摘要:

This account of chromosome variation in the Commelinaceae is based both on the authors' personal experience with a very large living collection of the family at Kew, and on the numerous reports of earlier workers. There can be few families showing such a wide range of chromosome numbers, karyotype morphology and meiotic behaviour, the description of which may be of interest to cytologists, evolutionists and taxonomists alike. In this present survey the information is presented within the framework of a tentative classification of genera proposed by Brenan, and comments are made throughout on the relevance of cytology to his taxonomic treatment of the family. It is hoped that this account will foster further interest in the Commelinaceae, and in particular, encourage more thorough appraisal of intraspecific chromosome variation and interspecific homologies.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1972.tb00929.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

The structure of the carpel has been studied in flowers of the Neodregeae (DipidaxandNeodregea). Except inD. triquetra, which is syncarpous, the carpels are united below and free above. A dorsal bundle, two or more lateral bundles, and two placental bundles supply each multiovulate carpel. The six placental bundles of the tricarpellate pistil are united by twos in the lower part of the pistil, forming three opposite compound placental bundles in most species ofDipidaxand three alternate bundles inD. triquetraandNeodregea: In the latter, an additional septal bundle continues upward as a branch from the compound placental bundle. Sutural openings are usually short and restricted to the top of the locule. All the Neodregeae have monotegmic ovules.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1972.tb00930.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

In an earlier paper, which includes pollen descriptions for 93 genera and approximately 430 species of the large tropical family Annonaceae, the author laid the foundation for a generic reclassification and natural phylogeny of the family based largely on comparative palynology. The present paper includes generic pollen descriptions for an additional 12 genera and 18 species of Annonaceae.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1972.tb00931.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

The morphology and anatomy ofSynsepalum dulcificumhas been described, principally because of enquiries from pharmaceutical industries considering this species as a potential replacement of the sweetening agent cyclamate. With the aid of a stereoscan and the light microscope, the pollen grains have been studied for the first time. The grains have either three, four or five colpi. The exine has two well‐defined layers. The scanning electron microscope has revealed a very fine striate‐granular pattern on the sexine. The importance of leaf venation in the classification of the Sapotaceae has been emphasized in a detailed description ofSynsepalum dulcificum: The need for further studies has been no

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1972.tb00932.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Antheridia and archegonia ofMnium hornumare produced according to an endogenous rhythm that approximates to an annual cycle. Short days appear to have a delaying effect on gametangial production, but continuous exposure to 7.25‐hour days at both 10° and 20°C is incapable of causing complete suppression. The cycle shows some tendency to precede spring conditions and it is suggested that the effect of short days in winter is to preserve its co‐ordination with the seasons.Archegonial induction inM. undulatumtakes place in response to long day treatment, although an alternative stimulus can be provided by a rise in temperature, the critical day length being between 7.25 and 12 hours at 10° C. MaleM. undulatumis also a long day plant, but a diurnal fluctuation in temperature is essential to inflorescence production. Temperature ranges of 5.5°‐11° C and 10°‐20°C are suitable for antheridial induction i

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1972.tb00933.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

Sporophytes from natural populations ofThelypteris palustrisandOnoclea sensibiliswere subjected to breeding tests to reveal the presence of recessive lethal alleles in their genotypes. All sporophytes were found to be heterozygous for recessive sporophytic lethals. Despite the capability for producing completely homozygous genotypes by intragametophytic self‐fertilization, ferns in natural populations seem to retain considerable genetic loads of deleterious recessive alleles. It is suggested that natural selection operates to strongly favour heterozygous rather than homozygous sporophytes under most condition

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1972.tb00934.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1972.tb00935.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY