bluuebunny/crossref_metadata_2025_split huggingface dataset:
CHEMISTRY OF THE PLANT VIRUSES
Authors: McFARLANE A. S. 
Published: January 2008

Summary1. By fractional precipitation of the crude sap from virus‐infected plants, or by ultracentrifugation, protein substances are obtained which are capable of transmitting the disease. These proteins may be purified by various methods, notably by incubation with trypsin which selectively digests the impurities. They have high phosphorus contents and behave as nucleoproteins.2. Examination in the ultracentrifuge reveals that these proteins have larger molecules than any hitherto discovered. In carefully prepared specimens the sedimentation boundaries are those of perfectly homogeneous substances. Sedimentation constants varying from 115times10–13 to 240times10–13 have been obtained for different viruses.3. The viruses are stable inside the range pH 2.0–9.0, although showing often an insolubility zone. They are electrochemically homogeneous inside the stability range with isoelectric points somewhere between pH 3 and 5.4. One virus, that causing Bushy stunt disease, has a spherical molecule and gives regular crystals. The others are anisotropic and give ill‐defined needles. Purified solutions of the anisotropic viruses show marked birefringence of flow, and this phenomenon in conjunction with X‐ray analysis has been used to obtain estimates of the molecular parameters. In the case of the tobacco mosaic virus the thicknzss of the molecule is 15 mμ. and the length probably 40 times this value. Bushy stunt virus has a diameter of 27 mμ. and a molecular weight of 8,800,000.5. The crystallinity of the viruses cannot be regarded as a proof of their purity. X‐ray measurements on the crystals show that these have the intramolecular pattern characteristic of proteins. Measurements on semi‐dry films of virus show that in these the molecular rds are closely packed together with very little space for water or any foreign substance between them.
THE PRIME VARIABLES OF MEIOSIS
Authors: DARLINGTON C. D. 
Published: January 2008

Summary1. The uniform series of chromosome movements we know as meiosis (pairing, torsion, reproduction, crossing‐over, co‐orientation, segregation) can now be placed in a causal sequence. This serves two purposes: to be tested as a working hypothesis and to be applied to the understanding of the characteristic variations of which meiosis is susceptible.2. Comparison of mutants, hybrids and other genetically controlled variants shows that these variations arise from three main sources: (i) the point at which the pairing chromosomes make contact; (ii) the time available for pairing; (iii) the amount of torsion capable of being developed in the parts of the chromosomes which are paired.3. All species are, as such, characteristically co‐ordinated with regard to these variables. They may be classified as procentric (Mecostethus) or proterminal (Chry‐sochruon) in the initiation of pairing. This difference affects the relative frequency of crossing‐over in chromosomes of two main types, with the centromere near an end and away from it (Fritillariu, Lilium).4. Exceptional cells, and individuals arising by segregation from hybrids, show that co‐ordination within the cell and the individual is not physiologically inherent in meiosis. Unco‐ordinated behaviour can take place in regard to all three prime variables (Allium, Lilium and Trillium).5. The time limit to pairing may be imposed artificially by heat treatment or X‐raying. We then have artificial localization of crossing‐over (Uvularia, Vicia).6. The amount of torsion depends on the speed of pairing and this in turn on the size of the nucleus. Doubling the chromosome number therefore reduces the crossing‐over frequency (Primula, Allium, Solanum, etc.).7. The preservation of torsion depends on the early contact of a chromosome at two points. The more numerous contact points of triploids therefore increase their frequency of crossing‐over per unit length paired, at the same time changing its distribution (Fritillaria, Tulipa, Drosophila).8. All species hybrids are structural hybrids. Their pairing is therefore slower and is cut short by the time limit. Hence their crossing‐over is reduced and relatively localized, unless the extreme of localization has already been reached in the parents (Triticum, Lilium).9. The study of the three prime variables is therefore necessary for the understanding of the causal sequence of meiosis and of the conditions of stability and coherence in species.
CELLULAR INHERITANCE AND TRANSFORMATION
Authors: MEDAWAR P. B. 
Published: January 2008

Summary1. The article summarizes the empirical evidence relating to the production of inherited character differences between cells that generate cell lineages by asexual fission.2. The modes of cellular transformation are classified under three headings: adaptive transformations, including antibody formation and some forms of bacterial adaptation; infective transformations, including those secured by viruses, some cellular transformations of micro‐organisms, and a colour transformation of mammalian skin; and inductive transformations, mainly exemplified by carcinogenesis and embryonic evocation.3. Selective transformations of populations of cells are considered only as they may qualify the interpretation of the other types.4. Adaptive transformations are defined as initially reversible and progressively induced particulate changes in cellular heredity that are functionally dependent in degree and kind upon the nature of the transforming stimulus.5. Infective transformations are defined as heritable and serially propagable cellular transformations, not normally reversible and not progressively induced, in which the continued presence of the transforming agent or a replica of it is a necessary condition for the maintenance of the transformed state.6. Inductive transformations are defined as heritable cellular transformations, normally irreversible, not serially propagable, and not progressively induced, in which the maintenance of the transformed state after its initiation does not depend on the continued presence of the inductive stimulus.7. The inherited character differences between cells are particulate and combinatorial in nature, and there is ground for supposing that they are mediated by cytoplasmic entities that behave as discrete self‐reproducing particles.
SOIL MOISTURE AND THE ECOLOGY OF SOIL FUNGI
Authors: GRIFFIN D. M. 
Published: January 2008

SummarySome basic concepts concerning soil physical factors have been briefly discussed. The importance of evaluation of the total soil moisture stress, as indicative of the energy which must be used by an organism to gain water from the soil, is shown. This total stress can be divided into tensiometric and osmotic components, of which the latter is important only in saline or heavily fertilized soils and is but briefly mentioned. Tensiometric suction is discussed and shown to be best described along with a measure of the texture and structure of the soil by means of the moisture characteristic. From such a characteristic, additional information concerning porosity and aeration can be obtained.Although there are few published experiments in which suction has been measured, none suggests a limitation of fungal growth directly due to suction factors in the soils between saturation and the permanent wilting point of mesophytic higher plants. Evidence derived from controlled humidity experiments reveals that most fungi can exert sufficient force to absorb water from atmospheres at a lower relative humidity than those in equilibrium with soil at the permanent wilting point. It is then suggested that absorption of soil water per unit area of absorptive surface will need to occur much less rapidly in the case of soil fungi than of higher plants, so that the growth of the former will not be limited to the same extent by reduction in the hydraulic conductivity of the soil. The conclusion is drawn that the majority of fungi will probably be able to grow in soils somewhat, or even considerably, drier than the permanent wilting point of higher plants.From an examination of the evidence it is concluded that in a compact soil spores are dispersed by the soil water only when that water is moving through a nearly saturated soil. In natural soils, however, where cracks, root channels, etc., are present, rapid movement of water, and thus of spores, may take place to a considerable depth even when the general soil mass is far from saturated.The literature reveals that such factors as moisture content, texture and structure, which affect soil aeration, have a profound influence on fungal activity and it is postulated that aeration is, in fact, the effective agent. Although the evidence is far from adequate, it appears that both excess of carbon dioxide and an insufficiency of oxygen are implicated as inhibitors.I wish to pay particular tribute to Professor N. Collis‐George who provided the initial stimulus for me to begin investigations in the field which forms the topic of this article and who has been of much assistance to me in discussion. I also wish to thank Dr E. C. Childs and Dr S. D. Garrett for discussion and for reading and criticizing various sections of the manuscript and to thank Dr D. J. Greenwood for advice concerning soil aeration. I am grateful to Professor H. Godwin for providing accommodation for me at the Botany School, Cambridge, for a period during which this article was written.
THE EVOLUTION OF THE OVULE
Authors: SMITH DAVID L. 
Published: January 2008

Summary1. After reviewing current theories on the origin of the pteridosperm ovule it is concluded that only one, the telomic concept, can account for all the structural variations found within the group.2. It is therefore suggested that in at least most cases the pteridosperm ovule evolved by the enclosure of a terminal sporangium within an integument derived from a number of adjacent branches or telomes.3. A cupule or second integument, often enclosing more than one ovule, later evolved by a similar process.4. The available evidence suggests that both integument and cupule evolved independently a number of times and that consequently the ovule itself must have arisen several times in the pteridosperms.5. Since the possession of an ovule is the one important feature common to the whole group, this implies that the pteridosperms must have had a polyphyletic origin.6. It is suggested that Cordaitalean ovules are primarily radially symmetrical, having a first integument derived from several telomes, and that they became bilaterally symmetrical with the evolution of a second integument derived from only two telomes.7. Evidence provided by the ovule supports the view that the Cordaitales are monophyletic.8. There is no foundation for the view that the ovulate organs of the Cordaitales are stachyosporous. The same is probably true of the pteridosperms.9. Evidence of a direct relationship between the pteridosperms and the Cordaitales is inconclusive.
FINE STRUCTURE OF FUNGI AS REVEALED BY ELECTRON MICROSCOPY
Authors: HAWKER LILIAN E. 
Published: January 2008

Summary1. The cells of yeasts and filamentous fungi are surrounded by a cell wall. The cytoplast is bounded by a plasmalemma and contains nuclei, mitochondria, food granules and vacuoles.2. Cell walls of vegetative fungal cells usually possess a microfibrillar ‘skeleton’, architecturally similar to that of plants, but composed of chitin or hemicellulose. True cellulose predominates only in the Oomycetes. Spore walls are often differently constructed from those of vegetative cells of the same species.3. The cell contents (plasmalemma, endoplasm and endoplasmic reticulum, nucleus, mitochondria, vacuoles and miscellaneous granular inclusions), as seen in sections and in centrifuged material, are in general similar to those of plants. Some minor differences are indicated. The structure of the flagella of motile cells of the Lower Fungi is fundamentally similar to that of the flagella of lower plants and animals.4. The electron microscope has contributed to our knowledge of growth and development of fungal structures. It has extended previous knowledge of the process of budding in yeasts, of the development of haustoria and of the formation and germination of fungal spores.5. Poor nutrition, anaerobic conditions and sublethal irradiation cause abnormalities in the structure of mitochondria. Toxic amounts of irradiation prevent normal nuclear division in budding yeast cells.6. Electron microscope studies have aided taxonomy by demonstrating fundamental structural differences between Fungi and Actinomycetes and between certain subdivisions of the fungi.
CALCIUM AND PLANT GROWTH
Authors: BURSTROM H. G. 
Published: January 2008

SummaryCalcium as a plant nutrient is characterized by its relatively high content in the plant coupled with a requirement not much higher than that of a micro nutrient element and an exceedingly uneven occurrence in soils. The difficulties in defining its actions are accentuated by a weak biochemical activity. In ecological conditions the secondary consequences of variations in calcium content may be more striking than the direct ones.Electron‐microscopical studies have revealed that calcium is required for formation and maintenance of lamellary systems in cell organellae, a fact which might suffice to explain its indispensability for meristematic growth.Calcium is required for cell elongation in both shoots and roots; the common experience that it inhibits shoot elongation is certainly due to calcium additions far above actual requirement.It must be assumed for a rational interpretation of cell elongation that the fundamental mechanism is the same in shoots and roots. The one action which can be ascribed with certainty to calcium is a stabilizing of the cell wall with an increase in rigidity, an effect which, with over‐optimal supply, may lead to growth inhibitions. The function is, however, necessary for the normal organization of cell walls. Calcium has, on the contrary, no significant effect on the synthesis of cell wall compounds but appears to act on their proper incorporation into the cell wall.The growth‐active calcium may be bound not only to pectins but also to proteins and nucleoproteids in or in close contact with the cell wall.The supposition that calcium interacts directly with auxin in the cell wall has not been verified and does not seem very probable. There are reasons to believe that the points of action of calcium and auxin in the cell wall differ, auxin inducing growth by wall loosening and calcium establishing new wall parts.For submerged organs it may be necessary to consider an indirect effect of calcium on growth by its regulation of cytoplasmic permeability and thus affecting the exudation of growth‐active compounds.The ecological problem is to characterize calcifuges (acid soil plants) from calcicoles (base soil or calcareous soil plants). Growth inhibitions on acid soils depend upon poisoning by A13+ and Mn2+. Opinions differ as to what extent this can be antagonized by calcium. Lime‐induced chlorosis in calcifuges depends upon iron deficiency or iron inactivation in the plant. No acceptable explanation is given, but it might be related to an interaction of calcium carbonate, phosphorus, and iron. A hypothesis that it is linked to formation of organic acids is not tenable in the given form.Plants react to the calcium ions in the concentrations found in soils. Calcifuges have a low calcium‐optimum for growth and show growth inhibition at high concentrations. Calcicoles have a high optimum for growth. Calcifuges are resistant to aluminium poisoning. Attempts made to explain the differences in calcium uptake and generally in salt uptake are tentative only, and relevant data are lacking.
MEMBRANOUS STRUCTURES IN YEASTS
Authors: MARCHANT R. , SMITH D. G. 
Published: January 2008

Summary1. Most yeast cells carrying out active respiration have spherical or ellipsoidal mitochondria, with plate‐like cristae.2. Cytoplasmic petite strains of Saccharomyces cerevisiae have aberrant mitochondria, often containing whorled membranes. Mutants with deficiencies in the tricarboxylic acid cycle have mitochondria which appear normal when the cells are grown in low levels of glucose.3. Cells of normal and petite S. cerevisiae grown strictly anaerobically show no recognizable mitochondrial profiles.4. Carbon substrates which can only be respired promote the development of well‐defined mitochondria. In certain facultatively anaerobic yeasts respiration is suppressed by glucose and the mitochondria under these conditions are large, pleomorphic and few in number. Other fermentable carbohydrates do not give this repression.5. A number of antibacterial antibiotics, which inhibit mitochondrial protein synthesis, cause a disorganization of the mitochondrial cristae.6. In yeast cells adapting from anaerobic to aerobic conditions mitochondria appear to develop from proliferations of the endoplasmic reticulum, which become progressively more organized.7. Vacuoles often contain granular material, but in S. cerevisiae the vacuole, which has been described as a lysosome, frequently contains myelin‐like lipid inclusions. The material in these inclusions is apparently derived from spherosomes.8. Endoplasmic reticulum, orientated parallel to the plasmalemma, may be associated with fermentative ability in certain facultatively anaerobic yeasts. Endoplasmic reticulum is also actively involved in the budding process.9. Normally the yeast‐cell plasmalemma shows only minor convolutions, but in chloramphenicol‐grown Rhodotorula glutinis the plasmalemma produces vesicular structures termed ‘paramural bodies’.10. The yeast nuclear membrane has about 200 pores occupying 6–8 % of the total surface area. The nuclear membrane remains intact during mitotic division in yeasts until the daughter nuclei separate.
FOSSIL BRYOPHYTES
Authors: LACEY WILLIAM S. 
Published: January 2008

Summary1. The rapid increase in the knowledge of the early geological history of bryophytes which has taken place in recent years is emphasized.2. An explanation for this unexpected development is sought in a consideration of the conditions necessary for the preservation of bryophytes as fossils.3. It is concluded that the chances of preservation depend not so much on the conditions suitable for the growth of bryophytes or the possession of resistant structures (although both can be important contributory factors) but on the occurrence of the right kind of sedimentation in the right place at the right time.4. The fossil history of the main Orders of the Bryophyta is then systematically reviewed, with special reference to first records in the Palaeozoic and Mesozoic.5. A number of problematic bryophyte‐like fossils of Palaeozoic age are also reviewed. Four (Protosalvtnia Dawson, Sporogonites Halle, Tetrapterites Sullivan and Hibbert, and a Dicranum‐like plant from South Africa) are accepted as probably bryophytic; three (Musciphyton Greguss, Hepaticaephyton Greguss, and an alleged bryalean sporogonium from the Rhynie Chert) are rejected on the grounds of insufficient evidence.6. The bearing of the fossil evidence on bryophyte evolution is briefly considered.7. It is shown that the principal groups of both liverworts and mosses had already been differentiated before the end of the Palaeozoic.8. A polyphyletic origin of the Bryophyta is therefore highly probable.9. Beyond this, the early fossil evidence as yet gives no unequivocal answers and more detailed phylogenetic speculation based on the present state of knowledge of fossil bryophytes has little value.10. Further knowledge of the early fossil history of bryophytes is needed and it is suggested that this is most likely to be obtained by patient systematic search in finegrained freshwater sediments by bulk maceration techniques.
THE CONTROL OF HAEMOGLOBIN SYNTHESIS
Authors: MACLEAN NORMAN , JURD RICHARD D. 
Published: January 2008

Summary1. Haem and globin are synthesized separately by living cells before their conjugation to form haemoglobin.2. Protohaem is the form of haem utilized in the structure of haemoglobin, myo‐globin, erythrocruorin, catalases, some peroxidases and cytochromes of class B. All cells capable of aerobic respiration have the potential ability to synthesize haem.3. The main control mechanism in haem production is exercised by the enzyme ALA synthetase, and by cellular control over the level of activity of this enzyme.4. Haem probably affects the rate of globin synthesis but an effect of globin on haem synthesis is uncertain.5. Many organisms synthesize a variety of globins, some apparently exclusive to particular developmental stages. We suggest that the multiplicity of types of globin, whether changing during development, or present in balanced proportions in the adult, are not the result of evolutionary selection but of non‐adaptive changes in multiple copies of the primitive globin cistron.6. Ontogenic changes in the type of globin synthesized seem to be effected by differing mechanisms in different organisms. In some animals the changes seem to occur within one line of cells, whereas in others there is evidence for replacement of one cell population by another as in the switch from the embryonic to the adult or from tadpole to adult form of haemoglobin.7. Both transcriptional and post‐transcriptional control mechanisms are involved in globin synthesis, but the effects of the cell cycle and cell division on such regulation deserve intensive study in eukaryotic systems. We suggest that studies of globin synthesis provide evidence favouring some form of ‘linear reading’ of the genetic message.8. The hormones thyroxine and erythropoietin both affect haemoglobin synthesis in at least some organisms, and there are similarities in the pattern of action of the two hormones on erythropoietic tissues.9. All classes of RNA must affect globin synthesis and the isolation of globin mRNA has provided a particularly useful biochemical tool.10. Haemoglobin synthesis in artificial heterokaryons is of considerable interest but still poorly understood.11. The final assembly of tetrameric haemoglobin involves the conjugation of free haem with αβ globin dimers, the β globin chains apparently remain bound to ribo‐somes until they join with an α globin from the cellular pool of α globin. The mixed tetramer which is the most common form of haemoglobin possesses functional advantages over tetramers of only one globin type.