摘要:

SUMMARYIn the studies to which this paper is an introduction, the genusAcacia(‘Wattles’, in Australia) will be carefully revised, the aim being to establish a phylogenetic classification of the genus as it occurs in Australia.Previous classifications are regarded as too static in conception. These Studies will seek to develop a kinetic conception.Features of the genus have a bearing on the theories of carpel polymorphism (Saunders), phylloclade legume (Thompson), leaf forms (Zimmermann).The position of the genusAcaciain the Leguminosae is briefly reviewed.The existing classification of the genus is found to be usually made with foliar or other vegetative features as the first principle of division. This is regarded as unsatisfactory.The contemporary and geological distribution of the genus is briefly reviewed.The variety of the habit of the genus, the recapitulatory features of the seedlings, and the common morphological features are referred to.An attempt is made to formulate a phylogenetic classification, based on the relationships of the flower‐groups in the inflorescence as the first principle of division, on the relationships of the flowers in the flower‐groups as the second principle of division, and on the foliar character as the third principle of division. The theoretical considerations underlying this scheme are presented, together with some already‐known phenomena of the genus which support it. The scheme explains the occurrence of difficulties experienced in placing species in existing classifications.There is given a list of species selected for ex

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1933.tb00385.x

出版商:Blackwell Publishing Ltd    

年代:1933

数据来源: WILEY

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1933.tb00386.x

出版商:Blackwell Publishing Ltd    

年代:1933

数据来源: WILEY

摘要:

SUMMARYIn a discussion of the phylogeny of the subgenusOnagraof the genusOenothera,based on genetical, morphological, cytological, and systematic results, it is indicated thatOnagrawas derived from the large‐flowered subgenusRaimannia,probably in Central America, and that from this ancestry the small‐flowered North American species were produced, through a series of dominant mutations, as the genus spread out and moved northwards following the retreat of the ice. The evidence for these conclusions is derived from (1) the present distribution of the small‐flowered forms in America, (2) the conclusion that e.g.0. Tracyiis derived fromO. grandifloraandO. purpuratafromO. Hookeri,(3) the fact that occasional small‐flowered mutations appear, e.g.de Vriesiiandbienniformisfrom0. Lamarckiana,(4) the fact that0. novae‐scotiaeis composed of two complexes,grandiflorensandparviflorens,the former having petals much larger than the phenotype of the species.Interspecific crossing has played an important part in the development of the subgenus, as a result of which most of the species are permanent crypthybrids, composed of two complexes and breeding true because of catenation or linkage of their chromosomes during meiosis. Thus the species with smallest flowers occur generally in the higher latitudes and usually show catenation of all their fourteen chromosomes into a closed ring. It has been shown experimentally that catenation can arise by crossing two homozygous species ofOenotheraeach having seven free pairs of chromosomes. Probably the hybrid vigour resulting from the heterozygous (heterogamous) condition leads to the survival and spread of such species, while the relatively homozygous derivatives which will occasionally arise through chromatin rearrangement in meiosis combined with inbreeding will be less likely to survive in the struggle for existence. This accounts for the fact that nearly all the small‐flowered species show complete catenation.Following the twin‐hybrid results of de Vries, Renner and others have shown by extensive crossing experiments that mostOenotheraspecies, including all which exhibit a high degree of catenation, are composed of two complexes, the phenotypic equivalents of which are often very different from the phenotype of the species.The conception of parallel mutations in the subgenus is important, because of the evidence that dominant mutations giving rise to smaller flowers have appeared independently and successively in different parts of the continent from different lines of descent. The species and varieties with cruciate petals constitute another series of independent parallel mutations.The large amount of specialization and adaptation in some species ofOenotheracan only be adequately accounted for by the accumulation of small germinal changes (mutations), many of which must have taken place to account for the amount of specific differentiation which appears in the genus. That genemutations occur is known from the existence of such Mendelian mutants asbrevistylis, rvhricalyxand the various dwarf types.Interchange of segments between non‐homologous (heterogamous) species, called by Lotsy internal hybridization or intra‐syngamic evolution, will account for the appearance of a certain number of new types, especially those which are more nearly homozygous than the parent form; but so far as known these usually fail to survive in competition with the more heterozygous, and hence more vigorous, species from which they are derived. For these and other reasons the value of segmental interchange as an evolutionary factor is limited in comparison with the importance of interspecific crossing. Such crossing probably took place on a large scale in the early evolution of the group, producing a swarm of crypthybrids with a high degree of chromosome catenation, which were successful in spreading on account of their hybrid vigour. Gene mutations occurring regularly throughout this swarm are sufficient to account for the further differentiation of species which has taken place, segmental interchange of chromosomes playing a minor role in the same forms.Two new species are described, and the recognized species of subgenusOnagraare listed, with their type‐localities, petal length, and indications of their relationships and chief differences. The complexes and chromosome catenation are also given in those species in which it has been worked out, and references are made to various studies of naturalized hybrid populations in Europe.The expenses connected with the cultivation of many species and their hybrids have been defrayed in part by grants from the Royal Society. Other faculties have been provided in Re

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1933.tb00387.x

出版商:Blackwell Publishing Ltd    

年代:1933

数据来源: WILEY

摘要:

SUMMARYThe typical dichlamydeous cyclic Dicotyledon is so organised that the petaloid character of the corolla can be regarded as a function of a certain combination of conditions as regards time and space: time, in so far that the petaloid feature occurs at a definite stage in the series of developmental processes, following, as it does, upon the differentiation of a (usually) uncoloured (i.e. green) calyx; space, in that it is exhibited on the set of radii alternating with the radii of the sepals. Penetrating a little below the surface appearance, we find we can express these same relations in terms of the vascular anatomy as follows. Those floral members (again taking the typical case) which receive as midribs the first set of equidistant bundles to leave the central cylinder show sepaloid characters; those similarly receiving as midrib bundles the outgoing strands on the alternate set of radii exhibit petaloid colouring.It is found that the marginal veins of the sepals of such Dicotyledon types arise in two different ways, less frequently as true lateral veins from the midribs, more often either through the detachment from the central cylinder on the alternate radii of trunk cords which dissociate in due course into a petal midrib and twin bundles which enter the adjacent side of the sepal to right and left, respectively, and become the marginal vein of that side; or through the departure of pairs of separate strands within the limits of the corresponding alternate sectors.In typical monochlamydeous cyclic Dicotyledons radial organisation follows the same scheme as in dichlamydeous types, notwithstanding that the perianth here takes the form of a single whorl of structures. Such monochlamydeous types may be divided into two classes. In the one class only the issuing vascular bundles on the corresponding set of radii enter the perianth members. These bundles become the midribs. They may give off lateral veins at any point or may remain unbranched.In either case the individual member is homologous with the individual sepal and is typically green.In the other class each member receives not only the bundle on its own radius but also half the perianth component proper to the alternate radius on each side, either as separate strands or (in gamophyllous types) as undisjoined components of perianth‐stamen trunk cords. The first‐mentioned bundle becomes the midrib of the tepal, the two others become marginal veins, the one entering the tepal on the right, the other that on the left.In forms belonging to this class the tepals are typically petaloid. Each may be regarded as the counterpart of one sepal of dichlamydeous types + half the neighbouring petal on either side.This equivalence is not infrequently indicated outwardly by the considerable thickness of the tepal members as compared with that of the sepals and petals of the nearest allied dichlamydeous forms.The accompanying drawings were made by Miss D. F. M. Pertz, to whom I desire to express my grateful tha

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1933.tb00388.x

出版商:Blackwell Publishing Ltd    

年代:1933

数据来源: WILEY

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1933.tb00389.x

出版商:Blackwell Publishing Ltd    

年代:1933

数据来源: WILEY