bluuebunny/crossref_metadata_2025 huggingface dataset:
FINE STRUCTURE OF FUNGI AS REVEALED BY ELECTRON MICROSCOPY
Authors: HAWKER LILIAN E.
Published: January 2008

1. 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

Calcium 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

1. 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

1. 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

1. 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.
THE SIGNIFICANCE OF IONIC CONCENTRATIONS IN THE INTERNAL MEDIA OF ANIMALS
Authors: BURTON RICHARD F.
Published: January 2008

1. The electrical and ionic gradients across a cell membrane depend on its permeability properties, on the concentration and net valency of the organic constituents of the cytoplasm and on the critical energy barrier to the extrusion of sodium. Such considerations do not, however, explain the small extent to which the concentration of potassium varies in myoplasm which may, instead, be related to the effects of potassium on particular enzymes.

2. The fact that the apparent optimum level of potassium cannot usually be maintained in animals in which the extracellular level of sodium is below about 140 mM may explain why so many non‐marine animals have internal media of about that concentration, for more concentrated body fluids would require more work for their regulation.

3. In axoplasm, the concentration of potassium is more nearly proportional to the concentration of sodium in the internal medium and this may partly explain the general correlation between the extracellular levels of sodium and potassium.

4. The relation between pH and temperature in poikilothermic vertebrates is such as to suggest that the prime function of acid‐base regulation is to control the ionization of imidazole groups.

5. High tensions of carbon dioxide cannot be maintained in water‐breathing animals because of the high solubility of this gas in water as compared with oxygen. Bicarbonate levels are correspondingly low to give a suitable pH. Higher tensions are possible in air‐breathing animals, and also necessary if water and heat are to be conserved, but an uncertain upper limit is set by the need for oxygen. The associated higher levels of bicarbonate confer the advantage of better buffering.

6. Calcium and bicarbonate levels are not obviously limited by the solubility of calcium carbonate and a more general limitation on the composition of body fluids seems to arise from the low solubilities of calcium phosphates.

7. The pattern of ionic balance in vertebrate plasma, reflected in a nearly constant value to the molar ratio ([Ca] + 5 × 10‐‐4)/([K] +0.034 [Na]), may be explained in terms of the maintenance of a constant electrical gradient across certain areas of cell membrane, between the inner and outer double layers.

8. The patterns of cation balance in the haemolymphs of molluscs, crustacea and insects are also reviewed, with emphasis on the correlations existing between the concentrations of different cations. An attempt is made to relate the correlations in the mollusca to the concentrations of cations at the surfaces of cells.
DEVELOPMENTAL BIOLOGY AND THE STUDY OF MALFORMATIONS
Authors: Hughes A. F. W.
Published: January 2008

1. The scientific approach to malformations began with experimental work on abnormal conditions of incubation in the chick.

2. More precise experiments on causing abnormalities had a common origin with experimental embryology.

3. Progress in experimental teratology during the last fifty years is reviewed in a commentary on the four principles formulated by Stockard in 1921.

4. Some relationships are traced between the results of cytogenetical studies in man and in other organisms.

5. An account is given of present knowledge concerning malformations of the neural tube originating either experimentally, spontaneously, or phenotypically.

6. The teratological implications of some recent theories on the expression of the genotype are discussed, particularly in relation to problems of hormones as teratogens.

7. Some account is given of the implication of carbohydrate metabolism and terato‐genesis.

8. Teratogenesis is possibly related to cationic balance in early development.

9. It is suggested that one factor retarding progress in the understanding of malformations is the tendency towards the development of teratology in an insufficiently close relationship with other branches of cell biology.
GENETIC CONTROL OF VERY EARLY MAMMALIAN DEVELOPMENT
Authors: MAGNUSON TERRY , EPSTEIN CHARLES J.
Published: January 2008

The overall picture of mammalian preimplantation development is one of complex but integrated molecular activity. As development progresses from the 1 cell stage, blastomeres acquire properties that differ from those of cells of previous stages and eventually differ from one another even at the same stage. The evidence concerning the role of the embryonic genome during this process can be summarized under two headings:

(1) Expression of embryonic genome

(a) Quantitative and qualitative changes in RNA and protein synthesis begin to occur soon after fertilization.

(b) Changes in structural proteins (enzyme activities, transport systems and intercellular junctions) occur throughout early development.

(c) Paternal gene products can be detected as early as the 2‐cell stage.

(2) The need for expression of the embryonic genome

(a) Inhibitors of RNA and protein synthesis result in abnormal and lethal development.

(b) Several mutations (T/t, Ay, Os, c25H, Om, Ts) are lethal during early development.

(c) Chromosomal imbalance (monsomy, haploidy, nullisomy) has adverse effects on early development.

Even though studies in vitro on the inhibition of translation indicate that stable maternal messenger RNAs are present in the developing mouse embryo, the evidence outlined in this article strongly supports the belief that embryonic gene expression occurs very early in development (at least by the 2 cell stage) and that this expression is required for normal development.
PHORESY AS MIGRATION ‐ SOME FUNCTIONAL ASPECTS OF PHORESY IN MITES
Authors: BINNS E. S.
Published: January 2008

I. The dispersive role of mite phoresy, which has merely been presumed, is presented in the light of modern theories of migration with the aim of its characterization behaviourally, ecologically and physiologically.

II. Data on phoresy accords well with modern, behavioural definitions of migration, as a phase of the depression of growth‐promoting functions, during which the phoretic mite is transported while it shows a special readiness for being moved.

III. Thus, modern definitions of migration encompass ‘passive’ movements which, none the less, involve active phases of seeking out of the host.

IV. An examination of mite loads suggests that phoresy is most effective where the host gathers within the range of the mite; hence the association of phoresy with micro‐habitats between which the mite requires to be carried. Monocultural plant‐stands and ecological climaxes are not characterized by phoretic associations.

V. The role of phoretic mites in colonization is clarified, in that phoretic migration is associated with sub‐climactic communities. Thus, phoresy is invited where habitats are discrete and temporary, in which case it is manifest, as typical of migration, as a means of colonizing and exploiting irregularly changing habitats byr‐selected, pre‐reproductive individuals.

VI. Waiting‐stages, marked by the depression of growth‐promoting functions, occur within the life‐cycle of the phoretic mite. The ‘hypopus facies' characterize the typical phoretic stage, whose association with the host is an adaptation for survival in extreme environments.

VII. Attachment pattern is a function of specificity towards the host. Structural and behavioural adaptations for attachment are developed and some sensory mechanisms have been shown, as have some physiological relationships with changes in the substrate; these changes also affect detachment.

VIII. That phoresy is not caused by unfavourable conditions but is related to those that allow optimum dispersal is supported by sound evidence.

IX. Physiologically, waiting stages have analogies with diapause which, together with migration, have been characterized by a temporary failure of the migrant to respond, by further growth and development, to the conditions that will eventually promote these processes.

X. With phoresy are contrasted relations, between mite and insect, where the association is assured and more or less permanent.

XI. The study of phoresy is very fragmented. However, a case has now been made for putting the dispersive role of phoresy beyond presumption, so that phoretic associations can clearly be fitted into modern treatments of migration.
COEFFICIENTS OF ASSOCIATION AND SIMILARITY, BASED ON BINARY (PRESENCE‐ABSENCE) DATA: AN EVALUATION
Authors: HUBÁLEK ZDENEK
Published: January 2008

Forty‐three association (similarity) coefficients were collected and evaluated in this survey. Some of them are synonyms or direct correlates with earlier described indices (A8, A9, A12, A31, A33), others are mere transforms from one range of values to another (A10, A24, A33). Several coefficients are incompatible with suggested admissibility conditions of the minimum‐maximum value (A13, A16, A27, A28, A29, A31), symmetry (A1, A2, A13, A16, A26), discrimination between positive and negative association (A27, A28, A31) or monotonicity with (χ2) (A19, to A24); A17 yields very low and erratic values.

As a result, 23 coefficients were excluded and the remaining 20 measures were subjected to an empirical trial on interspecific association data among fungi of the genus Chaetomium, with the use of a cluster analysis. The classification produced five main clusters of related coefficients, with several subgroups. It was then demonstrated that representative indices from different clusters yield different dendrograms of interspecific association among Chaetomium, and A34, A14, possibly also A36 and A40 seemed to be less sensible. A set of measures that generally work well (at least in the interspecific association) comprises A4 (Jaccard), A4 (Dice‐Sφrensen), A7 (Kulczyński), A11 (Driver‐Kroeber‐Ochiai) and, with some reservation A30 (Pearson tetrachoric) and A32 (Baroni‐Urbani‐Buser). For some purposes, however, other ‘admissible’ coefficients would be more optimal, and the choice of a measure should be related to the nature of the data. It is tentatively suggested that three or so alternative coefficients be used and the results compared on the same data basis; moreover, significance tests on association should be carried out whenever possible.
Bacterial Blight of Cotton
Authors: Innes N. L.
Published: January 2008

1. Bacterial blight of cotton is potentially one of the most damaging diseases of cotton.

2. Its symptoms and adverse effect on yield are described.

3. Control measures include: (i) cultural techniques of crop sanitation, and the destruction of crop residues, as well as close seasons and crop rotation; (ii) chemical seed treatments and foliar sprays; (iii) the breeding of resistant varieties.

4. Techniques are described for the breeding of resistant varieties, and sources of useful genetic plant resistance identified.

5. The complex nature of the interactions between host genetic resistance, variation in the pathogen and environment is emphasized.

6. Successful resistance‐breeding programmes in Africa and the USA are reviewed, and attention is drawn to the pressing need for resistant varieties in India and Pakistan.

7. Continued success in the control of bacterial blight will require integrated programmes that include cultural methods, the use of chemicals (particularly as seed treatments) and the cultivation of resistant varieties with durable resistance.
THE FUSION OF SEXUAL NUCLEI
Authors: Szabo Stephen P. , O'Day Danton H.
Published: January 2008

A classification scheme is proposed for the types of sexual nuclear fusion that occur in eukaryotes. The two main classes are envelope fusion and envelope vesiculation and each is further divided into subclasses. The formation of sexual nuclei (pronuclei) has been detailed in representatives from various phyla, but is best understood in animals, in which the development of male and female pronuclei differs in some respects. The only characterized cytoplasmic mediator of pronuclear movement are microtubules. Groups of eukaryotes can be classified according to the type of nuclear fusion they reveal. Envelope fusion occurs in animals whose eggs are fertilized at the pronuclear stage, and in all plants, fungi, protozoa and algae studied to date. Ultrastructural details of envelope fusion have shown variations that are classified in our scheme as direct and indirect, the latter being restricted to the plant kingdom. Envelope vesiculation only occurs in animals, in which it is the most common means of nuclear fusion. Four subclasses can be defined according to the timing of the vesiculation of the nuclear envelopes, and the extent of envelope surface projections prior to fusion. The amount of work reported on the controlling mechanisms of nuclear fusion has been limited, but some evidence of genetic control has been provided, particularly in fungi. Evidence is presented to indicate that the control of the fusion competence of nuclei is a negative one. This review of the information available on nuclear fusion points out the need for extensive future comparative studies if this important process is to be better understood.
BODY FAT, PUBERTY AND FERTILITY
Authors: FRISCH ROSE E.
Published: January 2008

1. The high percentage of fat, about 26–28% in the mature human female, may influence reproductive ability directly through two mechanisms: (a) fat converts androgens to oestrogens; (b) relative fatness influences the direction of metabolism of oestrogen to the most potent or least potent forms. The relative degree of fatness thus is directly related to both the quantity of circulating oestrogen and the biological effectiveness of the oestrogen. This is a neat mechanism for relating rates of growth, nutrition and energy outputs to the energy requirements for reproduction. Fat is the most labile body tissue; it therefore reflects environmental changes more rapidly than other tissues of the body.

2. The slow maturation of the hypothalamus and pituitary up to menarche, or first oestrus, is accompanied by a slow maturation of the body, which changes not only in size but in the relative proportion of bone, muscle, and fat. Evidence is presented that a particular threshold ratio of fat to lean mass is normally necessary for puberty and the maintenance of female reproductive ability in the human and in the rat. The synchronizing mechanisms may be metabolic, relating food intake to core temperature and/or fat storage.

3. Undernutrition and weight loss in the range of 10–15 % of normal weight for height delays menarche and causes amenorrhoea. Ballet dancers and athletes also have delayed menarche and amenorrhoea. The cessation of reproduction in both groups can be considered adaptive. Refeeding and/or cessation of intense activity results in the initiation or resumption of menstrual cycles after varying periods of time. A necessary threshold weight for height can be predicted from a fatness index.

4. Differences in the natural fertility of historical and contemporary populations may be explained by a direct effect of food intake and energy outputs on fecundity.

5. The late maturing fat ‐ ‘sex fat’ ‐ may have a special role in reproduction.
CELL SELECTION IN DEVELOPMENT
Authors: MICHAELSON JAMES
Published: January 2008

Cell selection is recognized to be the principal mechanism in the generation of the immune response. The role of cell selection in other developmental systems is considered here, with emphasis on the morphogenesis of the vertebrate limb, the formation of pigment pattern in the pelt of mammals and the changes that occur in the human erythrocyte at the time of birth.
STRUCTURAL AND ULTRASTRUCTURAL FEATURES OF CORTICAL CELLS IN MOTOR ORGANS OF SENSITIVE PLANTS
Authors: FLEURAT‐LESSARD PIERRETTE
Published: January 2008

(1) The movements are only expressed in motor cells, regardless of the nature of the stimulation or its point of application. Therefore, these cells have structures capable of traducing the different stimulation‐induced messages which are received in parts incapable of movement.

(2) K+, Cl‐ and Ca2+ are the major ions. Their fluxes have been followed during nyctinastic movements as well as during stimuli‐induced movements. At the moment, the location and the role of these ions are being studied.

(3) The movement results from the integrated activity of all (n) motor cells in the pulvini (i.e. n > 350 × 103 in primary pulvini 3 mm long and 1·9 mm thick).

(4) The motor cell is a full‐grown cell whose osmotic activity induces turgor variations allowing foliar movements.

(5) The motor cell is a highly differentiated cell, which, up to now, has never been able to dedifferentiate in order to produce callus.

(6) The motor cell has original features in its apoplastic compartment (large meatuses, wall foldings, large periplasm with membranes) and in its symplastic compartment (double vacuolar apparatus, morphological polarity given by the tannin vacuole location near the nucleus, abundant mitochondria).

(7) Its cytoskeleton includes microtubules, cytoplasmic and vacuolar fibrils (in particular in the tannin vacuole), and a wall with special properties.

(8) The motor cell is supposed to contain contractile proteins, whose nature and location are being investigated.

(9) The shape change of the motor cell is obvious after pulvinar bending. This change is probably associated with a volume change in several intracellular compartments (vacuole, mitochondria, vesicles).

(10) At the cellular and subcellular level the same general features are observed in motor cells of non‐seismonastic and of seismonastic species. Probably, functional differences depend upon differences occurring at the molecular level.

(11) The motor cell is an interesting model for the study of the osmoregulation mechanism in plant cells, to test the effect of toxic products, in particular to find their optimal efficiency in the circadian cycle.
THE FUNCTIONAL ORGANIZATION OF FILTRATION NEPHRIDIA
Authors: RUPPERT EDWARD E. , SMITH PETER R.
Published: January 2008

(1) Based on the classical studies of Goodrich, protonephridia are believed to be phylogenetic antecedents of metanephridia. It is argued here that the primary factor determining the type of nephridium expressed is body size rather than phylogenetic status.

(2) The proposed model defines a nephridium functionally and predicts two general configurations for filtration nephridia in animals.

(3) Application of the model to metanephridial and protonephridial systems indicates differences in the sites of ultrafiltration and mechanisms of pressure generation.

(4) Metanephridial systems function by muscle‐mediated filtration of vascular fluid into a coelomic space before modification by an excretory duct.

(5) Protonephridial systems function by cilia‐mediated filtration of extracellular fluid into the lumen of a protonephridial terminal cell before modification in an adjoining duct.

(6) The model predicts a correlation between animals with blood vessels and metanephridia, and animals without blood vessels and protonephridia. The correlation is shown to be nearly perfect.

(7) Exceptions to the model are discussed.

(8) Original experimental evidence is given for the permeability of the protonephridial terminal cell to iron dextran and its reabsorption by the protonephridial duct in the polychaete, Glycera dibranchiata.

(9) Experimental data for proto‐ and metanephridial systems are summarized and shown to support the proposed model.

(10) The ultrastructure of the exceptional amphioxus ‘protonephridium’ is reviewed and original data are presented. Its organization is structurally and perhaps functionally intermediate between proto‐ and metanephridial systems.

(11) An original ultrastructural comparison is made of monociliated nitration cells in a size range of larval invertebrates from five phyla. Filtration cells that are structurally intermediate between protonephridial solenocytes and metanephridial podocytes are noted in larvae intermediate in body size between the two extremes. The comparative data suggest that (i) podocytes and solenocytes are homologous cells and (ii) that body size is correlated with which of the two designs is expressed.

(12) The fates of larval podocytes are followed through metamorphosis in three species. The results confirm the equivalence of podocytes and solenocytes as suggested by the comparative analysis. They further indicate that which morph is expressed is a function of body design factors discussed in the model.

(13) Protonephridia are believed to be primitive to metanephridia because they occur in presumably primitive animals and in ontogenetic stages of many animals with metanephridia as adults. It is suggested here that the distribution of protonephridia is related to small body size and the lack of blood vessels, regardless of phylogenetic status. The occurrence of protonephridia in the larvae of species with metanephridia as adults is explained similarly as a function of the small larval size and lack of blood vessels.
HISTOLOGICAL STAINING OF LIPIDS FOR THE LIGHT AND ELECTRON MICROSCOPE
Authors: WIGGLESWORTH V. B.
Published: January 2008

1. It is generally agreed that the blackening of osmium tetroxide by unsaturated lipid is too unpredictable to demonstrate lipid in tissues.

2. At neutral pH osmium tetroxide combines with the double bonds in the lipoproteins of cellular membranes (mitochondria, etc.) and the deep colour reaction of ethyl gallate with this osmium provides good staining of lipid for the light microscope.

3. Osmium taken up by tissue proteins at neutral pH is only a small fraction of that taken up by the lipid. (After acid fixatives osmium tetroxide is a general protein stain.)

4. The uptake of Sudan black B by partition from dilute solution is a specific test for lipid, but in normally fixed tissue most of the structural lipid is ‘bound’ and is not accessible to the dye.

5. Cautious treatment of fixed tissue with dilute sodium hypochlorite will unmask this lipid for viewing by the light microscope.

6. Direct fixation with neutral osmium tetroxide is an effective method for visualizing lipid for the electron microscope (as in the ethyl gallate method for the light microscope). But the poor penetration of osmium limits its use in this way.

7. After formol/glutaraldehyde fixation much of the lipid in the tissues is ‘bound’ and does not take up osmium. It can be unmasked by a saturated aqueous solution of thymol.

8. The unmasked lipid can then be rendered more osmiophil by partition in a solution of the highly unsaturated terpene farnesol, thus increasing the uptake of osmium in a renewed application.

9. Some of the novel observations on tissue lipids made by these methods are reviewed.
ADAPTATIONS OF TERRESTRIAL ARTHROPODS TO THE ALPINE ENVIRONMENT
Authors: SØMME LAURITZ
Published: January 2008

1. The climate changes drastically above the timberline. Diverse adaptations have been evolved by insects and other terrestrial arthropods to survive the alpine environment. The fitness of each species depends on a combination of different factors in accordance with their special habitats.

2. Morphological adaptations such as reduced body‐size, are known from a number of alpine insects, increasing their possibility to find sheltered microhabitats. Selection for reduced body size in Andean Phulia spp. butterflies is probably a result of their rigorous environment. Wing atrophy, which is also known in insects from other extreme environments, is widespread in alpine species. In several terrestrial arthropods the absorption of solar radiation is increased by melanism. Increased pubescence, protecting against the loss of heat, is known in alpine butterflies and bumblebees.

3. Several behavioural adaptations are described. Thermoregulatory behaviour is important in many species to raise their body temperatures. Alpine butterflies orient the dark basis of their wings perpendicular to the rays of the sun. Body temperatures of 30 °C may be required for flight. To increase their activities many alpine terrestrial arthropods seek warmer microhabitats in the vegetation and under rocks. The adaptive advantage of nocturnal activity as observed in several species, may be to maintain the water balance or to avoid predation.

4. Tropical alpine terrestrial arthropods are faced with special problems. The large diel temperature fluctuations require cold‐hardiness during the night and tolerance to heat during the day. Many species seek sheltered microhabitats under rocks and in vegetation.

5. Due to low precipitation and high evaporation rates many mountain areas are extremely dry. High resistance to desiccation may be very important to alpine species, and in particular to tropical species. Rates of water loss at low relative humidities are comparable to those of desert arthropods.

6. As an adaptation to the cold alpine summers several species of terrestrial arthropods require more than one year to complete their life‐cycles. Special to these species is their adaptation to low temperatures in two or more overwintering stages. In spite of their cold surroundings several species have univoltine life cycles, frequently combined with highly specialized adaptations. Increased metabolic rates as a compensation to low temperatures may be widespread in alpine species, but few data are available.

7. Cold tolerance is of particular importance in temperature alpine species. Winter survival in Collembola and Acari depends on supercooling. Great seasonal variations have been observed in a number of species. Freezing tolerance is also known from alpine insects, e.g. in some species of beetles. At high latitudes alpine species must endure periods of up to eight or nine month at low temperatures during hibernation. Anaerobiosis is known from species that are enclosed in ice, with lactate as the main end product of metabolism.
EXPERIMENTS ON THE LIMITATION OF BIRD NUMBERS BY TERRITORIAL BEHAVIOUR
Authors: NEWTON I.
Published: January 2008

(1) This paper examines removal and other experimental studies on the role of territorial behaviour in the limitation of bird densities. Experimental design is discussed, as are the types of conclusions that can be drawn.

(2) Experiments have been conducted on more than 40 species from a wide range of taxonomic groups. Most provided evidence for density limitation, probably mediated by territorial behaviour, and for the existence of a non‐territorial sector able to take territories when territory owners were removed or when additional habitat was made available. Experiments in the breeding season indicated that some surplus birds, although younger on average then territorial birds, were sexually mature and able to breed when given the chance. In some species, replacement birds bred less well than other territorial birds, but in other species no difference was apparent between the two groups.

(3) Other experiments indicated that, while density was limited by territorial behaviour in good habitats, this was not the case in poor habitats, and that some individuals would move from poor to good habitat when territory owners were removed from good habitat.

(4) In some species, non‐territorial birds of breeding age were present in the population despite the existence of vacant territorial sites, while in others replacements were observed on good territories but not on poor ones. The implications were that site quality influenced whether settlement, defence and breeding occurred, and that some individuals had more stringent site requirements than others. In some seabirds' sites in the centre of a colony were more attractive than sites on the edges.

(5) Many land‐bird species that have been studied show two peaks of territorial activity each year, in autumn and in spring, and a limitation on breeding density can occur at either or both seasons, depending on conditions.

(6) The fact that densities of many bird species fluctuate greatly from year to year is not inconsistent with the limitation of density by territorial behaviour. Several mechanisms are apparent through which density might be limited by territorialism at different levels in different years, so that surplus non‐territorial birds are present in years of low territorial density, as well as in years of high territorial density.

(7) Experiments have shown that density is limited by the presence of territorial birds, in some species at different levels in different areas or years. The next step is to find whether density is regulated by the presence of territorial birds over a period of years in a density‐dependent manner. For this, observational data are required to find whether the proportion of birds that is excluded by territorial behaviour each year varies with the total number available for settlement. Such studies can be made only on species in which non‐territorial birds can be counted accurately, as well as territorial ones.
ON THE GENERATION OF FORM BY THE CONTINUOUS INTERACTIONS BETWEEN CELLS AND THEIR EXTRACELLULAR MATRIX
Authors: ETTINGER LIA , DOLJANSKI FANNY
Published: January 2008

The central issue of this essay is the problem of how multicellular organisms develop and maintain the complex architecture and intricate shape of tissues and organs. The concepts pattern formation, morphogenesis and differentiation are defined and discussed suggesting a distinction between processes that underlie uniformity (e.g. basic body plans) and those underlying inter‐ and intra‐species variation. The initial stage of limb bone development ‐ the formation of the mesenchymal condensation — is described in detail. On the basis of these data and many additional examples from other developmental systems, the central role of continuous cell‐ECM interactions in the generation of form is deduced. Evidence is provided as to the leading role of the mesenchymal‐fibroblast‐like cells in sculpturing tissue and organ architecture. It is proposed that a group of cells within their ECM, rather than the single cell, is the functional unit relevant to the generation of form.

The continuous cell‐ECM interactions lead to the generation of form not by a detailed obligate pathway, but rather by a process of ‘selective stabilization’ (Kirschner & Mitchison, 1986), i.e. a gradual organization into more stable structures, where existing structural configurations serve to increase the likelihood of certain configurations and reduce that of others. Data are quoted to support the notion that even cell division does not erase all the structural information imprinted in the cell. The role of the metazoan genome in morphogenesis is discussed in the light of the process of selective stabilization.
THE RELATIVE IMPORTANCE OF SHORT‐ AND LONG‐RANGE MOVEMENT OF FLYING APHIDS
Authors: LOXDALE HUGH D. , HARDIE JIM , HALBERT SUSAN , FOOTTIT ROBERT , KIDD NEIL A. C. , CARTER CLIVE I.
Published: January 2008

1. Aphids are notorious pests of world agriculture. Even so, uncertainty persists as to their capacity for successful aerial dispersal. Evidence exists that, under some conditions, aphids can be wind‐borne over long distances, i.e. hundreds of kilometers over desert or sea. It has been argued, in the recent past, that this phenomenon may be part of a strategy to locate fresh host plants in new distant areas. However, the proportion of these insects successfully colonizing new hosts is unknown.

2. Other work using meteorological backtracking has also indicated long‐distance movement, but the accuracy of such predictions is dubious unless the altitude of transport is known. Mark‐releaseecapture experiments with such small insects have limited potential due to large dilution effects. Static ‘snap‐shots’ of demographic population densities, using suction traps, cannot accurately distinguish local aerial density fluxes and population movements from a distance. However, genetic and physiological markers may provide more direct information on population mixing; for example, some allozyme studies have shown a limited level of inter‐population gene flow.

3. Under suitable conditions, aphids take off, maintain flight and alight in response to the appropriate visual and olfactory cues. Undoubtedly successful long‐distance movement occurs from time to time, but its ecological relevance may have been overstated in the past. It may be selectively disadvantageous for aphids to move from areas containing their host plants. In contrast, it is advantageous for aphids to maximise their chances of survival and reproductive success by landing on suitable plant hosts at the earliest opportunity.

4. The clonal nature of aphids (a single genotype may comprise vast numbers of individuals) means that there may be advantages to phenotypic variation between individuals in the readiness to move. Recent evidence indicates that such a variation exists in the duration of the behavioural migratory phase, the initial period of maiden flight when host‐plant cues are ignored and when landing is inhibited.

5. The relative biological importance of short‐ us. long‐distance movements is reassessed with reference to plant virus epidemiology and the spread of new genotypes, e.g. insecticide resistance. It is concluded that the biological relevance of short‐distance movements have a much greater impact on population and genotype distribution than long‐distance movements, which may be comparatively infrequent.
THE STRIPED COLOUR PATTERN AND STRIPED/NON‐STRIPED POLYMORPHISM IN SNAKES (REPTILIA: OPHIDIA)*
Authors: WOLF MOSHE , WERNER YEHUDAH L.
Published: January 2008

The occurrence of striped colour patterns and of striped/non‐striped polymorphism systems among snakes is reviewed from literature data augmented by some personal observations. Among 1367 species, 190 were striped or had striped morphs. Of 11 families, the striped pattern was common mainly among Colubridae, presumably in relation to the active escape behaviour strategy, prevalent in this family. The striped species tended to cluster in a small number of genera.

The 40 striped/non‐striped polymorphism systems found, fall into five categories, according to the coloration patterns of the alternative morphs: (I) blotched (cryptic); (2) barred (or ringed); (3) plain; (4) melanistic; (5) albinistic. Most polymorphisms are presumably maintained by eco‐behavioural trade‐offs, depending on the category and on the habitat: The striped morph is presumed more effective in active escape and sometimes also in camouflage; the alternative morph may be more effective in camouflage, in active escape or in thermoregulation. Hence morph frequency depends on the habitat. Striped‐albinistic polymorphism in Elaphe climacophora presumably depends on human protection of the albino morph.
THE REGULATION OF ALTERNATION OF GENERATION IN FLOWERING PLANTS
Authors: Dickinson By H. G.
Published: January 2008

The developmental changes involved in the alternation of generation represent the major gene‐switching events in the life history of plants. While a large number of genes are common to both sporophyte and gametophyte, many thousand sequences are specifically expressed in each generation; indeed, certain key constituents (e.g. tubulin) are encoded by different genes in each generation, indicating that sporophyte and gametophyte are responding to different evolutionary pressures. Evidence is accumulating that major gene‐switching events in plants, such as flowering, are regulated by complex control systems which ensures that development occurs only in the correct groups of cells at the appropriate time. A similar, or more sophisticated system might thus be expected to regulate alternation of generation. It is not possible to manipulate alternation of generation in a similar fashion to flowering, but study of apparent aberrations of development occurring in nature and in vitro suggests that alternation only occurs in cells which have become competent to receive particular developmental stimuli. Further, in certain cases, competent cells may be switched either into sporophytic or gametophytic developmental pathways depending upon the nature of the stimulus. Acquisition of competence seems to involve isolation of cells from the symplast, some cytoplasmic dedifferentiation, and perhaps cell cycle arrest or transition. The stimuli in vivo appear metabolic in nature, although embryogenesis may be activated by specific classes of glycoproteins. Interestingly, examination of agamospermic systems suggests that fertilization of the egg per se is not the signal which activates sporophytic development. Once competent cells have received the stimulus they start to develop, with no delay in a ‘determined’ state. Sporophytic and gametophytic development in vivo and in vitro both start with an asymmetric division, except for the female gametophyte which may arise via a range of developmental pathways, depending on the species.