摘要:

The epiphytic orchids of 31 sites in Eastern, Midwestern, Western and Northern Nigeria are enumerated. The distribution of these 109 species of orchids is related to geographic location and to the environmental factors: climate, vegetation type, most common tree species. Distribution is further discussed in relation to variation within species. An hypothesis of a former more or less continuous orchid population fragmented by climatic shifts toward dryness, by erosion and land level sinkage, and by change of vegetation brought about by man, is advanced. It is suggested that, with such fragmentation, the orchids are now in a phase of rapid speciation and evolutionary development.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1969.tb00120.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

The date distribution of emergence in panicles ofDactylis glomeratawas studied over several years at the Welsh Plant Breeding Station, Aberystwyth. Indigenous populations from southwest England, and western France showed a negatively skew distribution, as did cultivars from U.S.A., Denmark, and New Zealand, but in those from U.S.S.R. the skewness was not significant. It is suggested that this negative skewness could have arisen as a selective response to light intensity. This could explain why the predominant growth forms in the species' natural habitat are of the taller ‘hay’ type. The method of growing seed commercially in drilled rows over many generations has eliminated the prostrate forms. The latter have survived in old pastures but never predominate, and may be greatly reduced should the intensity of grazing be increased and prolonged. Self regeneration by ‘own’ seed in sward plants is hindered by ‘Choke’ disease(Epichloe typhina)which inhibits and can prevent panicle emergence so that in extreme cases plants become vegetative and non‐sexual.There seems to be no inherent physiological barrier to late heading, but it has not, so far, been possible to assemble a population of agronomically suitable late‐flowering plants. For this reason breeders have not been able to produce cultivars of cock's‐foot comparable with the late‐heading, leafy, grazing varieties develop

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1969.tb00121.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

A new genus and species of arctolepid arthrodire,Qataraspis deprofundisis based on an anterolateral plate recovered from a bore‐hole in Qatar, Persian Gulf at a depth of nearly two and a half miles. It is compared with the corresponding plates of all known arctolepid arthrodires, particularly those referred to the undefined genusKujdanoteiaspisStensiö.The British speciesK. anglicais described in detail and referred to a new genus,Heightington‐aspis,and a specimen from the Senni Beds of the Black Mountains is described asAiluracantha dorsifelisgen. et sp.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1969.tb00122.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

The two medieval species concepts, the essentialist and the nominalist, have been replaced by the biological species concept, denned in terms of the relation (i.e. ‘reproductively isolated’) between populations. The species represents an important level in the hierarchy of biological entities from the molecule to the community. Six major areas are discussed, on which much of the research on species is now focu

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1969.tb00123.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

There are some fundamental reasons for the current lack of success in exploiting the sensitivity and precision of the computer for group‐forming. Serious informational distortions have been found for a number of widely used grouping systems. There has been a neglect of the need for special treatment of certain kinds of data before and during group‐forming. Some such treatments are described for use with the generally distortion‐free Relative Heterogeneity Functions. Some of the items being grouped may have significant internal variation for certain properties. A method is offered where grouping can proceed using data representing the distributions of these properties, giving a better result than using their average values. A way is given for extracting overall size variation from a set of measurement properties. The important matter of some properties being homologically indistinct is raised. It is concluded that it is essential to reduce the contribution of each of these properties to the overall similarity measure, and a way of doing this is described. The resulting system gives an essentially non‐Adansonian t

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1969.tb00124.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY