摘要:

The phyletic position of the MacaronesianRanunculusspeciesR. cortusifoliuswas investigated in an analysis of meiotic metaphase I in a series of interspecific hybrids (eight diploid species, nine genome combinations, 25 F1‘s). The exceptionally large size of theR. cortusifoliuschromosomes, previously described via cytophotometry, was confirmed and allowed a positive identification of the constituent haploid chromosome sets in all hybrid meiotic preparations studied. MI was largely univalent‐unpaired, with 0 to average 1–2 bivalent‐chiasmate pairs (2n= 16), sporadic non‐bivalent sticky groupings and occasional (two hybrids) loose segmental associations (figured). The comparative study of the univalent‐bivalent meiotic profiles for the various genome combinations showed that theR. cortusifoliusgenome has diverged almost as widely from the genomes of species in its own taxonomic group (sect.PterocarpaOvcz.) as it has from those of certain morphologically diverse, progressive species from two other sections (sect.Xiphocoma, sect.Ranunculus). The morphological conservatism ofR. cortusifoliusin the face of wide genetic divergence is discussed; an explanation invoking as its most important single cause excessive genome size, on a pre‐adaptive model (Waddington&Lewontin)

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1976.tb01357.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

The striking diversification of leaf shape in juveniles of the hybrids betweenParsonsia heterophyllaA. Cunn. andP. capsularis(Forst. f.) R. Br. is described and illustrated. The applicability of Turing's diffusion reaction theory of morphogenesis was tested, and it was found that the diversity could be explained as a result of interactions between sine‐wave‐like gradients of morphogens in the leaf primordia. Precession in the onset of sexual maturity leads to the fixation of juvenile leaf characters. This neotenic process combined with natural selection may then lead to speciation and adaptive radiation, as in the AustralianParsonsiaspp. The operation of these processes in other New Zealand genera and in Australian Proteaceae is discussed in relation to adaptive radiation and evolut

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1976.tb01358.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

A breeding programme using Jamaican species ofColumneademonstrated that a majority are interfertile, and made possible the synthesis of artificial hybrids betweenC. urbaniiStearn andC. rutilansSwartz resembling wild plants previously suspected to be of hybrid origin.Evidence is provided to show that species in sect.Columneaare interfertile with species in sect.Pterygoloma.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1976.tb01359.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Sherk's cytogenetic findings are outlined, as far as they relate to the possible hybrid origin ofColumnea quercetiOersted. Morphological evidence is provided to show that a hybrid origin is not impossible because there is a precedent for natural hybridization within the genus.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1976.tb01360.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Hyparrhenia involucrata Stapf is an annual with diploid, aneuploíd, tetraploid and hexaploid chromosome races on a base ofx= 10, whilst M.subplumosaStapf is known to be tetraploid and perennial. The two species overlap considerably in their vegetative and floral attributes. Whilst the floral characteristics (such as number of awns and sex of imperfect flowers) are fairly constant withinH. involucrata, they are quite variable in H.subplumosa: the evolutionary significance of some of these variations is discussed. Some of the observations on size, variability and fertility of pollen grains are interpreted using data from chromosome numbers and meiotic behaviour. Preliminary observations on the hybrids between a diploid race ofH. involucrataandH. subplumosaindicate that the genomes of the two species are highly homologous and that perennial habit is a dominant trait controlled by a single gene

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1976.tb01361.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

An analysis of the present composition of the Josani Forest, Zanzibar is discussed and the status of the forest considered. Particular interest is paid to those species used as food plants by the endemic subspecies of red colobus monkey,Colobus badius kivkiGray.The forest is shown to haveCalophyllum inophyllumL. and a species ofEugeniaas co‐dominants. The former species is considered likely to be indigenous to Josani, not introduced as presumed by previous authors. A number of species in Josani are found widely distributed on islands in the Indian Ocean, and the relation of Josani Forest to these insular floras is discussed.It is tentatively suggested that the forest lies partially in a mature solution basin and that this has had an important influence on the present composition of the fores

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1976.tb01362.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY