摘要:

Summary1. The endocrine glands of vertebrates develop from all three germ layers; those arising from ecto‐ and endoderm produce hormones of an amino‐acid or polypeptide‐type, while those arising from the mesoderm secrete hormones of a steroid nature.2. All mesodermal glands and a single endodermal gland, the thyroid, are under hypophyseal control.3. All pituitary‐controlled endocrine glands act upon morphogenetic processes after a certain stage of phylogenesis, and the same applies to the directly‐acting hypophyseal hormone STH. It follows that the pituitary acts not so much as the ‘conductor of endocrine glands’ in general, but as the central regulator of morphogenetic processes in particular.4. Incorporation of the thyroid gland into the morphogenetic system took place at the phylogenetic level at which its morphogenetic role came to the fore in processes of metamorphosis.5. The other main hormone system, the adaptive system, includes all endocrine glands of ecto‐ or endodermal origin. These account for short‐term homeostatic regulation and depend on the pineal body for higher control.6. While hypophyseal regulation is stimulatory and is operated through a precise feed‐back mechanism, regulation by the pineal body is more primitive and inhibitory, with minimal indications of feed‐back. The influence becomes stimulatory only in those instances in which the target glands are controlling the same function in an opposite manner, e.g. the parathyroid and the C‐cell. The pineal influence also inhibits the function of the thyroid, and hypophyseal stimulation becomes superimposed on this inhibitory effect, in accordance wit

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1977.tb00835.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Summary1. The first quantitative studies of production on coral reefs were those of Sargent&Austin who showed that productivity on reefs was considerably higher than in surrounding waters. This high production occurred in spite of nutrient limitation and low productivity of offshore waters. Their conclusions have since been confirmed by numerous other workers in both the Atlantic and the Pacific.2. Primary production on reefs has been studied by flow respirometry, measuring changes in oxygen or carbon dioxide concentrations in water flowing over reefs. Production of benthic organisms has also been measured in situ by light and dark bottle methods and by radioactive tracer techniques. Production values obtained by the various methods are not identical but their use in combination is to be recommended.3. Rates of gross primary production on reefs vary between 300–5000 gC/m2/yr. These rates are higher than general oceanic values and as high as those of the most productive marine communities.4. Sources of primary production include fleshy macrophytes, calcareous algae, filamentous algae on the coral skeletons or calcareous rock, marine grasses and the zooxanthellae within coral tissue. Production values from the various sources fall within the range of production of reefs as a whole.5. Concentrations of nitrogen and phosphorus in waters flowing over reefs are consistently low. There is evidence to suggest that both these nutrients are recycled rapidly on the reef and that nitrogen is fixed by bacteria and primary producers.6. In many instances the mass of detritus over coral reefs exceeds the biomass of zooplankton. While the quantitative significance of detritus as food for corals and other benthic organisms has not been evaluated, there is a growing body of evidence to show that this may be the key to understanding secondary production.7. Opinions differ on the adequacy of zooplankton in satisfying the food requirements of corals and other benthic invertebrates on reefs. The weight of evidence suggests that while there is a removal of zooplankton by benthic organisms, the total biomass carried over the reef is too small to support the energy needs of secondary production.8. Bacteria are a potential source of energy for secondary production on reefs and are implicated in nitrogen fixation, decomposition and biogeochemical cycling.9. There is an abundance of sessile invertebrates other than corals on reefs but there are few quantitative data on their importance in secondary production.10. The biomass of fish on reefs may be very high but the quantitative significance of grazing and predation is not fully established.11. Studies on the growth of corals themselves have been based on measurements of skeletal accretion. These methods do not lead directly to estimates of reef organic production. Growth rates of corals vary considerably between and within species.12. Estimates of reef growth have been made from measurements of coral growth and from the flux of calcium carbonate. There is less quantitative information on erosion caused by mechanical damage, by boring organisms and by human pollution.13. Hydrographic factors influence growth and form of reefs and there is some evidence to show that production is enhanced by conservation of water in lagoonal area

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1977.tb00836.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1977.tb00837.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Summary1. The wood of trees grown in temperate regions shows a periodicity in the form of rings which, with certain known exceptions, accurately reflects the annual cycle of the seasons. The wood thus has a built‐in dating system.2. Tree rings are not always the same width in successive years; the widths show a positive correlation with variations in environmental factors.3. Trees in a given geographical area influenced by the same environmental conditions show similar patterns in their ring sequences and may thus be cross‐dated.4. Ring sequences from cross‐dated trees may be used to construct long, accurate chronologies. This practice, the science of dendrochronology, is now so reliable that it is widely used in archaeology and has also served to calibrate the14dating method.5. The extent of the variation in a ring sequence may be expressed in the form of a coefficient known as the mean sensitivity.6. The climatic effects recorded in the growth rings are those which operate at certain crucial periods, such as the growing season. The effects are primarily those of rainfall and temperature; humidity is usually only secondary.7. Damage by insects or fire may be dated by examination of ring sequences.8. As tree‐ring sequences correlate positively with contemporaneous meteorological data, they may be used in the reconstruction of past climates. This is the basis of extrapolatory dendroclimatology.9. New isotope techniques have been developed which indicate the possibility of deducing the ambient temperature of the tree's environment whilst its wood was being formed.10. Interpretative dendroclimatology aims to deduce from the features of a sample, or preferably from a number of samples of wood, the nature of the climate which influenced their development.11. The wood of most growth rings is divisible into two zones, earlywood and late‐wood. The former consists of larger, thin‐walled cells while in the latter the cells are smaller and thick‐walled.12. Beams of light, X‐rays and β‐rays have been used in various instruments to determine the earlywood‐latewood ratio.13. The earlywood‐latewood ratio is dependent upon genetic as well as climatic factors. Of the latter, summer rainfall is the most potent in producing latewood.14. The ring‐width data from a number of Recent and fossil wood specimens have been analysed to show that certain deductions may be made about the climate in which they were formed.15. A histogram technique has been devised to show differences between wood specimens with otherwise similar coefficients.16. Evidence has been produced in support of earlier work to the effect that ring‐width sequences from different radii of a tree trunk have fundamentally similar features, thus demonstrating ‘circuit uniformity’.17. The interpretation of the features of tropical woods is more complex. The mode of development of such a wood is the resultant of the interplay of genetical factors, endogenous rhythms and slight variations in environmental conditions.18. There is evidence that endogenous rhythms are also involved in the development of woods in tempera

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1977.tb00838.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1977.tb00839.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Summary1. The maximum possible efficiency at which living systems are able to convert input nutrients to their own biomass is between 70 and 80 %.2. Conversion efficiency in bacteria, protozoa and metazoan cells in culture approximates more closely to 60%.3. Conversion efficiency during embryonic development begins below 60% and rises above this level in the later stages.4. Very young, post‐natal organisms have high net efficiencies; 50 to 70% in homeotherms and 50 to 80 % in poikilotherms.5. In cellular systems, capable of proliferation, conversion efficiency is independent of food supply. This means that conversion is directly dependent on nutrient supply.6. Control of growth at the tissue level may occur through the control of the supply of nutrients to the tissues and its entry into the cells.7. Compensatory growth, after and during undernutrition, involves increased absorption efficiency and reduced metabolic cost

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1977.tb00840.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY