摘要:

SUMMARYThe Ptilonorhynchidae (bower‐birds) and Ailuroedidae (cat‐birds) are families widespread throughout Australia and New Guinea and endemic to these regions. Only bower‐birds make bowers. The bower is on the ground and has no direct connexion with the nest, which is built in a tree that may be some hundreds of yards away. At each bower is a display‐ground which the owner strews with coloured flowers, fruit and shells, or, in some species, pallid or reflecting articles. These, contrary to general belief, are selected with great discrimination. Members of three genera paint their bowers with fruit‐pulp, or with charcoal or comminuted dry grass mixed with saliva. Cat‐birds, on the other hand, do not erect a special structure.Pioneer nineteenth‐century naturalists, who knew little about bower‐birds, ascribed a courtship function to the above activities and postulated an aesthetic sense as well. During the last three decades, however, there has arisen a school of Australian naturalists, which, though admitting that the displays of bower‐birds may have had their origins in sexual utilitarianism, believe that this has become a minor factor. They hold that modern bower‐birds are intelligent, consciously aesthetic, and that they carry out their complex display activities essentially for relaxation or recreation. This theory is here rejected. Experimental work has shown that gonadectomy inhibits display and bower‐building and that injections of testosterone re‐establishes it. Post‐nuptial (out‐of‐season) display occurs after the seasonal metamorphosis of the testes and the rehabilitation of the interstitium, and is of the same nature as the autumnal display of other birds.Excluding one monospecific genus(Archboldia) of whose bower only fragmentary knowledge is available, true bower‐birds appear to fall into two distinct groups. These are (i) the avenue‐builders(Ptilonorhynchus, Chlamydera, Sericulus) (Fig. i) and (2) the maypole‐builders(Prionodura, Amblyornis) (Fig. 2).Theavenue‐buildersare widespread throughout both Australia and New Guinea. Each lays down a foundation platform of twigs, and in this wedges twin parallel walls of twigs which sometimes arch overhead. At one, or sometimes both, ends of the bower the male birds arrange their display‐things. One species replaces the terminal display‐grounds with two additional walls which are built at right angles to the original ones. It thus achieves three avenues, in all of which it places decorations.Among avenue‐builders the male builds a bower early in the season, after which it attracts a female to the bower and there displays to it at the focal point of its territory. The male rapidly achieves spermatogenesis but the female cycle lags behind. The male displays (‘dances’) for several months, while the female remains passively in waiting. During this lengthy period of androgen liberation there occurs the remarkable display of bower‐painting, vocal mimicry of other birds, and the insatiable collection of coloured or otherwise distinctive display‐things. In one, and possibly several, species the collected display‐objects are coloured similarly to the watching female. With these in his beak the male displays energetically and often violently but does not approach the female. This has led to published references to ‘sexual fetishism’ in bower‐birds. There is, however, a fundamental difference between the above normal and constant avian activity and a form of psychopathic sexual behaviour in man. Likewise, although the male bower‐birds' prolonged preoccupation with display‐objects while he is in a breeding condition involves a form of sexual sublimation, it is important to remember that this too is normal and constant and a means towards, rather than a sublimation of, reproductive efficiency. The display with the ornaments before the watching female continues unabated until the forest becomes seasonally full of the special protein food on which the young are fed. Then only is the male's physical attention transferred from his display‐things to the waiting female. The female now leaves the bower, alone to build the nest and to rear the young. The male continues his display. His testes, unlike those of most birds, do not metamorphose after the young appear. Thus he remains potentially polygamous, although polygamy has not been proved.In ascribing an essentially utilitarian function to the bower and associated activities, it is not suggested that bower‐birds do not enjoy their extraordinary performances. Further, it is emphasized that bower‐birds appear to have developed their display beyond the bounds of strict utilitarianism, since some individuals successfully reproduce without painting their bowers, and it has been experimentally shown that reproduction (in the aviary without competition) can take place in the absence of coloured decorations.Themaypole‐builders,with one exception, are confined to the dense rain‐forests of New Guinea. The fundamental maypole structures are a central growing sapling with a cone of fabric packed around its base. One species, measuring only 9I inches long, extends this cone to a height of about nine feet. Another species surmounts a dwarf cone with a conical, waterproof hut. A third builds over the cone a hemispherical hut fronted by a stockade, and a fourth surmounts the basal cone with a cylinder of moss and fibre which extends up the basic sapling. Fruits, flowers, beetles' wing‐cases and other coloured objects are used to decorate various parts of the structures or their surroundings.Bower‐building of both avenue and maypole types probably originated as a form of displacement activity. The males as well as the females of most passerine birds possess an inherent urge to build nests. To‐day only female bower‐birds seem to build nests. These are built of twigs. The males, on the other hand, have taken to building twig bowers on the display‐ground. Here they spend much of their time during the sexual season. The display‐ground is the focal point of their activity, and, together with the female, of their interest. Nest‐building among females is essentially controlled by the seasonal liberation of hormones. The same appears to be true of male bower‐building. In short, nest‐building is of a bisexual nature, and this has made possible bower‐construction as a displaced building drive, the new product of which has become valuable, ritualized and permanent in the course of the evolution of each species.Bower‐painting is a displaced form of the courtship feeding that is widespread among passerine and other birds. Instead of projecting this attention on the watching female the male does so on his bower which, along with its decorations, is his chief physical preoccupation (apart from feeding and threat) during the weeks or months of spermatogenesis.Of the threecat‐birds,two greenish species indulge in arboreal displays in much the same manner as other passerine birds, whilst the third, the brown stagemaker of tropical Queensland, has taken partly to the rain‐forest floor. Here it clears a space on the ground and covers this with fresh leaves which it cuts each morning by means of a ‘toothed’ beak. The leaves are placed with paler under‐surfaces uppermost, thus creating the more striking effect against the dark earth. From a singing‐stick above the decorated stage the bird calls loudly and continuously and thus advertises its presence and its decorated stage to every potential mate or rival within many hundreds of yards. The precise function of the stage is unknown, but the scanty available data suggest that it, and the vocal display from above, are means toward the cementing of the pair‐bond and effecting the synchronization of the joint sexual processes of the pair. Finally, perhaps, it is the mating place when the monsoon begins and brings with it the seasonal harvest of insect food on which the young will be fed.It has been suggested by cabinet‐workers that ‘bower‐building has been developed coincidentally or perhaps independently’ (Iredale, 1950) and

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1954.tb01395.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1954.tb01396.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

摘要:

SUMMARYDuring the last ten years the differentiation of the primary vascular tissues has been intensively studied in plants developing normally and in those that were treated experimentally.The untreated plants were mainly seed plants. Several critical studies of dicotyledons and gymnosperms have shown that the procambium in vegetative shoots is delimited among the derivatives of the apical meristem in continuity with the vascular tissue in the mature part of the axis; that is, it differentiates acropetally. This procambium appears in the form of strands positionally related to leaves, that is, as leaf traces. The differentiation of procambial cells into phloem cells occurs acropetally and generally continuously. The first xylem, on the other hand, matures in or near a leaf and then differentiates basipetally in the axis and acropetally in the leaf. In the roots of seed plants procambium, phloem and xylem differentiate acropetally and continuously.The procambium shows initial unity in the root‐hypocotyl‐cotyledon system of the embryo and seedling, but the course of differentiation of the xylem and the phloem does not necessarily duplicate the initial course of the procambium. The procambial connexion between the epicotyl and the hypocotyl may also show initial continuity.The establishment of vascular connexion between an axillary or adventitious bud and the parent organ varies in relation to the time of development of buds. Those that develop close to the apical meristem of the parent shoot may show initial vascular continuity with the latter. Others are usually separated by vacuolated parenchyma from the vascular tissue of the parent organ and may initiate their procambium independently.The information on vascular differentiation in vascular cryptogams is meagre. There is evidence, however, that in microphyllous representatives the main part of the vascular system of the shoot differentiates independently of the leaves.The experimental studies that were used to interpret primary vascular organization consisted of removal of young leaf primordia, of partial isolation of apical meristems by vertical incisions, and of division of apices into sectors by radial longitudinal cuts. These studies were carried out on ferns and dicotyledons.The defoliated parts of axes had vascular systems in the form of relatively compact cylinders or even solid cores. The partially isolated apical meristems gave rise to shoots with normal leaf arrangements. The initial vascular connexion of these shoots with the axis below occurred, in the dicotyledons, by a basipetally differentiating procambium. In the ferns such connexion was usually absent. The dissected shoot apices regenerated one or more new shoots. The manner of connexion of these regenerated shoots with the axis was apparently more complex and more varied than in the partially isolated shoots.The deductions drawn from the experimental studies regarding primary vascular organization were, first, that the apical meristem of the shoot induces the development of the primary vascular system; secondly, that this induction occurs independently of the leaves but that leaf development may later affect the form of the differentiating vascular system; and, thirdly, that the vascular system of the stem of megaphyllous plants consists not only of leaf traces but of cauline tissue as well. These deductions are for the most part hypothetical because they are not based on critical histogenetic evide

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1954.tb01397.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

摘要:

SUMMARY1. Fluctuations of the numbers of aphids in the air have been regarded in the past as due mainly to weather‐controlled changes in flight behaviour. Migration has been envisaged largely as a calm‐weather phenomenon, whose intensity is limited mainly by the effects of wind‐speed on take‐off behaviour. I have called this the ‘flight‐activity hypothesis’; it developed from both laboratory and field work and has been in vogue for about 20 years.2. This hypothesis does not fully explain changes in numbers of aphids in flight. It is apparently inconsistent with the idea of large‐scale windborne migrations. Many other discrepancies are discussed.3. When studying the changes in numbers of aphids migrating, it is helpful to distinguish between aphids migrating from plants on which they bred and those flying from other places subsequently. Aphids from these two classes together make up the general aphid population in the air. The failure to make this distinction in the past and to appreciate that the factors controlling the numbers flying in the two classes are very different, has led to much confusion.4. A new hypothesis of numbers ofAphis fabaemigrating is developed. But it is at present restricted to those flying from breeding sites; in this respect it is considered to be applicable to many species of aphids. The sequence of events is briefly thus: moulting of the winged nymphs into alatae is usually most intense early in the morning; usually one or more additional moulting peaks occur later in the day. The alatae reach flight maturity usually within 24 hr. after moulting. They then usually fly away in ‘flushes’, on the first migratory flight. The numbers in each ‘flush’ depend on the sizes of previous moulting peaks and on the lengths of both the obligatory period for maturation and on the facultative period which follow; thus the effects of vagaries in flight behaviour tend to be obscured. Therefore, the process is only weakly correlated with current weather factors.The numbers of aphids on subsequent flights will also depend on previous population (moulting) changes as well as on behaviour. Aphids lose their ability to fly owing to autolysis of the flight muscles a few days after they have left the original host, and the rapidity with which this occurs will exert a considerable effect on the numbers of aphids on flights subsequent to the first migration and on their ability to spread virus diseases; the quality of their flight may also be affected.Little is known of the biology of aphids after the first migratory flight, nor of the relative effects of the factors affecting their numbers in the air.5. It is suggested that a considerable proportion of all the aphids in the air are on their first migratory flight; and that the number on subsequent flights may be more limited than seems to have been envisaged.6. The flight‐activity hypothesis is reviewed critically and in detail. Its defects are mainly three‐fold.(a) High local concentrations of aphids occurring in occasional calm periods have been thought to account for most of the aphids migrating. This is not so. Most migration is made up of the lower densities on the more numerous windier occasions.(b) Changes in numbers of aphids in the air from day to day were thought to be due mainly to variation in flight behaviour. They are, in fact, mainly collective‐population changes and subject to different laws than those applying only at the individual level.(c) Errors in measurement and treatment of data.The data of the previous authors are analysed in detail, to illustrate these errors and to disprove some previous contentions.7. Various aspects of aphid dispersal are discussed in the light of old and new hypotheses; these are population change and migration; active and passive flight; migratory and non‐migratory flight; the supposed effects of humidity; so‐called ‘optimum conditions’ for flight. The significance of these aspects to the spread of virus diseases is continually borne in mind.It is a pleasure to acknowledge the help from discussions which I have had with my colleagues Dr J. S. Kennedy, Dr L. Broadbent, Mr L. R. Taylor; also Dr E. Haine and Mr Bruce Johnson who, in addition, have helped respectively with translations and

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1954.tb01398.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1954.tb01399.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY