bluuebunny/crossref_metadata_2025_split huggingface dataset:
DESICCATION INJURY IN MOSSES
Authors: LEE J. A. , STEWART G. R. 
Published: May 2006

SummaryIntra‐specific differences in desiccation injury are shown in collections of Acrocladium cuspidatum, Climacium dendroides and Hypnum cupressiforme from habitats subjected to a wide range of moisture stresses. The degree of desiccation tolerance is correlated with degree of moisture stress in the habitat. Desiccation injury was measured as the decline in the initial rate of photosynthesis on remoistening. Collections of species from habitats in which severe moisture deficits occur show a slower decline in photosynthesis on desiccation and a more rapid recovery of function on wetting than collections from habitats with no appreciable moisture deficits. The results are discussed in terms of their ecological and physiological significance.
THE GROWTH OF PHLEUM ALPINUM L. IN CONTRASTING HABITATS AT A SUB‐ANTARCTIC STATION
Authors: CALLAGHAN T. V. , LEWIS M. C. 
Published: May 2006

SummaryThe effects of aerial microclimate and edaphic conditions on the growth of young vegetative tillers of Phleum alpinum L. from contrasting habitats on South Georgia have been investigated using growth analysis concepts. Relative growth rate (Rw) was found to be negatively correlated with habitat severity, there being a strong relationship between Rw and the amount of lateral production per tiller. Unit leaf rate (EA) was depressed at the highest altitude. Specific leaf area increased with habitat favourability but no simple relationship was apparent between leaf area ratio (FA) and site conditions. Native soils were shown to be severely limiting, although there was considerable variation in edaphic conditions between the various sites.There was striking uniformity in Rw values between plants from different populations when grown under similar conditions, this stabilization effect being produced by compensatory mechanisms involving the contributory growth parameters, EA and FA the specific leaf areas of the different populations when grown at one site were also very similar.
CYTOKININS AND THE GROWTH OF CULTURED SYCAMORE CELLS
Authors: MACKENZIE I. A. , KONAR APARNA , STREET H. E. 
Published: May 2006

SummaryExternally supplied cytokinins can induce cell division in sycamore cultures at cell densities at which, in the absence of a supply of cytokinin, they fail to grow. When cultures are initiated at cell densities where growth occurs in the absence of added cytokinins only after a long lag phase, the addition of cytokinins reduces the length of the lag phase. In these effects zeatin is fully effective at much lower concentrations than kinetin.As the duration of stationary phase is increased in the stock cultures, the ability of the cells to grow from a low initial cell density declines. This appears to be due to their declining endogenous cytokinin activity and declining ability to take up added cytokinin from their culture medium. It is postulated that, during the lag phase, the cells develop a critical level of cytokinin activity by an excess of endogenous synthesis over loss to the culture medium and internal degradation. When the phase of cell division has been initiated, the subsequent growth of the cultures is unaffected by low external levels of cytokinins.
STUDIES IN THE VEGETATIONAL HISTORY OF SCOTLAND
Authors: BIRKS HILARY H. 
Published: May 2006

SummaryLoch Maree, West Ross, is in an area of outstanding floristic and vegetational interest today. Native pinewoods occur on the south shore, and the largest northern oakwood on the north shore. High ground supports a range of montane communities.A pollen diagram is presented from the upper 460 cm of a 542 cm continuous core from Loch Maree. Six radiocarbon age determinations have been made from the sediments in relation to pollen stratigraphical changes. The constant sedimentation rate thus revealed has been used to interpolate ages for other events in the pollen diagram.During the last 9000 years of organic sedimentation in Loch Maree, many changes have occurred in the flora and vegetation of the landscape. After the instability at the end of the last glaciation, a climatic amelioration allowed juniper scrub colonization and organic soil development. Birchwoods, with some hazel, succeeded juniper, followed by the entry and rapid attainment of dominance by pine on all acidic soils, especially on the south shore of the loch, at about 8250 radiocarbon years ago. Meanwhile oakwoods with some ash and elm, developed in areas of more favourable soil and microclimate on the north shore. Alder immigrated and rapidly occupied all suitable habitats at about 6500 radiocarbon years B.P., and the pine forest began to degenerate. This process culminated in its rather rapid replacement by moorland and bog, perhaps due to climatic changes, at about 4200 radiocarbon years B.P. AS the oakwoods declined at the same time, human activity may have been an additional factor. However, there is little evidence for subsequent human interference in the area. The constant sedimentation rate suggests that deforestation was primarily by natural means, rather than by burning, felling, or grazing.Comparisons with pollen diagrams from other areas reveals an area of West Ross with a consistent Flandrian pollen stratigraphy. To the north and west, Betula and Corylus are the most important tree pollen types. In the eastern Highlands, Pinus pollen is again dominant, but the time of its expansion and the arrival of Alnus is different. The floristic composition of the pollen diagrams also differs, particularly in the abundance of pteridophytes.
AN APPLICATION OF FLUORESCENCE MICROSCOPY TO THE PROBLEM OF DERIVED POLLEN IN BRITISH PLEISTOCENE DEPOSITS
Authors: PHILLIPS LINDA 
Published: May 2006

SummaryThe fluorescence of fossil pollen and spores changes in colour and intensity with increasing age. By a study of Ipswichian Interglacial and Lower Pleistocene samples, it is shown that it is possible to distinguish Pleistocene from earlier pollen and spores by their different fluorescence colour and to a lesser extent by their different fluorescence intensity. The method can be employed in solving various problems of derivation in Pleistocene palynology.
PLANTS UNDER CLIMATIC STRESS
Authors: ROWLEY J. A. , TAYLOR A. O. 
Published: May 2006

SummaryThe composition of the atmosphere influenced the apparent photosynthetic rate of Sorghum bicolor and the degree of permanent damage to the photosynthetic capacity of the leaves when plants were transferred to low‐temperature, high‐light (10° C; 170 W m‐2) environmental stress. High CO2 (1000 μl/l) or low O2 (3%) both partially protect the plants compared to normal atmospheric levels, while low CO2 (30 μl/l) or O2 (50%) enhanced the damaging effects of stress. Oxygen levels are the more significant in control of permanent photosynthetic damage.
THE ROOTING OF ACTIVELY GROWING AND DORMANT LEAFY CUTTINGS IN RELATION TO ENDOGENOUS HORMONE LEVELS AND PHOTOPERIOD
Authors: SMITH N. G. , WAREING P. F. 
Published: May 2006

SummaryA series of poplar cuttings, Populus×robusta (Schneid.), excised at intervals during the summer showed a decline in rooting ability until mid‐August when cultured in long‐days. This was correlated with a decline in auxin at the RF of IAA. Leafy cuttings with growing apices rooted no better than dormant leafy cuttings when both were cultured in long days, and the bases of both types of cuttings possessed similar quantities of hormone at the RF of IAA.A bean hypocotyl bioassay of the ‘neutral’ ether fraction of an extract of terminal zones of poplar stems in August showed that the major root‐initiating hormone (RF 0.8 in 4:I, isopropanol: water) promoted no extension growth when assayed with wheat coleoptiles. Comparisons of the auxin levels at the base of July cuttings during the first 5 days after their excision showed an increase of auxin at the RF of IAA and of a neutral hormone near the solvent front.
A PHOTOELECTRIC DIGITAL SCANNER FOR MEASURING LEAF AREA
Authors: COX E. F. 
Published: May 2006

SummaryA scanning photoelectric method has been devised which is capable of measuring up to 680 cm2 of leaf tissue in 10 seconds. Its principle of operation is based on the number of dark pulses generated by a screw‐driven bank of photocells which is electronically scanned as it moves beneath an illuminated Perspex platform on which the leaves to be measured are arranged.
UTILIZATION OF SUGARS AND STARCH AS CARBON SOURCES IN THE ROOTING OF ETIOLATED STEM SEGMENTS OF POPULUS NIGRA
Authors: NANDA K. K. , JAIN M. K. 
Published: May 2006

SummaryStem segments of Populus nigra L. did not root in water or auxin alone but did so in 0.5% ribose, glucose and sucrose, sucrose being most effective. The addition of 0.1 mg/1 IAA or IBA to the medium stimulated rooting; IBA being more effective. Starch also induced rooting especially in combination with auxins. Starch was hydrolysed by enzymes that leached out of the segments and auxins enhanced their activity.
THE INHIBITION OF FUNCTIONAL RNA SYNTHESIS IN CHLORELLA PYRENOIDOSA BY 6‐METHYL PURINE
Authors: McCULLOUGH WILLIAM , JOHN PETER C. L. 
Published: May 2006

SummaryAddition of 10‐3 M 6‐methyl purine caused immediate inhibition of total RNA synthesis in Chlorella pyrenoidosa, 211‐8p, whereas inhibition of total protein synthesis developed progressively with time. 50% inhibition of adenine incorporated into RNA, and of de novo isocitrate lyase synthesis, was caused by 5 × 10‐5 M 6‐methyl purine, but a ten‐fold higher concentration was required to give a similar inhibition of total RNA synthesis. The inhibition of isocitrate lyase synthesis was reversed competitively by adenine. Isocitrate lyase synthesis was inhibited by 91% at a concentration of 10‐3 M 6‐methyl purine, which gave only 12% inhibition of glucose respiration. It is suggested that 6‐methyl purine acts by replacing adenine in RNA metabolism. It is concluded that 6‐methyl purine may be used as an inhibitor of functional RNA synthesis in Chlorella and that the synthesis of isocitrate lyase during the cell cycle is dependent upon concurrent transcription.
THE DISTRIBUTION OF ORGANIC FLUORINE IN SOME TOXIC TROPICAL PLANTS
Authors: HALL R. J. 
Published: May 2006

SummaryThe tissues of numerous species of toxic plants from Africa, Australia and South America have been analysed for organic and inorganic fluorine. The presence of organically combined fluorine was established in most of the species but was very variable in concentration. The stems and roots of the African Dichapetalaceae generally contained much more fluorine than did the leaves and the reversed situation was found in the same tissues of the Australian Gastrolobium and Oxylobium species and in the Brazilian Palicourea marcgravii. The seeds of most of the specimens analysed contained large amounts of organic fluorine but was absent in those of Acacia georginae. None of the plant species examined grew in soils which were high in fluorominerals; on the contrary some of the plants grew in soils containing exceptionally low levels of fluorine. A waxy exudate on the outside of the toxic leaves of A. georginae contained significant amounts of organic fluorine and is believed to be part of an excretory mechanism. Only a small proportion of the exudate was identified as fluoroacetate and there appear to be other fluorinated organic compounds present. A crystal formation which contains fluorine was observed in the bark of the roots and stems of Dichapetalaceae and is thought to be also associated with a detoxication process. The crystals appear to be a complex mixture containing calcium oxalate, chloride, fluorine, magnesium and silica. The analytical findings suggest that in the plants in which carbon‐fluorine compounds have been established, the site of the synthesis of organic fluorine may vary with the species and that metabolism to inorganic fluoride may take place continuously and simultaneously with the organic bio‐synthesis.
VESICULAR‐ARBUSCULAR MYCORRHIZAS OF THE SPECIES OF A MOLINIETUM COERULEAE L.I. ASSOCIATION: THE ECOLOGY
Authors: MEJSTRIK V. K. 
Published: May 2006

SummaryThe frequency and intensity of vesicular‐arbuscular mycorrhizas in the species of a Molinietum coeruleae association was studied during the vegetative period. From the total number of fifty‐five species in the association only nine species were nonmycorrhizal. There was dependence of the frequency of entry points on the root depth and the vegetative season. The ground water table was relatively stable during the year and it did not exert strong direct influence on the intensity of mycorrhizal infection.
PRELIMINARY OBSERVATIONS ON THE ULTRASTRUCTURE OF MATURING CORK‐CELLS FROM TUBERS OF SOLANUM TUBEROSUM L.
Authors: RAINBOW ARNOLD , WHITE D. J. B. 
Published: May 2006

SummaryThe normal cork of young tubers of Solanum tuberosum L. cv.‘King Edward’ was used as a source of maturing cork‐cells. The cells are periclinally flattened and highly vacuolated. Electron‐micrographs reveal that the cytoplasm, although sparse, is rich in mitochondria, ribosomes and membrane‐bound vesicles. Electron‐opaque crystals and endoplasmic reticulura are also present, but neither the plasmalemma, nor the tonoplast, are visible. Microtubules are seen at the interface between the cell wall and the cytoplasm. The layered appearance of the cell wall is compatible with the observations of other workers. No pits are visible but there is evidence that plasmadesmata were present earlier in the ontogeny of the cell. The significance of these observations is discussed in the light of existing information on cork‐cell differentiation.
SAMPLING SYSTEMS TO ASSESS VARIABILITY IN THE NEEDLES OF TWELVE MEXICAN PINES
Authors: WOOD P. J. 
Published: May 2006

SummaryThe needle characteristics were studied of twelve Central American and Caribbean pines planted in a 3‐year‐old trial at Chati, Zambia, using a multistage sampling system with four levels. Variation patterns are given graphically for seven traits for each species, showing the effects of varying the sampling intensity at different levels. The practical aspects of the patterns found are discussed.
STUDIES IN THE VEGETATIONAL HISTORY OF MID‐WALES
Authors: MOORE P. D. 
Published: May 2006

SummaryPollen analysis has been conducted upon a mire site at an altitude of 312 m on the Mynydd Bach region of western Cardiganshire. The sediments subjected to analysis began forming at the close of the post‐Allerød cold phase (zone III sensu Godwin) and document vegetational history in the area up to the time of the elm decline, after which deposits appear to have suffered interference by peat cutting.A number of the features present at this westerly site are of particular interest, especially the early rise of Corylus in the Flandrian. Corylus pollen (expressed as % arboreal pollen) began to rise at this site before the zone III/IV Juniperus peak. As one moves progressively north in western Britain, so the Corylus rise is delayed until well after the juniper peak. This time lag is considered to reflect the migration rate of Corylus as well as offering an opportunity to trace its route up the western edge of Britain, gradually extending eastwards and into regions of higher altitude.Pine values are low at Gwarllyn throughout the early Flandrian, in contrast to the upland areas of Cardiganshire, where pine increases to a maximum in zone VIc, It is postulated that Pinus was less successful in the western lowlands as a consequence of the greater competitive ability of Quercus under the prevailing climatic and edaphic conditions in those regions.
NUMERICAL METHODS IN QUATERNARY PALAEOECOLOGY I. ZONATION OF POLLEN DIAGRAMS
Authors: GORDON A. D. , BIRKS H. J. B. 
Published: May 2006

SummaryThe concept of the pollen zone as a fossil assemblage zone is discussed, and the advantages of numerical approaches to the recognition and delimitation of such zones are considered. Existing procedures are reviewed, and original constrained agglomerative and divisive procedures are advanced. The results of these procedures are discussed in relation to existing zonation schemes for three sets of data, and the limitations and potentialities of the procedures are considered. The initial zonations suggested by visual inspection are, in general, confirmed by the numerical procedures. The application of these procedures to the subdivision of both pollen and macro‐fossil data in the same stratigraphical sequence is also discussed. Details are given of the computer time and storage required for the analyses.
A SIMPLE METHOD OF ISOLATING STOMATA ON DETACHED EPIDERMIS BY LOW pH TREATMENT: OBSERVATIONS OF THE IMPORTANCE OF THE SUBSIDIARY CELLS
Authors: SQUIRE G. R. , MANSFIELD T. A. 
Published: May 2006

SummaryMost previous studies of stomatal behaviour on isolated epidermis of Commelina communis have been carried out in media of pH 6.5‐7.0. In the present investigation we have used a wide range of pH values obtained with several different buffers, and have paid special attention to the response of the epidermis to incubation in media of pH 4.0‐5.0. Within this region of pH, all the cells of the epidermis apart from the guard cells were severely damaged, a condition leading to considerably enhanced stomatal openings even in media containing low concentrations (1 mM) or completely lacking inorganic cations. The guard cells appeared to continue to function normally, with stomatal apertures changing in response to light and CO2, and the cells showing the expected solute potential changes and potassium accumulation as opening occurred. The stimulation of opening might, in part, be attributable to the removal of pressure from the surrounding cells.Exposure of epidermis to a pH of 4.5 for 1 1/2 hours proved to be a highly effective method of destroying all the cells apart from the guard cells, which apparently remained fully functional. This is a quick and reliable way of‘isolating’ stomata which could prove invaluable in future studies of their physiology and metabolism. A comparison of stomatal responses to solutes in the medium for epidermis with all cells intact and for epidermis with isolated stomata suggests a role for the subsidiary cells in regulating solute entry into the guard cells.
LIFESPAN AND BUDDING POTENTIAL OF LEMNA AS A FUNCTION OF AGE OF THE PARENT– A GENEALOGIC STUDY
Authors: CLAUS WALTER D. 
Published: May 2006

SummaryExperiments tested claims that, in Lemna, increasing age of the parent reduces lifespan and reproductivity of the offspring. Successive cultures of nth buds (‘nth‐bud lines’, n= 1–10), and also of late‐buds and last‐buds, were observed for size and number of the buds they produced, and lifespan. Advancing age of the parent frond affected bud size, but had little or no effect on either lifespan or budding capacity of the offspring. First, second, and third buds of all lines were larger than their parents; successive buds then decreased in size approximately linearly with bud number or time of separation. Small, late buds, as parents, have smaller buds than do their early siblings. Numbers of buds produced by late buds, as parents, differ little from the numbers produced by their earlier siblings. Both groups vary randomly; together, their productivity is well represented by a normal distribution curve. Lifespans of early and late buds do not, on the average, differ markedly. ‘Survival curves’ indicate that early buds are more likely to survive into middle age (to produce nine‐ten buds), but late buds are more likely to survive into very old age and to produce thirteen‐fifteen buds. Bud production by late offspring is somewhat slower than that by early offspring.
ELECTROPHORETIC CHARACTERIZATION OF EUCALYPT MYCORRHIZAS
Authors: SEVIOUR R. J. , CHILVERS G. A. 
Published: May 2006

SummaryDisc electrophoresis of extracts from mycorrhizas synthesized with different eucalypts, produces similar protein patterns when the same fungal symbiont is involved. Consequently, where sufficiently large homogeneous clusters of mycorrhizas can be collected, the technique is a valuable adjunct to anatomical classification of naturally occurring mycorrhizas.
BREEDING SYSTEMS IN COTULA L. (COMPOSITAE, ANTHEMIDEAE)
Authors: LLOYD DAVID G. 
Published: May 2006

SummaryFive classes of sex expression are distinguished in Cotula on the basis of the degree of separation of male and female gametes on different flowers and plants. These classes are divided into sexually monomorphic and dimorphic systems. The order–monocliny, gynomonoecy, monoecy, subdioecy, dioecy–places the five classes in a linear sequence of increasing dependence for fertilization on the transfer of pollen between flowers and plants. Four of the five major taxonomic groups in Cotula and five species have more than one class of sex expression. The four monoecious and gynomonoecious species tested are self‐compatible. The morphology of hermaphrodite, male and female florets are compared.Seven additional characters are associated with sex expression in New Zealand species. In general, the extent of protogyny, brightness of flowers, degree of retraction of stigmas and anthers, floret length, head diameter, peduncle length and the number of pollen grains increase from gynomonoecious through monoecious to dimorphic (dioecious or subdioecious) populations. But within each kind of sex expression there is considerable variation in these ancillary characters. A MAS (measurements associated with sex expression) index is calculated from the four quantitative characters for each New Zealand species (or part‐species where there are two kinds of sex expression in a species). The MAS index reflects the expenditure of energy on adaptations to cross‐pollination and provides an approximate measure of the relative frequency of outbreeding. The MAS indices of the species and part‐species indicate a continuous array in the expression of adaptations to cross‐pollination and the frequency of outbreeding. The different kinds of sex expression occupy characteristic but overlapping segments of this array and ought to be considered as convenient classes which only specify the breeding system approximately.
VARIATION IN GENTIAN A VERNA L.
Authors: ELKINGTON T. T. 
Published: May 2006

SummaryThe British populations of Gentiana verna are clearly distinguishable morphologically into two groups by both calyx and leaf characters. These groups are coincident with the geographical areas of the species, Teesdale in north England and Galway Bay in west Ireland. On the Continent, populations from the Alps and Pyrénées are indistinguishable in calyx characters, but are significantly different from English and Irish populations. Leaf length and length/ breadth ratio are correlated and the leaf length/breadth ratio of the Continental populations is clinally correlated with their altitude. Leaf characters of British populations are similar to those Continental populations from higher altitudes, those from Teesdale being indistinguishable from those at the highest altitudes. It is considered that these differences may either be the result of random drift or genecological differentiation. The possibility of variation in leaf morphology being related to heat transfer properties is discussed.
POSSIBLE PHANTOM HYBRIDS IN EUCALYPTUS
Authors: PARSONS R. F. , KIRKPATRICK J. B. 
Published: May 2006

SummaryThe distribution of Eucaiyptus cypellocarpa, E. goniocalyx and four populations apparently morphologically intermediate between these two but isolated from them is described in an area near Melbourne, Victoria. Scatter diagrams of various characters from both mature trees and progeny document and confirm that the four populations are intermediate. However, the variability of their progeny is not markedly different from that of the‘pure’ species and is not as high as that of recent hybrids between the two species. It is suggested that the four populations represent either old hybrid swarms now stabilized by selection from which the parents have disappeared, or that they arose without hybridization (a) by selection from a single species or (b) as a former cline between both species. The difficulties in interpreting the origins of such stands are pointed out.