bluuebunny/crossref_metadata_2025 huggingface dataset:
THE FINE STRUCTURE OF A PERITAPETAL MEMBRANE INVESTING THE MICROSPORANGIUM OF PINUS BANKSIANA
Authors: DICKINSON H. G.
Published: May 2006

Summary

An acetolysis‐resistant membrane develops around the microsporangium of Pinus banksiana while the pollen mother cells are undergoing meiosis. The formation of this membrane appears to involve the deposition and polymerization of sporopollenin precursors upon a primary layer believed to be lipid. The source of both these components is considered to be the tapetum and attention is drawn to the similarity in construction between this membrane and the tapetal orbicules. Possible functions of the membrane in the development and dispersal of the pollen are discussed.
STUDIES ON THE LIGNOTUBERS OF EUCALYPTUS OBLIQUA L'HERI.
Authors: CARRODUS B. B. , BLAKE T. J.
Published: May 2006

Summary

The anatomy of lignotubers of a eucalypt are examined and the distribution and amount of storage tissue discussed. The relative amounts of carbohydrates held in the lignotubers and adjacent root and stem are examined. It is concluded that the lignotuber is no more efficient than the root or stem as storage tissue, and that its prime function is probably related to the large number of buds it holds in a protected position.
THE EFFECTS OF SYCOPHAGA SYCOMORI L. ON THE STRUCTURE AND DEVELOPMENT OF THE SYNCONIA IN FICUS SYCOMORUS L. *
Authors: GALIL J. , DULBERGER R. , ROSEN D.
Published: May 2006

The anatomy of the syconia and flowers in the sycomore fig (Fiats sycomorus) has been studied. The developmental course of the ovules and pollen grains and their ultimate structure were found to be normal. No difference was detected between short‐ and long‐styled flowers. In the Mediterranean area, Sycophaga sycomori is the principal sycophilous wasp developing within the ovaries of the sycomore. The wasp inserts its egg into the embryo sac via the style. Inhabited but unfertilized syconia which do not contain plant embryos persist on the tree and continue to develop, while the unoccupied syconia drop within a few days. Inhabitation by the wasp has a decisive effect on the subsequent development of the syconia and flowers. Oviposition induces sclerification of the pericarp and proliferation of the nucellus, which serves as‘feeding’ tissue for the insect larva. Inhabitation by Sycophaga is indispensable for the maturation of the male flowers. Uninucleate pollen grains were the final stage attained in uninhabited syconia.
LIME CHLOROSIS AS A FACTOR IN SEEDLING ESTABLISHMENT ON CALCAREOUS SOILS
Authors: HUTCHINSON T. C.
Published: May 2006

The water relations of a number of species affected by lime‐chlorosis have been studied by following the development of leaf water deficits in detached leaves gravimetrically. It has been found, both for material collected in the field and for material raised under controlled laboratory conditions, that chlorotic leaves invariably lose water more rapidly than do green leaves of the same species. The rate of transpirational loss of individuals of a species is directly related to the degree of chlorosis they exhibit. Addition of iron chelate to soil in which a chlorosis‐susceptible plant grows alleviates the chlorosis and the rate of transpiration is also greatly reduced. The age of the material and intrinsic soil factors also influence rates and patterns of transpirational loss. Both the stomatal and cuticular phases of transpiration appear to be affected in chlorotic material, where the larger leaf water deficits may be due either to more rapid loss during the stomatal phase, coupled with later stomatal closure, or to more rapid cuticular loss, or both. The percentage of dry matter in chlorotic leaves is reduced compared with that in green leaves. The ecological significance of the overall findings is discussed in relation to the potential survival of species invading calcareous soils as seedlings. Such seedlings are very often subjected to annual droughts.
METABOLIC CHANGES OF POLYAMINES DURING THE GERMINATION OF PHASEOLUS VULGARIS
Authors: BAGNI N.
Published: May 2006

The distribution and changes in spermine and spermidine during the germination and seedling growth of bean (Phaseolus vulgaris) were investigated. The results show in vivo a substantial parallelism between RNA and protein changes and polyamine changes during germination. Spermine and spermidine diminish in the cotyledons and increase in the shoots especially the epicotyls. The data concerning in vitro cultures of isolated cotyledons and embryos show that there is a dc novo synthesis of spermine and spermidine in the seedlings particularly in the light. Although the greater part of the polyamines are translocated from cotyledons to embryo and afterwards into the different parts of the growing seedling, some is degraded. It is concluded that synthesis and translocation of such compounds during germination can be compared with an analogous pattern of RNA and protein changes.
PHOSPHATE ABSORPTION BY PLANTS FROM HABITATS OF DIFFERENT PHOSPHATE STATUS
Authors: NASSERY H.
Published: May 2006

Whole plants of Urtica and Deschampsia of different phosphate status were used to study phosphate uptake. By contrast with excised roots, the attached roots of the plants showed differences both in the rate of uptake and their patterns of incorporation of phosphate. The rate of phosphate absorption from low concentrations was rather similar for the two species, but from high concentrations, Urtica absorbed at a greater rate. A greater proportion of the absorbed phosphate was incorporated into acid insoluble and acid soluble organic phosphate in Urtica than in Deschampsia. Urtica is more sensitive to phosphate concentration in its total growth rate relative shoot and root growth, and in total uptake than Deschampsia.
THE EFFECTS OF WATER STRESS ON NITROGEN‐FIXING ROOT NODULES
Authors: SPRENT JANET I.
Published: May 2006

Summary

When the fresh weight of detached soybean nodules is reduced below 80% of its maximum (fully turgid) value, irreversible changes occur. Acetylene and nitrogen reducing activities cease, respiratory rates become very low and there are gross structural changes. Such nodules are probably shed by the plant.

Reduction of water content down to 80% of the maximum fresh weight, leads to a proportionate slowing down of acetylene reduction, with a concomitant reduction in respiratory activity.
PLANT GROWTH RESPONSES TO VESICULAR‐ARBUSCULAR MYCORRHIZA
Authors: HAYMAN D. S. , MOSSE B.
Published: May 2006

Summary

Onion and Coprosma plants were grown in a range of soils mostly containing very little available phosphate. Very large increases of shoot dry weight (up to eighteen‐fold with Coprosma and nineteen‐fold with onion) were obtained by adding phosphate. Similar increases (up to fifteen‐fold with Coprosma and twelve‐fold with onion) were obtained by mycorrhizal inoculation. The response to phosphate equalled or slightly exceeded the response to mycorrhiza, except in two soils rich in phosphate in which there was no response to either, and in one soil in which the mycorrhizal onion and Coprosma plants were twice as heavy as those given phosphate. The greatly increased growth from either treatment was associated with a large increase in the uptake of phosphorus. The probability of such growth responses, but not their size, was usually predictable in soils containing very little phosphorus soluble in CaCl2. In all soils with inoculum mycorrhizal infection was extensive. The sources of phosphorus available to mycorrhizal roots but not to non‐mycorrhizal roots differed in the various soils. In some inhibitory factors might make vesicular‐arbuscular mycorrhiza less effective in promoting the growth of the host plants.
PERFECT STATES OF RHIZOCTONIAS ASSOCIATED WITH ORCHIDS. II
Authors: WARCUP J. H. , TALBOT P. H. B.
Published: May 2006

Summary

Further Rhizoctonia isolates obtained from Australian orchids have been induced to fruit in culture. The perfect states thus obtained include Tulasnella allantospora Wakefield and Pearson, T. violea (Quélet) Bourdot and Galzin, and two new species, T. cruciata and Ceratobasidium sphaerosporum. The description of Tulasnella asymmetrica is emended.
ROUTINE ANALYSIS BY GAS–LIQUID CHROMATO‐GRAPHY OF SOLUBLE CARBOHYDRATES IN EXTRACTS OF PLANT TISSUES
Authors: HOLLIGAN M.
Published: May 2006

Summary

The general principle of gas–liquid chromatography, and the types of column packing and volatile derivative available for the analysis of carbohydrate are discussed. Techniques for the separation of soluble sugars from plant tissues as the trimethylsilyl and acetate derivatives are evaluated, with special refernce to the problems of resolution and peak identification. Finally, various aspects of quantitative gas–liquid chromatography are considered.
A METABOLIC THEORY OF FLOODING TOLERANCE: THE SIGNIFICANCE OF ENZYME DISTRIBUTION AND BEHAVIOUR
Authors: MCMANMON M. , CRAWFORD R. M. M.
Published: May 2006

Summary

The distribution and activity patterns of several enzymes of glycolytic and respiratory metabolism are considered in nineteen species of higher plants previously classified as tolerant or intolerant of experimental flooding. These results are combined with previous work on glycolysis, the inductive properties of alcohol dehydrogenase, and on tissue malic acid levels, to formulate a metabolic system of flooding tolerance. This system is based mainly on: (1) the control of glycolysis through the inductive and kinetic properties of alcohol dehydrogenase; and (2) a diversion from ethanol to malate accumulation, dependent upon the presence or absence of ‘malic’ enzyme.
THE LIFE‐CYCLE OF PLASMODIOPHORA BRASSICAE WORON. IN BRASSICA TISSUE CULTURES AND IN INTACT ROOTS
Authors: TOMMERUP INEZ C. , INGRAM D. S.
Published: May 2006

Summary

The life cycle of Plasmodiophora brassicae was studied in stained preparations of Brassica napus and B. rapa callus tissue cultures and clubbed roots. Resting spores germinated in situ in callus cells to produce naked protoplasts which underwent plasmogamy to form multinucleate primary plasmodia. Mitosis then occurred and was followed by cleavage of the plasmodia into zoosporangia containing uninucleate zoospores. The zoospores were released and fused in pairs (without karyogamy) and then penetrated living callus cells where growth and mitosis took place to give multinucleate secondary vegetative plasmodia. The vegetative plasmodial nuclei fused in pairs and then underwent meiosis immediately. This was followed by cleavage of the plasmodial cytoplasm to yield uninucleate, haploid resting spores. P. brassicae had a haploid chromosome number of five in both 2‐year‐old callus cells and in recently harvested club‐root tissues.
EFFECT OF CANE SUGAR ON THE UPTAKE OF CHLORIDE BY DISCS FROM CARROT ROOT
Authors: BRIGGS G. E.
Published: May 2006

Summary

The exosmosis and reabsorption of electrolytes by freshly cut discs is retarded by the presence of 0.2 M and 0.02 M cane sugar. The presence of cane sugar during pre‐treatment of freshly cut discs depresses the uptake of chloride when they are transferred to 0.01 M KCl; the presence during the uptake by discs pretreated in water causes an increase in the uptake of chloride; these effects are probably additive when the sugar is present during pre‐treatment and uptake.
A STUDY OF THE ROOT SYSTEM OF BARLEY
Authors: HACKETT C. , BARTLETT B. O.
Published: May 2006

Summary

The lengths of branched and unbranched axis, the density of branching, and the change in length of laterals along the axis (called the root profile) were determined on roots of Maris Badger and Proctor barley (Hordemn vulgare L.) grown in water culture under complete nutrient supply and deficiencies of potassium and phosphorus.

The most striking observations were (a) 50–75% reductions in the length of unbranched axis caused by nutrient deficiency, (b) marked curvilinearity in the profile under all nutrient treatments, and (c) high dependency on the form of the profile on variety and nutrition.
NITROGENASE ACTIVITY IN WISCONSIN LAKES OF DIFFERING DEGREES OF EUTROPHICATION
Authors: STEWART W. D. P. , MAGUE T. , FITZGERALD G. P. , BURRIS R. H.
Published: May 2006

Summary

Nitrogen fixation in various Wisconsin lakes was compared using the C2H2 reduction technique. Rates of C2H2 reduction were unaffected by N2 when sufficient C2H2 was added to the gas phase. Thus in field studies the natural gas phase need not be removed before the addition of C2H2. C2H2 was reduced rapidly in eutrophic waters (Little Arbor Vitae Lake, Lake Mendota and southern Green Bay) but more slowly in oligotrophic waters (Crystal Lake, Trout Lake, Lake Mary and northern Green Bay). C2H2 reduction was greatest in the surface waters, was largely light‐dependent and showed a marked diurnal variation. There was also significant variation with area and with time, and in general acetylene reduction was detected only when heterocystous algae were present. The rate of nitrogen fixation in Lake Mendota, calculated on the basis of weekly measurements taken during most of the ice‐free season, was approximately 2.4 kg/ha/year.
CHANGE OF APPARENT WEIGHT OF PLANT TISSUES IN SOLUTION
Authors: BLYTH D. F. , BRIGGS G. E.
Published: May 2006

Summary

If there is any active transport of water between plasrnolysed cells of carrot root and the plasmolyticum the respiratory regulators potassium cyanide and methylene blue have a negligible effect on it. With 0.5 M KNO3 and 0.7 M cane sugar the changes in the apparent weight in the presence of these regulators relative to that in their absence is probably due to effects on the change of solutes in the tissue.
A POLLEN DIAGRAM FROM QUINCAN CRATER, NORTH‐EAST QUEENSLAND, AUSTRALIA
Authors: KERSHAW A. P.
Published: May 2006

Summary

Pollen analytical results from the organic sediments of Quincan Crater broadly confirm the sequence of vegetation changes indicated in a previous study at Lake Euramoo. Only the later stage of the transition from sclerophyll vegetation to ‘warm temperate’ rain forest, culminating about 6000 B.P., is represented at Quincan, but indicates that the change was most probably due to an increase in effective precipitation. Afterwards rain forest remained the principal vegetation type for 3000 or 4000 years but changed from the initial ‘warm temperate’ to a ‘subtropical’ kind probably as a result of an increase in temperature and possibly also of precipitation. At about 2000 B.P. the ‘subtropical’ rain forest assumed a ‘drier’ facies and there was a partial readvance of the sclerophyll vegetation.
ULTRASTRUCTURAL CHANGES IN CHLOROPLASTS OF PHASEOLUS VULGARIS DURING DEVELOPMENT UNDER CONDITIONS OF NUTRIENT DEFICIENCY
Authors: WHATLEY JEAN M.
Published: May 2006

Summary

Plants of Phaseolus vulgaris were grown for a period of 4 weeks in nutrient solutions deficient in S, Mg, K, N, P and Fe, and compared with controls growing in complete nutrient solutions. At weekly intervals, tissue from all leaf groups fully expanded at the time of sampling was prepared for examination under the electron microscope. It was possible to examine chloroplast ultrastructure, firstly, during leaf development under each of the nutrient deficient conditions and, secondly, to compare the chloroplasts of similar leaf groups produced under different deficiency conditions. Although distinctive chloroplast types could be associated with conditions of Mg, K, N and Fe deficiency, chloroplasts from S and P deficient plants were variable in appearance. The chloroplast patterns produced were found to be consistent in palisade parenchyma tissue but in spongy mesophyll tissue cells frequently appeared plasmolysed and chloroplasts varied considerably in appearance. Particularly in the spongy mesophyll distinctive crystalline configurations were found within the chloroplasts.
PHYSIOLOGICAL‐ECOLOGY OF XANTHIUM STRUMARIUM LINN.
Authors: KAUL V.
Published: May 2006

Summary

There are various forms within the species which exhibit a differential seasonal behaviour. These have been designated as ‘monsoon’, ‘winter’, ‘winter‐summer’ and ‘summer’ forms. The life cycle of the ‘monsoon form’ starts under a high temperature regime and finishes under low temperature. The ‘winter’, ‘winter‐summer’, and the ‘summer’ forms grow in constant low temperature, an initial low temperature terminating in a high temperature and in constantly‐high temperature regimes respectively. The critical photoperiod for these forms ranges from 13 hours' duration to continuous light. The species does not grow at all in shaded localities. Many of the differentiating characters, however, become slightly less distinct when the different forms are raised together under a similar set of conditions in one or the other season, and this suggests that they originated from a common stock and evolved in response to environmental differences (as has been suggested for the various American species of Xanthium). The origin of the species with regard to its varying critical photoperiod has been discussed.
ENDOGENOUS STOMATAL MOVEMENTS IN TRADESCANTIA VIRGINIANA
Authors: MARTIN E. S. , MEIDNER H.
Published: May 2006

Summary

The stomata of Tradescantia virginiana undergo rhythmic changes in aperture in either continuous light or darkness. Whilst these changes persist for several days in continuous light, in darkness the rhythm damps after one cycle. In continuous light the rhythm was characterized by susceptibility to phase‐shift and by a period of approximately 24 hours. In continuous darkness the single opening cycle was also susceptible to phase‐shift depending upon the timing of the previous light treatment. Stomatal opening and closing in response to short light‐dark treatments could be superimposed upon the endogenous rhythm.
INORGANIC NUTRITION OF THE PROTONEMATA OF SPHAGNUM PAPILLOSUM LINDB., S. MAGELLANICUM BRID. AND S. CUSPIDATUM EHRH.
Authors: BOATMAN D. J. , LARK P. M.
Published: May 2006

Summary

The gametophores of Sphagnum spp. normally grow on peat and in oligotrophic waters, but attempts to grow the protonemata of S. papillosum, S. cuspidatum and S. magellanicum in natural waters failed. When the spores were sown on a cellophane disc in contact with a standard culture solution in special culture chambers however, protonemata consisting of a thallus with filaments developed from the spores of all three species. When the culture solution was diluted × 10, × 100 and × 1000, the size of the thalloid part of the protonemata became progressively less and the filamentous part was relatively more extensive. S. magellanicum failed to germinate when the solution was diluted × 100. The effect of reducing the concentration of each of the major ions individually was investigated and it was found that the thallus decreased in size as the concentration of phosphate was decreased. The protonemata failed to respond in a consistent way to nitrate and developed satisfactorily in the complete absence of the ion.

Natural waters were collected from five ombrotrophic mire sites in Scotland and the phosphate level raised to that of the 0.1 standard solution by adding sodium dihydrogen phosphate. In about half of the cultures (spread throughout the five waters) the form of the protonemata (S. papillosum only) was similar to that of protonemata in 0.1 standard cultures. When spores were immersed in culture solution, very small protonemata only developed.

It is concluded that protonemata of the species of Sphagnum used are unlikely to develop in mire pools because (a) the concentration of phosphate is too low and (b) the protonemata are unable to develop properly when completely immersed.
THE MECHANISM OF MYCELIAL STRAND INDUCTION IN SERPULA LACRIMANS: A POSSIBLE EFFECT OF NUTRIENT DISTRIBUTION
Authors: WATKINSON SARAH C.
Published: May 2006

Summary

Experiments were carried out on the conditions favouring strand formation in the mycelium of Serpula lacrimans. The mechanism of strand production proposed by Garrett and Butler (1960) was taken as a working hypothesis.

Colonies of the fungus were grown on a liquid medium of a nutrient composition found previously to induce stranding. In one set of cultures this medium was renewed daily by slow perfusion of fresh medium through the culture vessels, continued over a 6‐week period. In a parallel set of cultures the medium remained static and was not renewed over the same period. Strands formed only in these static cultures and not in the perfused ones. When the fungus was grown from a nutrient‐rich food base over media at a range of lower concentrations it was found that there was an optimal lower concentration for strand formation. Another state of nutrient supply that favoured the formation of strands occurred when mycelium growing out from a food base over a non‐nutrient medium encountered and began to colonize a fresh food base. This observation, first made on Helicobasidium purpureum by Valder (1958), was repeated using Serpula lacrimans and it was also shown by using 14C‐labelled glucose that carbon was transported between old and new food bases. Further experiments using 14C as a tracer showed that there was a loss of substances containing carbon from intact hyphae and from strand‐forming mycelium.

The significance of these results is discussed, and it is suggested that to Garrett's original hypothesis might be added the proposition that nutrient leakage from older hyphae is part of the process of strand induction.
SOME GENETIC FACTORS AFFECTING SEEDLING EMERGENCE IN RASPBERRIES
Authors: JENNINGS D. L.
Published: May 2006

Summary

The emergence of raspberry seedlings derived from two diallel crosses was studied, and also the effects on emergence of applying auxin to fruits 7 days after pollination. In one diallel, emergence was poor and the variations present were largely determined by maternal effects. In the other it was better and the largest variations were determined by inbreeding depression effects. In most cases maternal effects on emergence were negatively correlated with maternal effects on endosperm size, while inbreeding effects were associated with reductions in embryo size. Maternal interaction effects were of minor importance and were probably correlated with effects on the endocarp. The auxin treatments had variable consequences according to their effects on the seed tissues. It is concluded that the factors which determined seedling emergence would tend to maintain heterozygosity and should therefore be regarded as part of the breeding system.
DIPLOID‐TETRAPLOID SYMPATRY IN DACTYLIS(GRAMINEAE)
Authors: BORRILL MARTIN , LINDNER RUTH
Published: May 2006

Summary

The known zones of contact between diploid and tetraploid Dactylis are reviewed, and two well‐documented examples of intermixed and morphologically similar diploids and tetraploids are considered in detail. The relict subspecies mairei is accompanied, in its particular habitat, by a tetraploid counterpart. The evidence suggests this to be an example of autotetraploidy, the diploid and tetraploid components of which have been preserved by isolation in a specialized relict habitat.

In Dactylis interploid sympatry appears to have arisen in two ways–by changes in the original habitat, whereby morphologically dissimilar and spatially isolated diploids and tetraploids become intermixed, or by the formation of autotetraploids which co‐exist in the‘dipioid’habitat and may subsequently be modified by hybridization with other diploids or tetraploids with which they come in contact.

No triploid or tetraploid hybrids were discovered in the seedling progeny of dipioid Kerrata plants, hut the numbers screened are considered insufficient. Direct formation of tetraploid hybrids as a consequence of the functioning of unreduced gametes by dipioid parents can be a more effective‘genetic bridge’than the backcrossing of triploid hybrids. Further study of mixed diploid‐tetraploid stands is therefore required to determine the frequency and effectiveness of this phenomenon in natural populations.
CELL DIVISION IN CYANOPHORA PARADOXA
Authors: PICKETT‐HEAPS JEREMY
Published: May 2006

Summary

Mitosis in the nucleus of Cyanophora paradoxa is shown to be generally typical of other eukaryotic cells. Basal bodies and the flagella apparatus appear to replicate before nuclear division. At preprophase, microtubules approach the nucleus from the periphery of the cell to form the usual extranuclear spindle by prophase; at this stage the nucleolus begins its breakdown, which is soon complete. The spindle poles, clearly defined by the orientation of microtubules, never contained any obvious structural component, and basal bodies were never associated with the spindle. By prometaphase, breakdown of the nuclear envelope is accompanied by invasion of the nucleus by the extranuclear microtubules. During anaphase, two plates of chromosomes separate inside the spindle containing both continuous and chromosomal microtubules. Remnants of the nuclear envelope often coat the chromosomes. Cleavage, initiated by early anaphase, is achieved by an asymmetric, longitudinal constriction of the cell membrane, which passes between the replicated flagellar apparatuses. The plane of cleavage was always oriented at right angles to the spindle axis, and did not involve any detectable microfibrillar elements. Telophase nuclei reform as normal. These observations indicate that the host cell of the symbiotic pair cannot be considered as a dinoflagellate as had been previously suggested.

Division of the cyanelles is independent of nuclear division in the host, which therefore contains variable numbers of these symbionts. ‘Wall’ material is secreted into the furrow of the cleaving cyanelles. Furthermore, a very characteristic organelle was discovered in many cells invariably appressed to the cyanelles. Its dense granular contents were contained within a single unit membrane, and it was also frequently associated with endoplasmic reticulum. It was always inserted into the cleavage of dividing cyanelles and apparently it divided along with them, so that each daughter cyanelle remained associated with one of these inclusions. This organelle is thought to be a peroxisome and its possible significance in the host‐cyanelle relationship (and also in the evolution of chloroplasts) is briefly indicated.
THE CYTOKININS OF CULTURED SYCAMORE CELLS
Authors: MACKENZIE I. A. , STREET H. E.
Published: May 2006

Summary

Two cytokinin fractions, active in the tobacco and soybean callus bio‐assays, have been obtained from sycamore cells cultured in a cytokinin‐free medium. One of these (Cyt 1) corresponds in its properties to an uncharacterized cytokinin detected in water melon and cucumber seeds. The second fraction (Cyt 2) is coincident with zeatin riboside in chromatographic properties. No evidence was obtained for the presence of a ‘nicotinamide‐like’ cytokinin.

The ‘staled’ culture medium which had supported the growth of sycamore cells contained Cyt 1 activity, low Cyt 2 activity and a cytokinin coincident with zeatin in chromatographic mobility.

There is a rapid rise in the cytokinin activity in the cells during the lag phase which precedes active division in batch culture. Later the cytokinin activity per cell and per unit volume of culture progressively declines.
LEAF ABSCISSION IN COLEUS
Authors: HALLIDAY M. B. W. , WANGERMANN ELISABETH
Published: May 2006

Summary

The anatomical and histological development of the abscission zone is described in relation to the development of the whole leaf. The initiation of the abscission zone coincides with the change‐over from exponential to restricted growth in the blade. The response of explants from leaves at all stages of abscission zone development to a wide range of concentrations of indolyl acetic acid (IAA) applied at the distal end shows that concentrations of 10−9 M and lower accelerate, and higher concentrations retard abscission. Intact plants and excised abscission zones respond similarly. Delayed application of IAA to debladed petioles shows that it can reverse the abscission process for about 4 days after deblading. There is no evidence for an IAA‐accelerated phase in abscission. The effect of IAA is directly on the abscission zone.
DISAPPEARANCE OF NITRATE REDUCTASE ACTIVITY FROM CHLAMYDOMONAS REINHARDI
Authors: THACKER ANN , SYRETT P. J.
Published: May 2006

Nitrate reductase activity was induced in Chlamydomonas reinhardi following addition of nitrate. Enzymic activity was assayed in cell‐free supernatants and in whole cells whose permeability had been increased by freezing. Nitrate reductase activity in cells decreased rapidly when CO2‐fixation was prevented by (a) darkening cultures, (b) aerating cultures with CO2‐free air, or (c) addition of DCMU (3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea). A smaller loss of nitrate reductase activity from darkened cells occurred when (a) acetate‐adapted cells were supplied with acetate, or (b) cells were allowed to accumulate carbon reserves by nitrogen starvation before darkening. It was concluded that maintenance of nitrate reductase activity was dependent upon the availability of a suitable carbon source.
THE EFFECTS OF WATER STRESS ON NITROGEN‐FIXING ROOT NODULES
Authors: SPRENT JANET I.
Published: May 2006

Summary

The effects of osmotic stress on nitrogen fixation and respiration of soybean root nodules were investigated. Non‐electrolytes, such as mannitol, depressed acetylene reduction when given to detached nodules in sufficient concentration to withdraw water from them. When given to the root systems of whole plants, hypotonic concentrations of mannitol had a depressing effect after 1–2 hours, the exact time depending on the size of the nodules. Equivalent concentrations of salts had a much more rapid effect on whole root systems and on detached nodules (less than 5 minutes); 100 m‐equiv./l almost stopped acetylene reduction by small nodules. These effects could not be transmitted via the roots and needed contact between salt solution and nodules. They were accompanied by a decrease in respiratory activity and were fully reversible if the root systems were flushed with water within a few hours of treatment. High salt concentrations, as in sea water, had a rapid (1–2 minutes) effect, which after 20 minutes became irreversible.

The effects of salt stress are interpreted as resulting from alterations in the metabolism of the cortical cells of the nodules.
CARBOHYDRATE METABOLISM IN CHAETOMIUM GLOBOSUM
Authors: ADOMAKO D. , KAYE M. A. G. , LEWIS D. H.
Published: May 2006

Summary

Extracts of Chaetomium globosum contained an unstable, NAD‐dependent mannitol dehydrogenase, oxidizing mannitol to fructose. The enzyme had a low affinity for its substrates but showed high activity in vitro. Compared to fructose, exogenous mannitol was poorly utilized by the fungus. Raising the pH of the medium resulted in improved growth of the fungus on mannitol, in increased formation of ketose in the medium, and in stimulation of mannitol dehydrogenase formation. By contrast, glucokinase and fructokinase activities were depressed by growth at the higher pH.

The possible involvement of a mannitol dehydrogenase in the utilization of exogenous mannitol is discussed, together with the factors probably contributing to the poor growth of the fungus on mannitol and the control of cellular mannitol formation.
STUDIES IN FESTUCA
Authors: BORRILL MARTIN
Published: May 2006

Summary

The cytogeographic distribution and morphology of Festuca taxa in sections Bovinae and Scariosae has been compared with the results of experimental hybridization between them. Two groups have been established, the first is predominantly Moroccan and includes F. mairei (2n= 28), F. arundinacea varieties atlantigena forma pseudo‐mairei (2n= 56), letourneuxiana and cirtensis (2n= 70).

These taxa are closely related to the diploid F. scariosa endemic in the Spanish Sierra Nevada. Their distinctive morphological features are due to the inclusion of the scariosa genome. The second group, predominantly European, including F. arundinacea var. glaucescens (2n= 28) and F. arundinacea var. genuina (2n= 42), is similarly associated with the diploid F. pratensis. It is suggested that evolution in this species complex involved opportunities in a previous era for hybridization between tetraploid taxa now separated geographically. From such hybrids the higher polyploids can be derived.
THE TIME OF ORIGIN OF THE FLOWERING PLANTS DETERMINED BY USING AMINO ACID SEQUENCE DATA OF CYTOCHROME C
Authors: RAMSHAW J. A. M. , RICHARDSON D. L. , MEATYARD B. T. , BROWN R. H. , RICHARDSON M. , THOMPSON E. W. , BOULTER D.
Published: May 2006

Summary

Cytochrome c sequences from nineteen plants have been used, in conjunction with those of animal and fungal origin already published, to calculate the times of origin of the animal, fungal and plant kingdoms and also of some higher plant groups. The results show that the Angio‐sperms originated at least several geological periods before the Cretaceous, which is the earliest period in the geological record in which authentic angiosperm fossils have been found.
THE INTERACTION BETWEEN GROWTH PROMOTERS IN APICAL DOMINANCE
Authors: WOOLLEY D. J. , WAREING P. F.
Published: May 2006

Summary

Preliminary experiments with one‐node cuttings of Solanum andigena in sterile culture indicated that residual root effects, possibly due to stored cytokinins, could obscure the effects of exogenous growth promoters on lateral bud growth in rootless cuttings. Therefore two‐node cuttings, obtained from apical cuttings that had been maintained without roots for a number of days, were used in all subsequent investigations. Application of cytokinin or gibberellin to the base of rootless, two‐node cuttings promoted the growth of lateral buds as leafy, orthotropic shoots, or diageotropic stolons, respectively; simultaneous application of both hormones completely inhibited lateral bud growth. The effects of roots, 6‐benzylammopurine (BAP) and zeatin on lateral shoot growth were similar in leading to the formation of vigorous, orthotropic, leafy shoots.

Indole‐3‐acetic acid (IAA) completely inhibited lateral bud growth in rootless cuttings for at least 7 days, even when BAP was included in the nutrient medium. By using [α‐14C BAP it was demonstrated that cytokinin accumulates in the lateral buds of cuttings not treated with IAA, prior to their growth as leafy shoots; evidence of a causal relationship between cytokinin accumulation and lateral shoot growth was provided by a parallel experiment using [8‐14C]‐adenine. IAA did not appear to reduce BAP or BAP‐riboside accumulation in lateral buds by diverting these cytokinins to the point of IAA application, but did promote the formation of an unknown metabolite of BAP which accumulated in stem tissue.
CELL CYCLES IN A COMPLEX MERISTEM AFTER X‐IRRADIATION
Authors: CLOWES F. A. L.
Published: May 2006

Summary

Mean rates of mitosis, determined over short intervals of time by blocking the cell cycle at metaphase, fall immediately after X‐irradiation in most parts of the root meristem of Zea mays. The fall continues for several hours and is then replaced by a rise until normal rates are reached. In the quiescent centre, however, the mean mitotic cycle shortens to one‐third of its previous duration within an hour of irradiation. The rate of mitosis then falls to nearly its previous level before rising again at the same time as the acceleration of the cycle in the other regions. Finally quiescence sets in again as the other regions return to greater mitotic activity.

The observations suggest (1) that the reaction of the quiescent centre is not simply due to the relief of some inhibition imposed by the surrounding cells, (2) that something other than the different DNA levels of the various regions is in part responsible for the differential response, and (3) the resistance of the quiescent centre to irradiation is a real phenomenon requiring explanation.
ENDOGENOUS INORGANIC CARBON SOURCES IN PLANT HOTOSYNTHESIS
Authors: RAVEN J. A.
Published: May 2006

Summary

The quantity of CO2 arising from photorespiration in angiosperms and in algae has been estimated. Much of such CO2 arises from the metabolism of glycolate so that estimates are based on the rate of formation of glycolate and the rate at which it is metabolized (Table 1). The total CO2 production in leaves or algae in the light can then be taken as equal to the photorespiratory CO2 plus the CO2 produced by‘dark’ respiratory pathways.

Methods of estimating CO2 release from illuminated green tissues are considered and the rate of decarboxylation deduced from biochemical evidence of substrate turnover is compared with the observed rate of CO2 release; the difference between these values is reassimilation (Table 1). In angiosperms with the PGA pathway, in air, reassimilation is never complete and ranges from o to 0.6 of the endogenous CO2 production. This implies that the resistance to refixation is as great or greater than the resistance to loss of endogenous CO2 to the medium and is in accord with the relative values of these resistances based on other evidence. In law oxygen environment less glycolate is produced and hence less photorespiratory CO2; the resistance to refixation is smaller and so fractional reassimilation in increased. Unicellular algae have the PGA pathway and some appear to have more efficient reassimilation than the corresponding angiosperms.

The special problems of metabolism in four carbon acid plants are discussed. Such plants show essentially complete reassimilation since they do not lose CO2 when illuminated. In their leaves the resistance to escape of endogenously produced CO2 must be very much greater than the resistance to refixation. The low resistance to refixation is probably related to high levels of CO2 in chloroplasts which are generated by the‘CO2‐pump’ rather than to any peculiarities of carboxydismutase.

The importance of reassimilation is discussed in relation to the influence of CO2 on various aspects of metabolism, to isotopic discrimination in CO2 fixation and to the mechanism of the use of bicarbonate in photosynthesis.
THE EFFECT OF AUXIN FROM THE SHOOT ON ROOT DEVELOPMENT IN PISUM SATIVUM L.
Authors: McDAVID C. R. , SAGAR G. R. , MARSHALL C.
Published: May 2006

Summary

The effect of auxin of shoot origin on the growth and development of the root system of Pisum sativum L. cv. Kelvedon Wonder was investigated. Root growth was reduced when auxin transport from shoot to root was interrupted, but this could have been caused by a reduction in assimilate supply rather than a deficiency of auxin. Shoot removal, however, markedly reduced the number and total length of secondary roots produced and a 1% IAA–lanolin paste applied to the cut stump compensated to a large extent for shoot removal, markedly increasing secondary root growth in de‐shooted plants. It is suggested that auxin produced by the shoot may influence the growth and development of the root system.
REDUCTION OF ACETYLENE AND NITROGEN BY FIELD‐GROWN SOYBEANS
Authors: MAGUE T. H. , BURRIS R. H.
Published: May 2006

Summary

Acetylene reduction by soybean nodules started without a lag and remained linear with time for about 80 minutes. There was no apparent injury to nodules from evacuation. Rates of reduction of acetylene increased with increasing pO2 to 1 atm; respiration did not seriously deplete the available O2 from bottles in which nodules occupied less than 20% of the volume of the bottles. Reduction of acetylene decreased markedly in nodules soaked in water. About 0.2 atm acetylene supported the most rapid reduction of acetylene, and nodules 3–5 mm in diameter were most active. Intact soybean plants, nodulated roots and detached nodules fixed nitrogen at relative rates of approximately 100/46/23. The soybean plants exhibited a diurnal cycle of acetylene reduction dependent upon light intensity and air temperature. The observed ratio of acetylene reduced to N2 reduced was approximately 2.0 rather than the often assumed theoretical value of 3.0. There was a dramatic difference among soybean varieties in the date of onset and termination of acetylene reduction. Acetylene reduction was most vigorous in plants inoculated with a mixture of effective strains of Rhizobium japonicum.
EFFECT OF ENDOGONE MYCORRHIZA ON PLANT GROWTH
Authors: DAFT M. J. , NICOLSON T. H.
Published: May 2006

Summary

Endotrophic mycorrhiza in tomato and maize, induced by chlamydosporic varieties of Endogone macrocarpa, were examined quantitatively by estimating infection of roots, pigmentation of roots and production of ectocarpic chlamydospores. When the size of the root system was taken into account, estimates of infection showed a relationship to growth of the host. The amount of pigmentation within the root system gave a good indication of mycorrhizal intensity and was related to the size of the host at high levels of infection. The numbers of spores produced on an individual root system, given a particular treatment, were positively correlated with the size of the host. The relative merits of these different assessments of mycorrhiza are discussed.
THE RELATION OF RAY SPACING TO CAMBIAL GROWTH
Authors: CARMI A. , SACHS T. , FAHN A.
Published: May 2006

Summary

An experimental test was made of Bünning's (1965) hypothesis that the tangential spacing of the rays is determined by mutual inhibitory effects of the ray initials. Partial girdles of trunks of Ailanthus altissima were prepared in such a way that regions of the cambium were obtained in which cell division and differentiation occurred rapidly in the radial direction but not along the circumference of the trunk. Though the spacing of the original rays was not changed by this restricted growth, it was found that the rays grew in volume and many new rays were initiated. This result suggests that the rays differentiate along channels of a stimulus moving between the phloem and the differentiating xylem and their spacing is controlled not in the cambium but in the differentiating vascular tissues.
PLANT GROWTH RESPONSES TO VESICULAR‐ARBUSCULAR MYCORRHIZA III. INCREASED UPTAKE OF LABILE P FROM SOIL
Authors: HAYMAN D. S. , MOSSE B.
Published: May 2006

Summary

Onion plants were grown in a range of soils labeled with 32P. It was found that although the mycorrhizal plants had taken up more phosphorus and grown larger, the proportion of 32P to total P (specific activity) taken up by mycorrhizal and non‐mycorrhizal plants after 10 weeks was not significantly different. It is concluded that the mycorrhizal roots used the same source of labile phosphate but explored a greater volume of soil beyond the zone of phosphate depletion near the root surface. There was no indication that mycorrhizal roots had access to sources of phosphate different from those accessible to non‐mycorrhizal roots.

The specific activity of NaHCO3‐extractable phosphorus differed considerably between the eight soils but the specific activity of absorbed phosphorus in the plants always corresponded closely to that of the soil in which they had grown.
ENZYMIC DETERMINATION OF NITRATE BY USE OF FROZEN/THAWED CHLORELLA CELLS
Authors: HIPKIN C. R. , SYRETT P. J.
Published: May 2006

Frozen/thawed cells of Chlorella reduce nitrate quantitatively to nitrite which can be determined colorimetrically. 14–420 ng nitrate‐N can be determined. The method is suitable for the determination of nitrate in sea water.
RESPONSE OF ETIOPLASTS IN SITU AND IN ISOLATED SUSPENSIONS TO PRE‐ILLUMINATION WITH VARIOUS COMBINATIONS OF RED, FAR‐RED AND BLUE LIGHT
Authors: WELLBURN FLORENCE A. M. , WELLBURN A. R.
Published: May 2006

Summary

A quantitative comparison has been made of the ultrastructural development taking place in the light and in darkness between plastids in intact etiolated tissue and in suspensions of etioplasts, which have been given various pre‐treatments of red, far‐red and blue light. Plastid development in situ and in suspensions is enhanced by pre‐illumination with red light and this enhancement can be reversed by following red light with far‐red light. The reverse is also true; pre‐illumination with far‐red light inhibits development and this inhibition is abolished and replaced by enhancement by following far‐red light with red light. Blue light of short duration has no effect on the early stages of ultrastructural development in plastids.

It is concluded that a phytochrome‐mediated mechanism is present either inside the plastid or on the plastid envelopes.
UPTAKE OF PICLORAM BY EUCALYPT LEAF DISCS
Authors: SANDS R. , BACHELARD E. P.
Published: May 2006

Summary

Uptake of picloram by upper and lower surfaces of Eucalyptus viminalis juvenile leaves in light and dark, and measurements of stomatal resistances, were consistent with a major role of stomata in uptake.

Uptake of picloram and stomatal resistances of E. viminalis and E. polyanthemos leaf discs measured under varying experimental conditions also suggested a major role for stomata in uptake. This is discussed in terms of leaf surface characteristics and wettability.

Some premises on which arguments denying stomatal penetration of herbicides are based are examined, and concluded to be false.
THE ULTRASTRUCTURE OF LICHENS V. HYDROTHYRIA VENOSA, A FRESHWATER LICHEN
Authors: JACOBS J. B. , AHMADJIAN V.
Published: May 2006

Summary

The fine structure of the aquatic lichen Hydrothyria venosa was investigated from collections made in the summer and fall. The phycobiont lacked plastoglobuli in the summer but did contain them in the fall. Polyglucoside granules, structures not found previously in lichenized blue‐green algae, were present in the phycobiont. The mycobiont lacked ellipsoidal bodies, structures that have been found in almost all previously studied lichen fungi.
OBSERVATIONS ON THE SWOLLEN LATERAL ROOTS OF THE CYPERACEAE
Authors: DA VIES JAMES , BRIARTY LEWIS G. , RIELEY JOHN O.
Published: May 2006

Summary

A swollen and markedly hairy type of lateral root in the Cyperaceae is described which closely resembles the proteoid roots of certain Proteaceae. In both cases the existence of some biological causal agent outside the root tissue is indicated and the young swollen laterals of Carex flacca, examined with light and electron microscopy, exhibited no endophytes. These roots form extensive mats in the surface soil and the idea is advanced that they may play some particular role in the absorption of nutrients.
LONG‐RANGE TRANSMISSION OF TREE POLLEN TO SHETLAND
Authors: TYLDESLEY J. B.
Published: May 2006

Summary

Tree pollen was found in the air at Lerwick, Shetland in May and June 1970 and April and May 1971. The predominant species were birch and pine, and peak concentrations (daily mean) of 20 and 30 grains m‐3 respectively, were recorded. Trajectories on surface meteorological charts give good agreement of the catch with likely source areas in Scandinavia and Britain. Possible applications and extensions of the work are mentioned briefly.
THE UPTAKE OF METAL IONS BY LICHENS: A MODIFIED ION‐EXCHANGE PROCESS
Authors: PUCKETT K. J. , NIEBOER E. , GORZYNSKI M. J. , RICHARDSON D. H. S.
Published: May 2006

Heavy metal ions were absorbed by lichens to different degrees in laboratory experiments. The relative capacities for uptake from solutions containing a single metal ion were Fe, Cu>Ni>Pb>Co>Zn. Competitive uptake studies revealed the selectivity sequence Fe>Pb>Cu>Ni, Zn>Co. The sequences are in accord with a cation uptake mechanism involving ion exchange modified by metal‐complex formation. Correlations between laboratory studies and the metal content of lichens growing in the vicinity of a smelter are discussed.
THE DEVELOPMENT AND FINE STRUCTURE OF THE ASCUS APEX AND ITS ROLE DURING SPORE DISCHARGE IN XYLARIA LONGIPES
Authors: BECKETT A. , CRAWFORD R. M.
Published: May 2006

The development and structure of the ascus apex of Xylaria longipes were studied by light and electron microscopy. An apical body (Spitzenkörper) and vesicle system were associated with a localized thickening of the ascus wall to form an apical ring. On completion of the apical ring, the vesicles dispersed but the apical body remained, together with a dense ‘plug’ within the ring. Breakdown of the apical body and ‘plug’ was followed by the formation of fibrous material which linked the ascospores to the inside of the apical ring. Ascus dehiscence was accompanied by the complete eversion of the apical ring.