and ammonium‐fertilized plant and soil material from the field. Plants from these habitats maintained their maximum capacity to synthesize nitrate reductase throughout the growing season. In both soil types, nitrate formation was limited by the ammonium supply. Increasing the availability of soil ammonium stimulated the rate of nitrate utilization. However, in plants from calcareous soils, water stress often impaired nitrate reductase activity. Consequently, during periods of drought, nitrate utilization may be higher in acidic soils than in closely adjacent calcareous sites.
SELF‐POLLEN REDUCES THE NUMBER OF CROSS‐POLLEN TUBES IN THE STYLES OF BRASSICA OLERACEA L.
Authors: OCKENDON D. J. , CURRAH LESLEY
Published: May 2006

The number of cross‐pollen tubes in the styles of self‐incompatible kale plants was reduced by 46–94% when self‐pollen was applied to the stigma immediately before the cross‐pollen. Similar reductions were found when the cross‐pollen was applied at time intervals of 2–16 h after the self‐pollen, but little or no reduction occurred when the time interval was 24 h or 32 h. No reductions were found when cross‐pollen was applied before self‐pollen nor when dead cross‐pollen was applied before the live cross‐pollen. Application of onion pollen before cross‐pollen gave a mean reduction of 69%. The results are discussed in the context of current views on the mechanism of self‐incompatibility in Brassica, and their practical implications for the breeding of F1 hybrid brassicas.
MODERN POLLEN RAIN IN FINNISH LAPLAND INVESTIGATED BY ANALYSIS OF SURFACE MOSS SAMPLES
Authors: HICKS SHEILA
Published: May 2006

The results of pollen analyses from ten surface moss samples collected from the different regional vegetation types of northern Finland are presented. The main features distinguishing the pollen assemblages and the trends observable in transecting the series of vegetation types are outlined and compared with the results of similar studies from elsewhere. With the aim of using the modern pollen assemblages to interpret fossil ones, a simple graphical method of classifying the boreal assemblages is given and specific limits for the forest types presented are suggested. The inability of this graph to distinguish ‘tundra’ assemblages is noted and additional criteria for separating out this regional type are detailed. Emphasis is also placed on the importance of having absolute pollen frequency values to supplement the relative ones.
A LATE‐GLACIAL AND EARLY POST‐GLACIAL POLLEN DIAGRAM FROM DRIMNAGALL, NORTH KNAPDALE, ARGYLLSHIRE
Authors: RYMER LESLIE
Published: May 2006

The Late Devensian and early Flandrian pollen and sediment stratigraphy of a site from a valley fen at Drimnagall, North Knapdale, Mid Argyll, are described. Six pollen assemblage zones are recognized, of which five arethought to be Late Devensian, and one to be Fiandrian. The assemblage zones, which are more similar to those recognised from Caernarvonshire than to those recognised from the north‐west of Scotland, are interpreted in terms of the vegetational and environmental history of the site.
CHANGES IN CHLOROPHYLL AND CAROTENOID CONTENT, SPECIFIC LEAF AREA AND DRY WEIGHT FRACTION IN SITKA SPRUCE, IN RESPONSE TO SHADING AND SEASON
Authors: LEWANDOWSKA M. , JARVIS P. G.
Published: May 2006

The response of chlorophyll and carotenoid concentration, specific leaf area and dry weight fraction in shoots of Sitka spruce (Picea sitchensis (Bong.) Carr.) to season and photon flux density has been measured. Shoots were sampled from different heights in the canopy at two forest sites, one thinned, the other unthinned. An increase in specific leaf area and a decrease in dry weight fraction was found in shaded shoots. At both sites, there was a seasonal variation in pigment content, with a summer maximum for chlorophyll and a winter maximum for carotenoid. Pigment content was constant throughout the canopy on the thinned site, but was higher in shaded shoots from the unthinned site.
CADMIUM TOLERANCE OF HOLCUS LANATUS FROM A SITE CONTAMINATED BY AERIAL FALLOUT
Authors: COUGHTREY P. J. , MARTIN M. H.
Published: May 2006

Holcus lanatus, collected 2.8 km from a large smelting complex, exhibited distinct tolerance to cadmium. Tolerant plants grew less well on normal culture solution than non‐tolerant plants but grew roots at normal rates in the presence of concentrations of cadmium related to those present in the field. These results are discussed in relation to the previous literature of metal tolerance and reference is made to the problems associated with the quantitative measurement of tolerance.
A NOTE ON THE GERMINATION OF NARCISSUS BULBOCODIUM L.
Authors: THOMPSON P. A.
Published: May 2006

Seeds of Narcissus bulbocodium were exposed to a series of successive temperature treatments involving transfers between incubators and thermogradient bars. Freshly harvested seeds were dormant and failed to germinate at any temperature over the range 3–38°C. A conditioning treatment at 26°C applied to imbibed seeds induced changes which resulted in rapid germination of very high proportions of seed after transfer to temperatures between 5 and 16°C. A conditioning treatment at 16°C was less effective, and at 6°C was practically ineffective. It is suggested that the seed is protected from premature germination under natural conditions by high summer temperatures which themselves act as conditioning treatments and induce the changes which result in rapid spontaneous germination as temperatures fall in autumn at the start of the winter rains.
RESPONSE OF A WILD‐TYPE AND A NON‐NITROGEN‐FIXING MUTANT OF NOSTOC LINCKIA TO DIFFERENT CARBON SOURCES
Authors: LADHA J. K. , KUMAR H. D.
Published: May 2006

The wild‐type parental strain and a het+nif− mutant of Nostoc linckia grow heterotrophically in light, with and without DCMU, and in darkness when supplemented with a source of carbon. Glucose and sucrose stimulated heterocyst production. Glucose enhanced the uptake of ammoniacal nitrogen from the medium when parent and mutant were grown in an ammonium‐supplemented medium. Effects of cAMP (sodium salt and dibutyryl), with and without glucose, on growth and heterocyst differentiation of parent and mutant were studied. Dibutyryl cAMP, in general, was found to be toxic to the alga, but the sodium salt of cAMP enhanced growth with glucose. The mutant grew well in a nitrogen‐free medium supplemented with cAMP.
ROOT ORGANOGENESIS FROM FOLIAR DISCS OF CREPIS CAPILLARIS L. WALLR. CULTURED IN VITRO: CYTOCHEMICAL AND MICROSPECTROPHOTOMETRIC ANALYSIS
Authors: BROSSARD DOMINIQUE
Published: May 2006

Neoformed roots always arose at the upper surface of Crepis capillaris foliar discs grown in vitro on Murashige and Skoog's medium supplemented with indolylacetic acid (10−5 M). Root meristems originated endogenously but direct dedifferentiation of parenchymatous cells located in the vicinity of the leaf veins, in a perivascular position and without any previous callus formation. Their initiation was accompanied by an increase in the starch content of the explants and a strongly starch‐positive zone was always detected in the parenchyma underlying their site of initiation. Cytophotometric examination of the nuclear DNA contents of foliar tissues confirmed their non‐polyploid constitution. The exclusively diploid condition of all the neoformed root meristems was also established.
A MORPHOLOGICAL AND CYTOLOGICAL INVESTIGATION OF COCHLEARIA POPULATIONS ON THE GOWER PENINSULA, GLAMORGAN
Authors: FEARN G. M.
Published: May 2006

Populations of Cochlearia officinalis L. and C. danica L. have been investigated on the Gower Peninsula (v.c. 41) and introgressive hybridisation between the two species is suspected of occurring on Worms Head. Individuals in the hybrid population are apparently highly fertile and preferential backcrossing to C. officinalis is thought to be responsible for the enrichment of that species with morphological characters from C. danica. Evidence is presented in support of the theory that plants carrying the ‘B’ chromosomes which are found in certain populations of C. officinalis are segregants from such hybrids.
TOLERANCE TO SALT, PARTIAL ANAEROBIOSIS, AND OSMOTIC STRESS IN AGROSTIS STOLONIFERA
Authors: AHMAD I. , WAINWRIGHT S. J.
Published: May 2006

The tolerance to sodium chloride of clones of Agrostis stolonifera from salt marsh, spray zone, and inland habitats was measured in water cultures by a rooting technique and by growth analysis. The order of tolerance was found to be: salt marsh > spray zone > inland. The two methods of measurement of tolerance were found to show good agreement. Salt marsh plants were found to be more resistant to low dissolved oxygen concentrations in the culture solution than plants from the spray zone and inland habitats. With polyethylene glycol 6000 in culture solution, the pattern of resistance to osmotic stress in the absence of sodium chloride was similar to the pattern of resistance to salt.
PLANT COMMUNITIES OF THE ISLAND OF ARRAN, SCOTLAND
Authors: ADAM P. , BIRKS H. J. B. , HUNTLEY B.
Published: May 2006

The vegetation of the saltmarshes, raised‐beaches, inland mires, dwarf‐shrub heaths, mountains, and woodlands of the Isle of Arran are described using conventional European phytosociological methods. The floristic affinities of these communities with previously delimited units elsewhere in Britain and in western Europe are described, and the problems of assigning many of the Arran communities into the existing central European phytosociological hierarchy are discussed.
THE BIOLOGY OF MYCORRHIZA IN HELIANTHEMUM MILL
Authors: READ D. J. , KIANMEHR H. , MALIBARI A.
Published: May 2006

The mycorrhizal status of Helianthemum chamaecistus was assessed. Vegetative and reproductive tissues of mature plants were free from infection by a fungus capable of producing mycorrhizas and were normally free from any internal fungal infection. The mature gelatinous sheath of the seed was infected by a number of non‐mycorrhizal fungi of which the commonest were the saprophytes, Cladosporium herbarum and Ulocladium chartarum. The so called ‘tuberous roots’ are typical ecto‐mycorrhizal short roots. They develop following infection by a soil‐borne sclerotium‐producing fungus. Isolates of the sclerotia and roots produced typical mycorrhizal short roots in sterile cultures of both Helianthemum and Betula pubescens. This mycorrhizal associate is believed to be Cenococcum graniforme. It is concluded that cyclic infection does not occur in Helianthemum and that the mycorrhizal status of members of this genus is comparable with that of many woody species. The possible ecological significance of the mycorrhizal association is discussed.
SEED ACTIVATION AND SEED GERMINATION UNDER MOISTURE STRESS
Authors: HEGARTY T.W.
Published: May 2006

Seeds of calabrese and carrot were held at 10°C or 20°C for periods of up to 21 days in water or polyethylene glycol ‘6000’ solutions of from −5 to −20 bars. Seeds were subsequently placed to germinate in a favourable environment or were first dehydrated before transfer to this environment. The seeds’ ability to germinate was virtually unaffected by any of the temperature, water potential or duration treatments. Increasing water stress progressively reduced the levels of water content and oxygen uptake rates after initial imbibition, and delayed the onset of germination with the accompanying increase in these factors. At −15 and −20 bars, water content remained approximately constant throughout the experiment but oxygen uptake rates fell after day 6. The results have a direct bearing both on the seed ‘priming’ treatment used to accelerate seed germination and on the tolerance to drought of seeds in the field.
ACETYLENE REDUCTION BY BLUE‐GREEN ALGAE IN SUB‐TROPICAL GRASSLAND
Authors: JONES KEITH
Published: May 2006

In situ measurements using the acetylene reduction technique showed that mats of blue‐green algae found amongst kikuyu grass fixed nitrogen throughout the day and night. Daylight fixation increased throughout the morning, fell during the hottest part of the day, and reached a peak (19.2 mg C2H4 m−2 h−1) during the afternoon. Nitrogen fixation was higher on overcast days than on hot sunny days. Nocturnal fixation was also due to blue‐green algae and was sensitive to temperature changes.
THE CYANOPHYTE‐HEPATIC SYMBIOSIS I. MORPHOLOGY AND PHYSIOLOGY
Authors: RODGERS G. A. , STEWART W. D. P.
Published: May 2006

The Anthoceros punctatus‐Nostoc and Blasia pusilla‐Nostoc symbioses were investigated. In both associations the Nostoc colonies develop in mucilaginous cavities on the undersurface of the gametophyte. The sporophytes of Anthoceros have no Nostoc colonies; no sporophytes of Blasia were found. The symbiotic algae have been identified as Nostoc sphaericum ex. Born et Flah. The heterocyst frequency of the free‐living isolates is 3–6% but this increases to 30% (Blasia) and 43% (Anthoceros) when the algae are growing symbiotically. On infecting alga‐free gametophytes of Blasia pusilla with Nostoc, algal colonies develop in the cavities within 72 h. The developing Nostoc colonies stretch the cells of the cavity wall and there also arise from a point on the host cavity wall, usually opposite the cavity pore, septate, branched, filamentous protrusions, which increase the surface area of contact between phycobiont and host by about 30% within 4 weeks of colony formation. Such outgrowths may facilitate interchange of metabolites between the alga and liverwort. The Nostoc phycobiont of Anthoceros may infect Blasia and vice‐versa. A strain of Nostoc punctiforme isolated from Gunnera also infects Blasia, but four other Nostoc isolates, including one from cycad root nodules, do not. Five other heterocystous algae, five non‐heterocystous filamentous algae and one unicellular alga tested do not infect Blasia. The nitrogen contents of thalli with Nostoc colonies are significantly higher than those treated with algae which do not develop colonies. The symbiotic algae differ physiologically and biochemically from free‐living algae. They show higher rates of nitrogenase activity (acetylene reduction assay), are depleted of nitrogen‐storing phycobilin pigments and structured granules and although metabolically active do not evolve O2 or fix CO2 photosynthetically, but do have polyhedral bodies which contain the key CO2‐fixing enzyme ribulose‐l,5‐diphosphate carboxylase. The Blasia symbiosis grows well and remains established in the pH range 4–8, at low levels of combined nitrogen (<100 mg I−1 of nitrate‐nitrogen) but not at high levels (100–1000 mg I−1), in the temperature range 10–25°C, and under moist but not waterlogged or desiccated conditions.
DIURNAL PERIODICITY IN SOME COMMON FLOWERS
Authors: EWUSIE J. YANNEY , QUAYE E. C.
Published: May 2006

The time of flower opening and closure has been observed in twenty species belonging to nine different families. Increasing light initiates opening in some flowers and different species have different thresholds of response. Other species appear to be unaffected by light intensity.

Experiments on the effect of photoperiod on petal movement in Talinum triangulare and Mirabilis jalapa indicate that the photo‐fraction affects the period of the rhythm by altering phase‐timing. A close correlation is suggested between phase‐timing and the automatic self‐pollination mechanism in Talinum possibly also in Mirabilis.

Temperature also modifies the period of the rhythm in Tradescantia and Talinum; in the latter, a temperature of 24°C promoted closing.
A HOXNIAN INTERGLACIAL SITE AT FISHERS GREEN, STEVENAGE, HERTFORDSHIRE
Authors: GIBBARD P. L. , AALTO M. M. , BEALES P. W.
Published: May 2006

Interglacial deposits resting on glacial till and overlain by fluviatile sand and gravel 2 km (1.5 miles) north‐north‐west of Stevenage are shown to be of Hoxnian age. The lower part of the deposit consists of calcareous silty clay formed under late‐glacial and early interglacial conditions with Hippophaë shrubs and Betula woodland in a shallow water pool which contained an abundant flora and fauna. The upper part of the deposit consists of organic sediment and represents the second half of the interglacial during which coniferous trees were dominant. The fragmentary sequence, which is also found at other Hoxnian sites in Hertfordshire, is shown to result from water level changes. The recognition of these changes elsewhere in Eastern England indicates that they may be climatically controlled and thus reflect periods of alternating moister and drier conditons.
NITROGEN METABOLISM OF HALOPHYTES III. ENZYMES OF AMMONIA ASSIMILATION
Authors: STEWART G. R. , RHODES DAVID
Published: May 2006

The occurrence of glutamine synthetase, glutamate synthase and glutamate dehydrogenase in a range of halophytic higher plants has been investigated. Ferredoxin‐dependent glutamate synthase was found in shoot tissue of all the species examined. Root tissue glutamate synthase was active with both reduced pyridine nucleotides and reduced ferredoxin. The levels of enzymes present in the majority of species are consistent with the view that ammonia assimilation occurs via the combined action of glutamine synthetase and glutamate synthase. An increase in external salinity lowers the levels of glutamine synthetase and glutamate dehydrogenase of root tissue but increases the level of shoot glutamine synthetase.
THE TOLERANCE OF TREE ROOTS TO WATERLOGGING
Authors: PHILIPSON J. J. , COUTTS M. P.
Published: May 2006

Seedling root systems, or individual roots of cuttings, were submerged in reduced indigo‐carmine solution so that only the seedling shoot, or basal part of the cutting root, was exposed to air or oxygen. Oxygen diffusing out of the roots produced a localized blue colouration of the previously clear reduced dye; this process was employed to study internal oxygen movement.

Using plants grown in freely drained soil it was evident that seedlings of the flood‐tolerant species, Lodgepole pine, had a greater capacity for oxygen transport than the flood‐intolerant Sitka spruce. Oxygen diffusion was also observed in roots detached from Lodgepole pine cuttings and was greatly enhanced in plants which had grown in waterlogged conditions; in the latter plants oxygen diffusion was detected from the root tips after a short exposure of the basal region of the root to oxygen, whereas roots from plants grown in freely drained soil showed diffusion of oxygen only from the upper submerged portion during the same treatment period. Oxygen diffusion over distances of more than 30 cm was detected in certain experiments.

Observations on the movement of gas supplied under pressure to Lodgepole pine root segments showed that the rate of gas flow was much greater in roots grown in waterlogged soil than in those grown in freely drained soil and that the gas movement occurred in the stelar tissues. The regions of oxygen entry included the needles, and lenticels on the roots.
LIMITATION OF GAEUMANNOMYCES GRAMINIS BY WHEAT ROOT RESPONSES TO PHIALOPHORA RADICICOLA
Authors: SPEAKMAN J. B. , LEWIS B. G.
Published: May 2006

Changes in wheat roots invaded by Phialophora radicicola var. graminicola, P. radicicola var. radicicola and Gaeumannomyces graminis var. tritici were explored. Progress of Phialophora radicicola var. graminicola was arrested by lignitubers in the third cortical layer whereas P. radicicola var. radicicola progressed as far as the innermost layer of the cortex, failing to penetrate the endodermis, but was not arrested by detectable structural changes. Both varieties of P. radicicola elicited considerable lignification of the stelar components, and lignification and suberization of the inner tangential wall of the endodermis. When the two species of fungi were inoculated on the same root, P. radicicola var. graminicola prevented Gaeumannomyces graminis var. tritici from spreading longitudinally in the stele.
STUDIES ON OUTER EPIDERMAL CELL WALLS WITH MICROCHANNELS IN A XEROPHYTIC SPECIES
Authors: LYSHEDE OLE B.
Published: May 2006

In the thick cutinized outer epidermal wall in the stem of Spartocytisus filipes radiating microchannels have been observed. The structure of the wall and the microchannels have been investigated by histochemistry, polarized light, and electron microscopy. The micro‐channels contain pectic substances and branch richly. The structure of the wall and the microchannels are discussed in relation to the ecology of the plant.