bluuebunny/crossref_metadata_2025 huggingface dataset:
THE ONTOGENY OF THE VASCULAR CAMBIUM IN HOHERIA ANGUSTIFOLIA RAOUL.
Authors: BUTTERFIELD B. G.
Published: May 2006

The procambium in Hoheria angustifolia (Malvaceae) develops behind the apical meristem as an almost complete cylinder of meristematic cells. Differentiating protophloem strands are separated by narrow interfascicular sectors. These sectors also interrupt the procambial cylinder. The first protoxylem elements differentiate as discrete bundles to the inside of a number of protophloem strands and remain separated from them by an actively dividing procambial cylinder six to eight cells wide. Periclinal divisions also occur in the interfascicular sectors so that by the centre of the first internode below the shoot tip the procambium forms a complete cylinder. In this way the short cells of the interfascicular sectors become transformed into primordial ray intitials. Repeated periclinal division in the procambium leads to the radial seriation of its cells. Subsequent differentiation of the derivatives produces complete cylinders of metaxylem and metaphloem by the third internode.

Internodal elongation ends by the fifth or sixth internode below the shoot tip after which the transverse ended primordial fusiform cells of the procambium become transformed into fusiform cambial cells with pointed tips. Except during ray formation, transverse division ceases and the non‐storeyed cambium gradually acquires a storeyed appearance in tangential view by repeated radial longitudinal divisions accompanying radial growth. The first new rays appear about the seventh internode.

The transition from procambium to cambium in Hoheria angustifolia is a gradual one with the meristem acquiring some cambial characteristics before and some after internodal elongation has ceased.
TRANSLOCATION OF LABELLED ASSIMILATE IN POTASSIUM‐DEFICIENT PLANTS
Authors: THROWER STELLA L. , THROWER L. B.
Published: May 2006

Summary

The pattern of distribution of labelled assimilate, and the amounts exported from a source leaf, have been investigated in eleven species of plants growing in a potassium‐deficient medium. Comparison with the same parameters for plants growing with full nutrient complement showed no detectable differences in either the pattern or quantity of photosynthate that was translocated.
EFFECT OF POTASSIUM ON PROLINE ACCUMULATION IN CUCUMBER COTYLEDONS
Authors: UDAYAKUMAR M. , RAO S. RAMA , PRASAD T. G. , SASTRY K. S. KRISHNA
Published: May 2006

Summary

Free proline accumulation in excised cucumber cotyledons and in leaves of cowpea seedlings increased after treatment of the plants with potassium chloride. In excised cucumber cotyledons there was less K‐induced proline accumulation in the presence of benzyladenine (BA) and free proline disappeared when cotyledons were transferred to BA. Cycloheximide increased the proline content in the tissue when present alone or in combination with BA and/or K. Under simulated water stress, the proline content increased but the increase was greater in cotyledons also treated with KCl. In cowpea seedlings, reduction in relative water content (RWC) under stress was much less in seedlings treated with additional amounts of KCl, and their praline content was also high. There appears to be thus a relationship between K content, praline accumulation and water content of the leaves.
HIGH TEMPERATURE REQUIREMENT FOR AFTERRIPENING IN SEEDS OF WINTER ANNUALS
Authors: BASKIN JERRY M. , BASKIN CAROL C.
Published: May 2006

Summary

Temperature requirements for afterripening were investigated in seeds of the winter annuals, Stellaria media, Valerianella umbilicata and Phacelia purshii. Seeds were incubated during the summer dormancy period at nine temperature regimes on wet and alternately wetted and dried sand. Low temperatures (5, 10, 15, 15/6 and 20/10°C) inhibited and high temperatures (20, 25, 30/15 and 35/20°C) promoted afterripening of the seeds. Temperatures (5 and 10°C) which promote afterripening in species with a chilling requirement (e.g., summer annuals) almost completely prevented afterripening of the three winter annuals. Thus, although dormancy is an adaptation of winter annuals to their hot, dry summer habitat, the summer temperatures are required for afterripening of the seeds.
THE PHYSIOLOGY OF NEOSPONGIOCOCCUM OVATUM DEASON
Authors: KHADKE VIMAL , MERRETT MICHAEL J.
Published: May 2006

Summary

By enrichment culture and conventional microbiological techniques the dominant alga of sewage trickle filters was obtained in axenic culture and identified as Neospongiococcutn ovatum Deason. A wide range of carbon compounds failed to support heterotrophic growth or alter the mean generation time or final cell yield in the light. The rate of photosynthetic carbon dioxide fixation was also unaffected by the growth conditions. The enzymes of the tricarboxylic acid cycle were present at comparable specific activity in cell extracts, but significant uptake of [14C]‐acetate or [14C]‐glycollate was not detected. It is suggested that impermeability to exogenous compounds may be an advantage in a toxic environment.
THE HORMONAL CONTROL OF CELL WALL TURNOVER IN PISUM SATIVUM L.
Authors: GILKES N. R. , HALL M. A.
Published: May 2006

A tentative structure for the polysaccharides of pea epicotyl cell walls is presented. The turnover of these polysaccharides has been followed by gravimetric and pulse chase studies. It is suggested that an important effect of IAA is the promotion of turnover in certain wall hemi‐celluloses, notably xyloglucan; moreover, such turnover appears to be inhibited by kinetin. The relevance of these findings is discussed in terms of longitudinal and lateral cell expansion.
ULTRASTRUCTURAL STUDIES IN THE BROWN ALGA ECTOCARPUS IN CULTURE: AUTOLYSIS*
Authors: OLIVEIRA LUIS , BISALPUTRA THANA
Published: May 2006

During autolysis of senescent cells of the brown alga Ectocarpus the disintegration of nuclei, endoplasmic reticulum, and Golgi apparatus is completed. Degenerating mitochondria and plastids remain as the only recognizable organelles. Results from ultrastructural study in correlation with cytochemical localization of acid phosphatase indicate that lysosomal compartmentation no longer exists because the acid phosphatase reaction becomes distributed throughout the remainder of the cytoplasm and is also shown by the disintegrating plasmodesmata. Aspects of cell wall breakdown are described and related to knowledge of the chemistry of the cell wall.
CONTROL OF RESPIRATION OF BEECH MYCORRHIZAS DURING AGEING
Authors: HARLEY J. L. , McCREADY C. C. , WEDDING R. T.
Published: May 2006

A detailed examination was made of the effects of potassium phosphate, 2,4‐DNP, KCN, and mCLAM on the respiration of beech mycorrhizas during ageing. Samples were taken on nine occasions during the year and aged for 9 days. Previous results were confirmed and it was shown that the cyanide‐insensitive pathway of oxygen uptake failed to develop fully if respiration was uncoupled. The application of cyanide seemed to allow phosphorylation to proceed at site 1 and in its presence the cyanide‐insensitive pathway could develop. Cyanide and DNP applied together caused considerable inhibition presumably owing to the small development of the cyanide‐insensitive pathway. The further addition of mCLAM gave additional inhibition. mCLAM appeared also to act as if it uncoupled phosphorylation from respiration, in addition to acting as an inhibitor of the cyanide‐insensitive pathway. It is suggested, since mCLAM does not uncouple mitochondrial oxygen uptake, that it is converted in the tissue to an uncoupling compound. The significance of the control of the insensitive pathway by phosphorylation or ATP level in the tissue is discussed.
THE LATE QUATERNARY HISTORY OF THE DIATOM FLORA OF LLYN CLYD AND LLYN GLAS, TWO SMALL OLIGOTROPHIC HIGH MOUNTAIN TARNS IN SNOWDONIA (WALES)
Authors: EVANS G. H. , WALKER R.
Published: May 2006

Three cores were taken from the deposits of Llyn Clyd and two cores from Llyn Glas, using a Mackereth corer. Samples taken at approximately 10 cm intervals have been analysed for pollen and diatoms. Pollen analysis has been used as a means for correlating deposits in the two tarns. The data show that changes have occurred in the diatom flora of both tarns but these changes are less pronounced than in some lowland bodies of water. Llyn Glas appears to have had more stable conditions throughout its development than Llyn Clyd.
STUDIES IN FESTUCA. 11. INTERRELATIONSHIPS OF SOME PUTATIVE DIPLOID ANCESTORS OF THE POLYPLOID BROAD‐LEAVED FESCUES
Authors: BORRILL MARTIN , KIRBY MADELEINE , MORGAN W. GARETH
Published: May 2006

The relationships of six diploid Festuca species were studied:

Section Montanae: F. donax, drymeja, altissima

Scariosae: F. scariosa

Bovinae: F. pratensis

Ovinae: F. polesica.

The criteria used were ability to hybridize, and fertility and meiotic chromosome pairing in the F1 hybrids. The closest affinity discovered was amongst the species within Section Montanae, there was also a strong affinity between these and F. scariosa, and a weak link with F. pratensis and F. polesica. The results are briefly discussed from the standpoint of species‐relationships in Festuca and Lolium.
ON THE THEORY OF EXPLOSIVELY DISPERSED SEEDS
Authors: BEER TOM , SWAINE M.D.
Published: May 2006

We calculate the theoretical distribution of seed numbers (a probability density function) that would be expected on the ground around a parent plant that disperses its seeds explosively. The initial velocity of the projected seed, and its air resistance are shown to have considerable influence on the maximum dispersal distance, as well as on the angle (the optimum angle of projection) which attains in. All other angles give rise to lesser dispersal distances and their relative frequencies contribute to the shape of the probability density function. The height of release has little influence on the maximum distance, but radically affects the shape of the probability density function. Some practical consequences and biological implications of these results are discussed.
EXPLOSIVE SEED DISPERSAL IN HURA CREPITANS L. (EUPHORBIACEAE)
Authors: SWAINE M. D. , BEER TOM
Published: May 2006

Methods are described for measuring the initial velocity, angular velocity, projection angle and air resistance coefficient of explosively dispersed seeds of Hura crepitans. The methods are generally applicable to any explosively dispersed seeds. In Hura the initial velocities were normally distributed about a mean of 43 ms−1 and in one case exceeded 70 m s−1. Although projection angles are not constant, the mean of 34° above horizontal lies close to the optimum for maximum dispersal, and the frequency of angles less than 0° or more than 50° are negligible. Angular velocities are high, attaining at least 15,000 rpm in one case. The resistance coefficient could not be measured precisely, but was probably between 0.087 and 0.118 m−1. The maximum dispersal distance recorded was 45 m from the parent tree, with a marked modal dispersal distance at about 30 m. The ecological implications of explosive dispersal are briefly discussed.
INFLUENCE OF MYCORRHIZAL INFECTION ON COMPETITION FOR PHOSPHORUS AND POTASSIUM BY TWO GRASSES
Authors: FITTER A. H.
Published: May 2006

Lolium perenne L. and Holcus lanatus L. were grown together in 125‐mm pots in a factorial experiment combining mycorrhizal infection and root competition. Both root competition and mycorrhizal infection gave a slight advantage to H. lanatus but, in combination, these produced considerable suppression of Lolium perenne. Root length of L. perenne was reduced by mycorrhizal infection, which was itself increased by competition. The competitive effects can be explained solely in terms of mycorrhizal infection.
THE EFFECT OF TIME OF EXPOSURE TO SULPHUR DIOXIDE ON POTASSIUM LOSS FROM AND PHOTOSYNTHESIS IN THE LICHEN, CLADINA RANGIFERINA (L.) HARM.
Authors: TOMASSINI F. D. , LAVOIE P. , PUCKETT K. J. , NIEBOER E. , RICHARDSON D. H. S.
Published: May 2006

Samples of the lichen, Cladina rangiferina, were exposed to various concentrations of aqueous SO4 for 10 min, and 0.5, 1, 3, 6 and 12 h. K+‐efflux curves (K+ release versus ppm SO2(wt/wt, aqueous)) were constructed for each exposure period. In separate experiments, the photosynthetic 14C fixation rates were measured after the SO2 exposures. Plots of % total 14C fixation v. ppm SO2 (wt/wt, aqueous) were found to be linear for the 3 h and 6 h exposure periods, while plots of log (% total 14C fixation) v. ppm SO2 (wt/wt, aqueous) were linear for shorter exposures (10 min, 0.5 and 1 h). Threshold SO2 concentrations for each exposure time were evaluated by extrapolating the K+‐efflux curves, or their linear transformations, to zero K+ release. Similarly, the threshold SO2 concentrations that did not cause a reduction in 14C fixation (relative to control samples not exposed to SO2) were determined by extrapolation of the linear relationships mentioned. The threshold values obtained from the K+‐efflux data were in good agreement with those evaluated from fixation rates. Aqueous threshold SO2 concentrations were converted to gaseous threshold values by an experimentally verified relationship. The resulting gaseous SO2 threshold concentrations, (SO2)g** in units of ppm(v/v) in air, were related to the exposure time in hours, t, through the following rectangular hyperbolic function: (SO2)g**=1.5 t−0.62. Notwithstanding the uncertainties involved, extrapolation of this expression to exposure times considerably longer than the experimental range yielded threshold values for 6 months and 1 year in good agreement with mean SO2 levels known from mapping studies to affect detrimentally sensitive lichen species.
A COMPARISON OF THE CHARACTERISTICS OF GLUTAMINE SYNTHETASE AND GLUTAMATE DEHYDROGENASE FROM LEMNA MINOR L.
Authors: STEWART G. R. , RHODES DAVID
Published: May 2006

The high affinity of Lemna minor glutamine synthetase for ammonium (Kappm 1.2 – 1.5 × 10−5 M) and its strong inhibition by ADP and 5‐AMP contrasts with the low affinity (Kappm 3 × 10−2 M) for ammonium and lack of inhibition by ATP shown by glutamate dehydrogenase. Glutamine synthetase was inhibited by alanine, aspartate, glycine and serine while glutamate dehydrogenase was not affected by any amino acid, other than the product of the reductive amination reaction, glutamate. The properties of glutamine synthetase and glutamate dehydrogenase are consistent with the view that the glutamine pathway is the major route for ammonia assimilation when there is a restricted availability of ammonia. The characteristics of glutamate dehydrogenase, when contrasted with those of glutamine synthetase, and considered in relation to the concurrent regulation of the two enzymes, support the view that the glutamate pathway may contribute towards ammonia assimilation under conditions of high ammonia availability or low energy charge. Comparison of the properties of glutamate dehydrogenase purified from ammonium‐ and nitrate‐grown plants suggests that only a single form of the enzyme is present.
PHYSIOLOGICAL‐ENVIRONMENTAL INTERACTIONS IN LICHENS
Authors: MACFARLANE J. D. , KERSHAW K. A.
Published: May 2006

The seasonal levels of nitrogenase activity in Peltigera praetextata and P. canina var. rufescens have been examined at 5, 10, 15, 20, 25, 30, 35°C, under 75, 150, 300 and 450 μEinsteins m−2 s−1 illumination and for all levels of thallus moisture content. The results show only a small increase in activity at high light intensities but a marked temperature optimum at 25–30 C in both species. Of outstanding interest however are the very large rate changes occurring throughout the year. The changes are clearly evident at all temperatures and light levels.

These results are discussed in relation to concurrent seasonal changes of net photosynthetic rate and the need for experimental design of physiological work in a multivariate framework is strongly emphasized.
PHYSIOLOGICAL‐ENVIRONMENTAL INTERACTIONS IN LICHENS
Authors: KERSHAW K. A. , DZIKOWSKI P. A.
Published: May 2006

The recovery rate of nitrogenase activity in Peltigera polydactyla, is shown to be rapid after short drought periods but takes progressively longer as the drought period is extended. After more extreme levels of dehydration achieved using calcium chloride, recovery of nitrogenase activity is considerably slower. The importance of adequate pretreatment of material collected from the field after exposure to unknown periods and levels of drought stress is emphasized.
LIGHT AS A FACTOR IN GROWTH AND MORPHOGENESIS I. EFFECT OF ARTIFICIAL SHADING ON CROTALARIA JUNCEA L. AND C. SERICEA RETZ.
Authors: PANDEY B. N. , SINHA R. P.
Published: May 2006

Two species of Crotalaria, C. juncea L., a fibre‐yielding plant, and C. sericea Retz., have been grown in a glasshouse at three different light‐intensities. Comparisons have been made of their rates of increase in dry weight, relative growth rate, leaf area ratio, specific leaf area, leaf weight ratio, net assimilation rate, the ratio a of Whitehead & Myerscough and shoot/root ratio. C. sericea appears to be the more shade‐tolerant because its increased leaf area ratio compensates for a reduced net assimilation rate and so maintains the level of its relative growth rate.
ANATOMICAL, PHYSIOLOGICAL, AND BIOCHEMICAL EVIDENCE FOR THE C3 PATHWAY IN VERBASCUM THAPSUS L.
Authors: WILLIAMS G. J. , KEMP P. R. , OULTON K.
Published: May 2006

Anatomical, physiological and biochemical characteristics of Verbascum thapsus demonstrate that this species is a C3 carbon fixation type rather than C4 as suggested by Parkhurst (1976). Leaf anatomy, net photosynthesis rate, carbon dioxide compensation point, photorespiration rate, temperature optimum for photosynthesis and ratio of ribulose‐1,5‐diphosphate carboxylase to phosphoenolpyruvate carboxylase activity for V. thapsus are all typical of C3 rather than C4 species. The data presented illustrate the danger of assuming a species is either C3or C4 based on a single characteristic. Parkhurst (1976) predicted that optimum photosynthesis for V. thapsus would occur at high temperature and would increase faster than transpiration with increased temperature. Our data are contrary to these predictions.
PRELIMINARY STUDIES ON SAPFLOW IN COCOS NUCIFERA L.
Authors: MILBURN JOHN A. , ZIMMERMANN MARTIN H.
Published: May 2006

A technique has been devised to study changes in the xylem‐sap tensions in Cocos using a pressure bomb. Preliminary studies indicate that xylem tensions range from 2 to 13 bar depending on solar radiation and other environmental changes. One surprising observation is that xylem sap tensions are somewhat lower in the dry season, apparently due to earlier stomatal closure during the mid‐late morning. Despite the close proximity of lagoons of saline water, there was no indication that the uptake of water was reduced through osmosis, and a hidden supply of fresh water is implied. Finally, some precautions are listed which avoid certain anomalous results using the pressure bomb.
FINE STRUCTURAL AND CYTOCHEMICAL CHANGES OCCURRING IN BEET DISCS IN RESPONSE TO WASHING
Authors: HALL J. L.
Published: May 2006

During washing of excised beetroot tissue discs the most prominent changes in fine structure were the development of amyloplasts and enhancement of the membrane systems of the Golgi bodies and endoplasmic reticulum. When D(‐)threo‐chloramphenicol was present during washing, the appearance of crystalloid bodies in the cytoplasm was accelerated. Staining with phosphotungstic acid‐chromic acid (PTAC) was largely restricted to the plasma membrane in freshly excised cells. After washing, additional PTAC staining was associated with the starch grains and with whorled arrangements of the plasma membrane close to the developing amyloplasts. Silver nitrate staining showed an intense particulate reaction in the vacuole and in the region of the tonoplast; the vacuolar staining was reduced in washed tissues. Biochemical analysis showed increased activities for both glucose‐6‐phosphatase and peroxidase. Cytochemical staining for glucose‐6‐phosphatase was localized largely in the plasma membrane and tonoplast in both fresh and washed tissues. Peroxidase staining was most prominent in the cell wall in freshly excised tissues. After washing, the reaction of the cell wall was increased and additional staining appeared associated with the Golgi bodies and endoplasmic reticulum. These findings are discussed in relation to the development of the wound response in plant tissues.
EARLY EFFECTS OF FLOODING ON NITROGEN DEFICIENCY AND LEAF CHLOROSIS IN BARLEY
Authors: DREW M. C. , SISWORO E. J.
Published: May 2006

Effects of flooding the root system on nitrogen status, leaf chlorosis and shoot growth have been studied in barley seedlings. Within 2 days, oxygen in the soil water decreased to a low concentration (< 2%), and net uptake of nitrogen to shoots was inhibited. Simultaneously, there was a decrease in the average concentration of nitrogen in shoots, due to translocation from older leaves to younger expanding ones. These changes pieceded the onset of chlorosis of the older leaves. It is suggested that inhibition of nitrogen uptake, and the consequent redistribution of nitrogen within the shoot, are important contributory factors in the early senescence of leaves and the retarded growth of shoots in flooded plants.
WOUND REPAIR IN YAM TUBERS: THE EFFECTS OF INHIBITORS OF RESPIRATION AND PROTEIN SYNTHESIS ON REPAIR PHYSIOLOGY
Authors: PASSAM H. C. , HUGHES P. A. , READ S. J.
Published: May 2006

The effects of inhibitors of respiration (KCN and salicylhydroxamic acid, SHAM) and of protein synthesis (cycloheximide and chloramphenicol) on the induction of wound respiration and acid invertase in bisected yam tubers and tissue discs are described. The respiration of tissue discs aged in tris‐HCl buffer increases markedly during 3 days following cutting. Respiration is largely insensitive to KCN. Inclusion of KCN or SHAM in the ageing medium inhibits the increase in respiration. Residual respiration is either sensitive to KCN when added to the Warburg vessel (SHAM‐aged) or insensitive (KCN‐aged). Ageing of discs in KCN + SHAM together, or in the presence of chloramphenicol, totally suppresses the induction of respiration. Ageing in the presence of cycloheximide increases the sensitivity of respiration to KCN. The same inhibitors were also applied to the cut surfaces of bisected, but otherwise intact, tubers for one hour after cutting. The respiration of the tubers increases after bisection, but the total respiration of the tuber halves is unaffected by inhibitor treatment. However, the increase in respiration measured in unaged discs taken from the surface starch/suberin layer is either inhibited (KCN, SHAM and chloramphenicol) or unaffected (cycloheximide) by treatment. The increase in respiration of the periderm is essentially unaffected by the inhibitors except for chloramphenicol which promotes. The induction of acid invertase activity in tissue discs following cutting, is inhibited to a varying degree by all treatments. In contrast, in the starch/suberin layer of bisected yams treated with KCN and/or SHAM the invertase activity is enhanced; chloramphenicol causes some inhibition, but cycloheximide has no effect. The development of invertase in the periderm is reduced by chloramphenicol but is unaffected by other treatments. In all treatments, activity in the corticular tissue (3 cm beneath the cut surface) remains low throughout the healing period. The results may largely be explained by the known metabolic effects caused by these inhibitors.
A LIGHT AND ELECTRON‐MICROSCOPICAL STUDY ON THE STRUCTURE AND FUNCTION OF THE SALT GLAND OF GLAUX MARITIMA L.
Authors: ROZEMA JELTE , RIPHAGEN INGRID , SMINIA TAEDE
Published: May 2006

The salt glands of Glaux maritima are regularly distributed on the adaxial and abaxial leaf surface. The gland consists of three cell types: a collecting cell, a stalk cell and secretory cells. The collecting cell is characterized by a large central vacuole, containing electron‐dense material. The stalk cell contains many small vesicles and is connected with both the collecting cell and the secretory cells by numerous plasmodesmata. The secretory cells possess a strongly infolded plasmamembrane (cell wall protuberances) which could facilitate rapid ion transport to the subcuticular space. The large number of mitochondria in the secretory cells suggests energy‐requiring steps in ion transport. The chloroplast‐free stalk cell and the secretory cells may be supplied with energy by transport across the numerous plasmodesmata. It is speculated that small (pinocytotic) vesicles are involved in ion transport in the salt gland.
A HISTOCHEMICAL STUDY OF POLYSACCHARIDE DISTRIBUTION IN EUCALYPT MYCORRHIZAS
Authors: LING‐LEE M. , ASHFORD A. E. , CHILVERS G. A.
Published: May 2006

This paper describes a histochemical study of the distribution of polysaccharides in un‐infected and mycorrhizal Eucalyptus fastigata roots. The most striking influence of mycorrhizal infection is the suppression of starch accumulation in the root cap cells and meristematic region of the root. In addition, there is a very substantial reduction in the amount of acidic polysaccharide (root cap slime) accumulated around the outer root cap cells in mycorrhizal roots, compared with uninfected roots. These observations generally hold for roots collected from a wide variety of conditions and at different times of the year. The reduction in amounts of these two important polysaccharides is presumed to result from lack of availability of precursors for polysaccharide synthesis, due to diversion of carbohydrate into the fungus partner. The histochemical observations in E. fastigata mycorrhizas are thus in accord with experimental data from other mycorrhizas which indicate transfer of large quantities of carbohydrate from root to fungus, and suggest that carbohydrate transfer is likely also to occur in mycorrhizas of E. fastigata.
ACETYLENE REDUCTION BY MATS OF BLUE‐GREEN ALGAE IN SUB‐TROPICAL GRASSLAND: POSSIBLE CONTRIBUTION BY OTHER MICRO‐ORGANISMS
Authors: JONES K.
Published: May 2006

Counts using the most probable number method show that there are aerobic and anaerobic nitrogen‐fixing bacteria associated with mats of blue‐green algae in kikuyu lawns. Both types of bacteria are more numerous in the surface layers of soil adjacent to the mats of algae. Acetylene reduction by bacteria was only detected when glucose was added to either the soils or the algal mats.

Mats of algae composed entirely of non‐heterocystous blue‐green algae were unable to reduce acetylene in situ or in any of the experimental conditions employed in the laboratory.
AN EARLY FLANDRIAN VEGETATIONAL RECORD FROM THE FLOOR OF THE BRISTOL CHANNEL
Authors: BROWN A. P.
Published: May 2006

A palynological and plant macrofossil study of a short core of organic sediment from the floor of the Bristol Channel at –36 m (–120 feet) O.D. is presented and discussed. The fossil assemblages were deposited in a freshwater pond and reedswamp. This sediment, the deepest yet examined for Flandrian pollen in the Bristol Channel, is overlain by what are interpreted as intertidal sediments and indicates the approximate sea level and position of the coastline of South Wales about 9500 years B.P. The open nature of the vegetation in the area around the site of deposition is indicated by the presence of Juniperus pollen. Of the only two tree pollen types present Betula is far more frequent than Pinus, a feature common to the early Flandrian of southwest England and northwest France. The age ascribed to this deep sediment is consistent with other observations on submerged deposits both in the Bristol and English Channels.
LEAF RESPIRATION AND ATP LEVELS AT CHILLING TEMPERATURES
Authors: WILSON J. M.
Published: May 2006

In the extremely chill‐sensitive species Episcia reptans the dark respiration rate of leaves after 80 min chilling at 5°C was three times greater than in leaves maintained at 25°C. The rate and size of the respiratory increase depended on the chilling temperature and the growth conditions prior to chilling and was at a maximum at the same time as the onset of visible injury. The addition of 2,4‐dinitrophenol and potassium cyanide to the leaves of E. reptans accelerated the rate of oxygen uptake at 5°C. In contrast, there was no increase in the respiration rate of the leaves of the less chill‐sensitive species Phaseolus vulgaris after prolonged chilling at 5°C.

A reduction in ATP supply below that necessary to maintain the metabolic integrity of the cytoplasm is not considered to be important in the development of chilling‐injury to Episcia reptans or Phaseolus vulgaris as the ATP level decreased only after the onset of visible leaf injury. Furthermore, the increase in ATP level on chilling P. vulgaris leaves which had been either chill‐hardened or maintained in a saturated atmosphere on transfer from 25 to 5°C (Wilson, 1976) demonstrated that leaf injury and water stress are the primary cause of the decline in ATP level during chilling and not low temperature per se.
CARBON SOURCE FOR DEVELOPING BOLLS IN NORMAL AND SUPEROKRA LEAF COTTON*
Authors: HORROCKS R. D. , KERBY T. A. , BUXTON D. R.
Published: May 2006

Narrow‐row field experiments were conducted to investigate the importance of leaves near developing bolls as a source of assimilate in normal and superokra leaf cotton (Gossypium hirsutum L.) plants. A small plexiglass chamber was used to enclose individual leaves which were pulsed with 14CO2 for 5 min. Leaves were labelled when sink bolls were 10 days old. Despite much smaller leaves at each position (averaging 42% of normal leaf size) the superokra leaves exported similar amounts of 14C‐assimilate to the primary boll as did normal plant leaves. Primary sympodial bolls of superokra and normal leaf plants received 37 and 41% of their 14C‐assimilate from subtending leaves, respectively, 38% from the secondary sympodial leaf, and 28.2 and 21.5%, respectively, from the main stem leaf. Although the leaf subtending the boll of superokra plants was much smaller than the subtending normal leaf, the amount of assimilate provided to the boll was 88% of the normal leaf. The differences in assimilate export to a given boll may not be as important in causing fruit abortion in superokra cotton as expected from leaf size considerations.
CHANGES IN THE ETHANOL‐SOLUBLE CARBOHYDRATE COMPOSITION AND ACID INVERTASE IN INFECTED FIRST LEAF TISSUES SUSCEPTIBLE TO CROWN RUST OF OAT AND WHEAT STEM RUST
Authors: MITCHELL D. T. , FUNG A. K. , LEWIS D. H.
Published: May 2006

Monosaccharides, sucrose and acyclic polyols in healthy and infected first leaves of oat and wheat susceptible to crown rust and stem rust respectively were quantitatively determined. In oat tissues heavily infected with crown rust (thirty‐four lesions/cm segment), sucrose and reducing sugars increased during flecking and then declined. During sporulation of wheat stem rust‐infected tissues, sucrose levels at an infection intensity of eight lesions/leaf were greater than those of comparable healthy tissues whereas, at a higher infection intensity (107 lesions/leaf), there was a slight decline in sucrose with increases in both fructose and glucose. Soluble sugars (combined sucrose, fructose and glucose) were greater in the ‘pustule area’ compared with ‘region adjacent’ on the same leaf of wheat. Activity of acid invertase in infected tissues is related to infection intensity in crown rust of oat. However, in wheat stem rust infected tissues, a stimulation of acid invertase only occurred during the appearance of definite type 4 lesions. At the sites of infection, there were increases in mannitol and arabitol during flecking and sporulation, and a direct correlation between acyclic polyol levels and numbers of erupted lesions/leaf.
ORIGIN OF THE QUIESCENT CENTRE IN ZEA MA YS
Authors: CLOWES F. A. L.
Published: May 2006

Establishment of the quiescent centre has been studied in embryogeny, in development of lateral root primordia and in roots regenerating after decapitation. In embryos a quiescent centre first appears just after the oblique root‐shoot axis becomes discernible, as soon as a cap meristem forms at the root pole and then again during the early stages of germination of seeds. In lateral primordia a quiescent centre also arises twice; once while the first set of cap initials, which are of endodermal origin, is functioning and then after they have ceased operating when new cap initials of pericyclic origin have replaced them. The first quiescent centre exists while the primordium is still embedded in the mother cortex, but the second can occur either before or after emergence from the mother root. In regenerating roots a quiescent centre establishes itself when a cap meristem becomes transiently distinct from the rest of the meristem by a difference in planes of cell growth and division. This happens before the meristem acquires the characteristic cell pattern of a normal grass root.

These observations are discussed in relation to the reasons for the existence of quiescent centres to root meristems.
AGEING‐LINKED CHANGES IN PHOTOSYNTHETIC CAPACITY AND IN FRACTION I PROTEIN CONTENT OF THE FIRST LEAF OF PEA PISUM SATIVUM L.
Authors: GORDON K. H. J. , PEOPLES M. B. , MURRAY D. R.
Published: May 2006

Pea seedlings (Pisum sativum L. cv. Melbourne Market) were grown under light‐limited conditions (12 h photoperiod of 1 klx; 19°C) so that both the development and senescence of the first true leaf could be studied within a period of 4 weeks from the beginning of germination. Rapid cell expansion and synthesis of protein and chlorophyll occurred between days 8 to 12. Whereas photosynthetic O2 evolution and RuBP carboxylase both showed maximum values per leaf at 16 days, declining thereafter, that of NADH:glyoxylate reductase, a peroxisomal marker, occurred between 11 and 14 days and was decreasing by 16 days. Total leaf ribose‐5‐P isomerase activity increased two‐fold to a maximum at 14 days then fell sharply before 16 days. Dark O2 uptake by leaf slices and NADH oxidase activity showed extended maxima from the earliest stages to 20 and 16 days respectively. Soluble acid phosphatase also showed an extended period of maximum activity per leaf, from 12 to 21 days, then declined slowly.

As a proportion of leaf soluble protein, Fraction I protein varied from 17% (day 8) to 41% (day 10), 57%(day 14), 76%(day 16) then to about 60% from day 21 onwards. Between 14 and 16 days the amount of Fraction I protein in the leaf continued to increase, although the amount of total soluble protein had begun to decline. Aminopeptidase (leucyl β‐naphthylamidase) activities per leaf also began to decline after 14 days. Since the maximum photosynthetic capacity of the leaf is not observed until 16 days, the data indicate the onset of leaf senescence prior to the completion of chloroplast development.
ANATOMY, HISTOCHEMISTRY AND CYTOLOGY OF DORMANT AND STRATIFIED APPLE EMBRYOS
Authors: DAWIDOWICZ‐GRZEGORZEWSKA ALINA , LEWAK ST.
Published: May 2006

Changes in the anatomy and cytology of apple embryos isolated from seeds during after‐ripening (3‐month stratification at +4°C)were investigated. Structural changes differed in cotyledons and embryo axes. In cotyledons they were limited to stepwise differentiation of the vascular tissue, whereas the structural alterations in axes were related to starch accumulation. A general increase of starch up to the end of after‐ripening was noted after a temporary decrease during the first 10 days of stratification. Accumulation of starch during the third month of after‐ripening was restricted to the limit zone between the radicle and hypocotyl. Starch accumulation (followed by degradation) was localized in a zone corresponding to that in which cell elongation begins. The structural changes were correlated with the metabolic changes known to occur during the after‐ripening of apple seed.
A STUDY OF THE EXTRAFLORAL NECTARIES OF RICINUS COMMUNIS
Authors: BAKER D. A. , HALL J. L. , THORPE J. R.
Published: May 2006

A study has been made of the fine structure and exudate composition of the extrafloral nectaries of Ricinus communis. Actively secreting glands were characterized by the presence of well‐developed swollen endoplasmic reticulum, numerous vesicles, ribosomes and mitochondria, and the occurrence of crystalline (protein) bodies in the nucleus and cytoplasm. Golgi bodies were not prominent. The gland exudate differed from the phloem exudate in a number of respects, particularly in the much lower levels of amino acids and phosphate and the presence of glucose and fructose. Plants with glands removed showed no difference in growth from the untreated controls. The findings are discussed in relation to the possible functions of extrafloral nectaries.
15N INCORPORATION AND GLUTAMINE SYNTHETASE INHIBITION STUDIES OF NITROGEN ASSIMILATION IN LEAVES OF THE NITROPHILE, DATURA STRAMONIUM L.
Authors: LEWIS O. A. M. , PROBYN T. A.
Published: May 2006

The N assimilation pathways in leaves of Datura stramonium L. have been investigated at low and high levels of xylem stream nitrate feeding by an 15N infiltration technique in the presence and absence of the glutamine synthetase inhibitor, methionine sulphoximine (MSO).

In the absence of MSO, glutamate showed the highest 15N enrichment of any free amino compound at both feeding levels. At the high N feeding level, glutamine showed the highest accumulation of 15N at all stages of the time course, with secondary accumulation in glutamate. At the low N feeding level the reverse was true. These findings indicate the operation of both the glutamine synthetase‐GOGAT and glutamate dehydrogenase pathways in Datura leaves.

In the presence of MSO intracellular pools of all the amino compounds, with the exception of glutamine and threonine, became rapidly drained. There was an almost complete restriction of the supply of newly reduced 15N to amino acid assimilation and it accumulated as ammonia. The large glutamine pool remaining contained no 15N enrichment, and was probably an extrachloroplastic storage pool not immediately available for amino acid synthesis. These experimental results indicate the almost exclusive role of the glutamine synthetase‐GOGAT pathway in the assimilation of newly reduced nitrate into amino acid metabolism in Datura leaves.
YIELD PERFORMANCE OF MIXTURES OF OATS AND BARLEY
Authors: BEBAWI F. F. , NAYLOR ROBERT E. L.
Published: May 2006

Four experiments were conducted to compare the yield, and stability of yield of oats and barley grown separately and in an equiproportional mixture (w/w). The cultivars used were Maris Mink and Karin, chosen to synchronize, as far as possible, their maturity dates. In general, the mixtures marginally overyielded the more productive species but not significantly so. When barley was sown at half field density, grain yield did not drop. In contrast, the yield of oats was lower when plots were sown at lower density. Barley was generally more unstable in its yield than oats, which it outyielded on good sites but underyielded on poor sites. Mixtures were much more stable than barley, and almost as stable as oats, but were never the most stable type of plot.
THE GENECOLOGY OF LAWN WEEDS
Authors: WARWICK S. I. , BRIGGS D.
Published: May 2006

An examination of variation in Poo. annua L. provided evidence for population differentiation between two bowling greens and their adjacent flower beds. The bowling green populations consisted almost entirely of prostrate individuals, whereas the flower bed populations were more heterogeneous, containing both erect and prostrate growth forms.

Family trials indicated that vegetative and floral erectness, and time from sowing to anthesis were under genetic control. Erect families came into flower significantly quicker than prostrate families. Moreover, there were significant differences, both between and within families, for each of the two growth forms in mean number of days from sowing to anthesis.

An investigation was conducted using gel electrophoretic techniques to examine the genetic structure of these populations of P. annua, and to estimate the amount of natural out crossing. The esterase enzyme system was found to consist of multiple molecular forms. No apparent banding differences were found which distinguished erect and prostrate growth forms. Heterogeneity of banding patterns was discovered within both growth form groups, suggesting that each of the prostrate and erect growth forms consisted of more than one genotype. Evidence that the observed banding patterns were under genetic control was obtained from the examination of four families derived from selfed heterozygotes, which yielded segregating patterns within families.

Both erect and prostrate growth forms, in the area under study, had the chromosome number 2n= 28.
THE ADAPTATION OF CALLUNA VULGARIS (L.) HULL TO CONTRASTING SOIL TYPES
Authors: MARKS R. H. , BANNISTER P.
Published: May 2006

Samples of Calluna vulgaris were collected from several sites of contrasting soil type and the mineral status of plants and soils measured. Differences in the concentrations of several potentially toxic elements in these plants and soils occurred but the nitrogen, potassium and phosphorus concentrations, particularly in the plants, were similar. When cuttings of Calluna from each population were grown in all soil types, it was shown that these samples were adapted to the different soils. Two ways in which this species may be adapted to tolerate high concentrations of lead were noted.
AN INTERGLACIAL DEPOSIT AT SCANDAL BECK, N.W. ENGLAND
Authors: CARTER P. A. , JOHNSON G. A. L. , TURNER J.
Published: May 2006

A lacustrine deposit with included peat was discovered beneath till at Scandal Beck, Cumbria. A pollen diagram from the organic layers has three pollen assemblage zones which cover the last part of an interglacial. It is argued that the deposit most probably dates from the Ipswichian.
UPPER CRITICAL LEVELS OF TOXIC ELEMENTS IN PLANTS
Authors: DAVIS R. D. , BECKETT P. H. T.
Published: May 2006

Though the concentration of Cu, Ni or Zn in the tissue of young (five‐leaf) spring barley grown in a nutrient solution containing one of these elements varies considerably with the growing conditions, the minimum concentrations of Cu, Ni or Zn in plant tissue (Cu 19, Ni 12, Zn 210 ppm dry wt) necessary to cause toxic reactions are relatively independent of the growing conditions. The values for ryegrass S.23 are very similar (Cu 21, Ni 14, and Zn 221 ppm), as are the Cu values for lettuce, rape and what (21, 16 and 18 ppm respectively). At higher concentrations of these elements in plant tissue yield is reduced approximately in proportion to log (tissue concentration).

The application of these observations to a procedure for monitoring environmental pollution, outlined in an earlier paper, is further developed.
TOLERANCE OF TREE ROOTS TO WATERLOGGING
Authors: COUTTS M. P. , PHILIPSON J. J.
Published: May 2006

Rooted cuttings of Sitka spruce and Lodgepole pine were grown in Perspex tubes of peat and the lower portion of the root systems was flooded, while either active or dormant, and at 6° and 15°C. Root survival was assessed after draining the tubes.

Root elongation in both species stopped within a few days of flooding, during which the oxygen flux in the peat had declined to zero. Actively growing root tips were more susceptible to waterlogging than the region behind the tip and the latter region remained alive for up to 90 cm below the water‐table in certain treatments.

Growing roots of pine were more tolerant to waterlogging than spruce, when assessed in terms of the survival of both the tip and the basal region of the root. By contrast, dormant roots of both species were so tolerant to waterlogging that the tips remained alive and rapid regrowth took place after the soil was drained.
FACTORS AFFECTING ABSCISSION IN SPIRODELA OLIGORHIZA (LEMNACEAE)
Authors: WITZTUM A. , KEREN O.
Published: May 2006

0.1 M and 0.2 M sucrose do not induce abscission and significantly reduce abscission induced by ultraviolet radiation whereas higher concentrations (0.4 M) induce abscission even without UV radiation. The effect of different concentrations of sucrose on endogenous ABA levels and on ethylene release suggest that sucrose‐induced abscission occurs when ethylene release is accompanied by a rise in the endogenous ABA level. When plants are floated on low concentrations of ABA (0.1 ppm), they release a considerable amount of ethylene but do not abscise. On higher concentrations of ABA (10 ppm), they abscise, even though ethylene release is lower.
LIPID METABOLISM OF LEAVES OF POA PRATENSIS DURING INFECTION BY PUCCINIA POARUM
Authors: LÖSEL D. M.
Published: May 2006

During the development of the uredial and telial stages of the rust, Puccinia poarum, on leaves of Poa pratensis, lipid accumulates in and around the infected tissues to a level more than double that of uninfected leaves. Microscopically, the infection on Poa differs from that on the alternate host, Tussilago furfara, in the less extensive development of fungal tissue, the much more frequent occurrence of haustoria and the greater amount and persistence of lipid globules in host cells. Urediosori contain significantly more triglyceride and sterols than healthy tissue and teliosori contain more neutral lipid of all classes. As on Tussilago. there was a rapid disappearance of chloropiast glycolipids and phosphatidyl glycerol in the early phases of growth on Poa, accompanied by increases in phosphatidyl choline, phosphatidyl ethanolamine and phosphatidyl serine, which are attributed primarily to synthesis of fungal membrane lipids.
METABOLIC POOLS IN THE SPADIX OF ARUM DURING FLORAL DEVELOPMENT
Authors: WEDDING RANDOLPH T. , BLACK M. KAY , HARLEY JOHN L.
Published: May 2006

The concentration of certain metabolic intermediates in the spadix of Arum has been determined over the complete period of floral development from the point at which the spathes are first visible in the leaf base to thermogenesis in the spadix. These intermediates include sucrose, glucose, fructose, pyruvate, alanine, citrate, α‐ketoglutarate, glutamate, glutamine, malate, aspartate and asparagine. Assays for these intermediates were supplemented by measurements of mitochondrial respiratory activity, soluble and protein‐bound flavins, thiamine and ethanol‐insoluble materials.

These constituents and processes reveal four broad patterns of change indicating a complex system controlling floral development and thermogenesis. The clearest indication of a specific control seen is the correlation of low mitochondrial respiratory activity with low levels of soluble flavins, suggesting that lack of these cofactors limits the respiratory activity of young spadices.
THE EFFECT OF SIMAZINE ON THE GROWTH AND RESPIRATION OF A CELL SUSPENSION CULTURE OF CELERY
Authors: METCALF E. C. , COLLIN H. A.
Published: May 2006

Celery cell suspension cultures, inoculated into liquid medium containing simazine and maintained for 3 weeks, showed little growth and low respiratory activity at concentrations of 1.0 and 10.0 mg 1−1 simazine but growth and respiration were normal with 0.01 and 0.1 mg 1−1 simazine. The addition of 1.0 or 10.0 mg 1−1 simazine to a cell culture caused an immediate stimulation of respiration rate; lower concentrations of simazine were ineffective. The initial high respiratory rate in 10 mg 1−1 simazine was not maintained and after 6 h the rate had declined to the level of the control. When the cells were incubated in 10 mg 1−1simazine for a longer period the rate declined to zero after 1 week, cell division was inhibited and the dry weight decreased. The initial high rate of respiration in simazine, followed by a decline, combined with the inhibition of growth and finally cell death suggested that the simazine may be acting as a respiratory uncoupler.