摘要:

DRANSFIELD, J.&MOGEA, J. P., 1984. The flowering behaviour ofArenga(Palmae: Caryotoideae). The palm genusArmga, with 21 species, displays remarkable variation in flowering behaviour, involving both pleonanthy and hapaxanthy with basipetal production of inflorescences; inflorescences may be bisexual or unisexual, solitary or multiple. The ecological significance of the variation remains obscure and it is still not possible to indicate whether or notArengais primitively hapaxanthic.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1984.tb01561.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

DUCKETT, J. G.&PANG, W. C., 1984. The origins of heterospory: a comparative study of sexual behaviour in the fernPlatyzoma microphyllumR.Br. andEquisetum giganteurnL. ‘The heterosporous fernPlatyzoma microphyllumhas exosporic photosynthetic gametophytes. Those from the small spores are filamentous, with few rhizoids and produce antheridia alone. The gametophytes from the large spores comprise a massive base bearing numerous rhizoids and an upright spathulate lobe of tissue one cell thick. They initially produce archegonia near the base but subsequently develop antheridia on the lobe. Adventitious outgrowths are produced after prolonged culture. These secondary individuals vary from branched filaments bearing numerous antheridia to spathulate lobes with archegonia near the base. Gametophyte sexuality determined during sporogenesis can be modified by subculturing gametophyte fragments. When isolated, portions of gametophytes from both kinds of spores produce adventitious individuals bearing antheridia or archegonia. The proportions of these secondary male and female outgrowths vary according to the nature of the fragment rather than the kind of spore from which the material was derived.The sexual behaviour ofEquiseturn giganteurnfollows the same pattern as in other species ofEquisetumsubgenusHippochaete. Male and female secondary gametophytes may be derived from initially male or female individuals as a result of lamellar proliferation both on intact gametophytes and on subcultures derived from excised lamellae. The antheridia ofE. giganteurnare indistinguishable from those of other species of the subgenus but the larnellae and archegonia are distinct for each speries. Detectable genetir load is absent in bothEquisetumandPlafyzomo.On the basis of the striking similarities in the sexual behaviour ofEquisetumandPlafyzomait is suggested that a crucial step in the development of heterospory is an intimate association between gametophyte morphogenesis and sex organ formation. Gametophyte dioecism and dimorphism resulting from this association may have preceded heterospory in evolutio

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1984.tb01562.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

EDWARDS, D.&ROSE, V. 1984. Cuticles ofNematothallus:a further enigma. Cuticles ofNematothallusLangscnsuEdwards are described from a Lower Devonian (Ditton) exposure on the M50 motorway (Hereford and Worcester, England). Some bear highly distinctive cuticular thickenings sometimes surrounding perforations. The affinities of the cuticles, and the development and possible functions of the perforations are considered.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1984.tb01563.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

HUGHES, N. F., 1984. Cretaceous plant taxonomy and angiosperm ancestors: sources of difficulty. It is suggested that one of the primary reasons for slow progress in identifying angiosperm ancestors is restriction of investigation resulting from inappropriate and unimaginative taxonomic handling of the now much‐extended available data. Because of the incomplete nature of any palynologic evidence, identification of ancestors from it can only come from a very large number of observations of fossils and from strict application of stratigraphic sequence information; quick solutions are most unlikely. The removal of any Mesozoic gymnosperm group from the list of ancestor candidates should only arise from prolonged investigatio

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1984.tb01564.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

KOVACH, W. L.&DILCHER, D. L., 1984. Dispersed cuticles from the Eocene of North America. Macerations of organic‐rich clay from the Claiborne Formation (Middle Eocene) of Tennessee have yielded a wide variety of well‐preserved dispersed cuticles. Details of the epidermal cell patterns, arrangement of the stomata1 complex, trichomes and trichome attachment have made possible the association of some dispersed cuticles with leaf types known from this formation which have similar cuticle, and with modern families. All dispersed cuticles are classified in a morphologic system. Through both our own work and a review of previous investigations we have found that distinct dispersed cuticle types can be recognized and may be used biostratigraphically to characterize geologic strata, palaeo‐ecologically to provide insights into environmental reconstruction, and systematically to follow the history of certain

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1984.tb01565.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

RAVEN, J. A., 1984. Physiological correlates of the morphology of early vascular plants. The early evolution of vascular land plants is considered in relation to the physiological problems of life on land. The universal characteristics of vascular plants (xylem, cuticle, stomata, intercellular air spaces, long‐distance symplastic transport and alternation of generations) are discussed in terms of the essential properties of a homoiohydric phototroph. Likely precursors of vascular plants, and the physico‐chemical and biotic environment in which they occurred, are outlined prior to a discussion of the selective forces acting on the evolution of vascular plants in the Upper Silurian and Lower Devonian. Emphasis is placed on biochemical and structural ‘pre‐adaptations’ which may have occurred in the precursors of vascular plants and on which natural selection could have acted with lignified xylem, stomata, etc., as the end‐products. Guiding principles in the analysis include the physiology of extant plants, physico‐chemical constraints, and compatibility with the fossil record. It is concluded that the likely sequence of acquisition of vascular plant characteristics was: heteromorphic alternation of generations with an erect sporophyte; cuticularization of sporophyte; evolution of xylem; occurrence of intercellular air spaces with pores in the epidermis; stomatal activity of the pores. Endodermis and phloem‐type long‐distance transport probably originated arou

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1984.tb01566.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SICEE, D. C., 1984. Some observations on the structure, cation content and possible evolutionary status of dinoflagellate chromosomes. Dinoflagellate chromosomes have a well‐ordered structure, as observed in living cells, glutaraldehyde/osmium tetroxide‐fixed cells, ultrathin cryosections and freeze‐etch preparations. It is suggested that the stabilization of this chromatin in the living cell is largely mediated by divalent cations, acting as bridging molecules between the DNA superstructure and the protein matrix. Studies using X‐ray micro‐analysis and autoradiography have shown that these chromosomes have high levels of bound Ca and transition metals, and that these are associated with both the DNA and surrounding proteins.The organization and stabilization of chromatin in dinoflagellate chromosomes is quite different from that of the cells of other eukaryotes, but shows some resemblance to the dispersed chromatin of bacteria. The evolution of dinoflagellate chromosomes from a prokaryote‐like ancestral genome is attributed to two main factors–the retention of a primitive cationic non‐histone stabilization system, and a pronounced evolutionary trend towards high DNA values. On this theory, dinoflagellate chromosomes are phylogenetically distinct from all other eukaryote chromosomes, and provide a separate evolutionary route for the attainment of high DNA levels and incr

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1984.tb01567.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

STEBBINS, G. L., 1984. Mosaic evolution, mosaic selection and angiosperm phylogeny. Mosaic evolution is a general pattern of evolutionary change, and is expected on the hypothesis that rvolution is basically opportunistic rather than determinate. It is most often exemplified by constancy with respect to one set of characters over a given period of time, accompanied by more or less rapid change with respect to other characteristics of the same organisms. To the extent that the characters involved are functional and adaptive, mosaic evolution must be guided by mosaic selection. A survey of character differences between species belonging to 59 of the largest genera found in the California flora indicates that mosaic selection has played an important role in the evolution of modern species of angiosperms. Mosaic evolution has also taken place with respect to dinerent chromosomal and biochemical characteristics, as is evident from comparisons between morphological, chromosomal and biochemical differences. When the widespread Occurrence of mosaic evolution and of mosaic selection are recognized, two general principles emerge: the primitive or advanced nature of individual character states cannot be deduced solely on the basis of their correlation or association with other character states which are believed to be primitive or advanced; mosaic selection provides a strong basis for the conclusion that natural selection is the most basic process that converts changing population‐environment interactions into evolutionary chang

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1984.tb01568.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1984.tb01561a.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY