摘要:

STOFFBERG, E., 1991. Morphological and ontogenetic studies on southern African podocarps. Shoot apex morphology and ovuliferous cone initiation. Four species ofPodocarpusindigenous to southern Africa were investigated. The morphology of the primordium of the female cone is compared with that of the shoot apex. Rhythmic growth occurs inPodocarpus.The external morphology of bud scales protecting dormant shoot apices is described and illustrated. Female strobili of the three species of sectionPodocarpusstudied are initiated in the axils of euphylls during the spring growth flush as laterally flattened triangular structures. The axillary position of a female cone indicates that it is a modified shoot. The first two cone bracts (prophylls) are formed approximately at right angles to the subtending bract (one or both are fertile), while the 3rd and 4th bracts originate on the anterior and posterior sides of the strobilus respectively. Two to four bracts per cone are formed, not in pairs–the phyllotaxis is spiral. InP.falcatusprimordia of female strobili and vegetative branches could be distinguished only after emergence of the seed scale complex. Based on cell differentiation, well‐defined cytological zones can be distinguished in the shoot apex and it is classified as being of theAbies‐Cryptomeria‐lype.Meristematic zones of cone primordia and vegetative branches are basically similar, although the former are less well defined. No gradual transition from a vegetative to a reproductive apex could be identified and it would seem that the fate of axillary buds are determined at the time of their origination or even

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1991.tb00197.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

STOFFBERG, E., 1991. Morphological and ontogenetic studies on southern African podocarps. Initiation of the seed scale complex and early development of integument, nucellus and epimatium. The primordium of the seed scale complex (ssc) (ovule with epimatium) is initiated in the axil of the first or second cone bracts (prophylls) as a dome shaped structure consisting of a group of uniform, meristematic cells. A distinct protodermal layer develops. The nucellus is a dome on the ventral side of the ssc primordium. In the species of sectionPodocarpusthe integument is initiated as a circular ridge around the nucellus, while inP.falcatustwo protrusions on the anterior and posterior sides of the nucellus are the first indications of integumentary differentiation. The integument of all species studied is of subdermal origin. The epimatium(sensu stricto)is initiated after the integument, is of subdermal origin and forms a hood around the developing ovule. Considering research results, together with related literature, it is concluded that the integument of gymnosperms may be homologous with the outer integument of a bitegmic angiospermous ovule, that the position of integumentary initiation may be specific for certain taxa and that there seems to be no constant sequence of emergence of ovular envelopes in gymnosperms.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1991.tb00198.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

HILL, R. S.&READ, J., 1991. A revised infrageneric classification ofNothofagus(Fagaceae). An examination of cupule morphology, leaf architecture and cuticular morphology ofNothofagusspecies demonstrates that the existing infrageneric classifications are inaccurate. Four subgenera are proposed, based on these characteristics as well as other morphological information. This analysis indicates that the traditional pollen groupings ofNothofagusclosely reflect the infrageneric taxonomy. It is hypothesized that deciduousness is primitive inNothofagus, and the evergreen habit has arisen more than once, and therefore the deciduous or evergreen habit is invalid as a primary taxonomic character.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1991.tb00199.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

HILL, R. S., 1991. TertiaryNothofagus(Fagaceae) macrofossils from Tasmania and Antarctica and their bearing on the evolution of the genus. Eight new species ofNothofagusare described from Tertiary deposits in Tasmania and West Antarctica, based on leaves and cupules. Several other species are re‐examined. The new species include the first fossil species in the subgeneraBrassoporaandNothofaguswith organic preservation, and the first substantial description of fossil reproductive structures. The fossils demonstrate that by the Oligocene most of the evolution within the genus was complete, although there have been changes in leaf morphology since, which are probably directly related to climatic changes. The change in distribution of the subgenera in Australasia during the Tertiary is considered, and temperature changes and catastrophic disturbance are identified as two important factors affecting the distribution ofNothofagu

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1991.tb00200.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1991.tb00197a.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY