摘要:

For 200 years prior to the 1938 publication of H. F. Copeland, all authorities (with one exception) classified red algae (Rhodophyta) within Kingdom Plantae or its equivalent. Copeland's reclassification of red algae within Kingdom Protista or Protoctista drew from an alternative tradition, dating to Cohn in 1867, in which red algae were viewed as the earliest or simplest eukaryotes. Analyses of ribosomal RNA (rRNA) sequence data initially favoured Copeland's reclassification. Many more rRNA gene (rDNA) sequences are now available from the eukaryote lineages most closely related to red algae, and based on these data, the hypothesis that red algae and green plants are sister groups cannot be rejected. An increasing body of sequence, intron‐location and functional data from nuclear‐ and mitochondrially encoded proteins likewise supports a sister‐group relationship between red algae and green plants. Submerging Kingdoms Plantae, Animalia and Fungi into Eukarya would provide a more natural framework for the eventual resolution of whether red algae are plants or pro

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1995.tb00463.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

New observations regarding secondary growth and vascular tissues inWelwitschiaare based on roots (used because of the longitudinal orientation of most vascular tissues).Welwitschiahas successive cambia that produce xylem and phloem. Contrary to previous reports, the cambia produce secondary phloem with phloem rays and secondary xylem that has readily definable xylem rays and axial parenchyma. Internal sculpturing (grooves associated with pit apertures) of tracheary elements is figured with SEM; observations confirm the descriptions of Bierhorst (1960). Tori and vesturing are apparently absent on pits of tracheary elements. Abundance of gelatinous secondary walls may be related to water economy to a minor extent. A feature recently reported forEphedrawood is newly reported for xylem rays, phloem rays and conjunctive tissue ofWelwitschia:presence of minute calcium oxalate crystals lining intercellular spaces. This feature is apparently limited to the two genera. The ontogenetic origin of vascular strands added by secondary activity can be traced to phelloderm. In this feature,Welwitschiadiffers fromGnetum,in which the ultimate origin of new cambia can be traced to cortical tissues.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1995.tb00464.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Quantitative and qualitative data are given for the two African species ofGnetum(GnetumsectionGnetumsubsectionMicrognemones). These species are lianoid and lack the fibre‐tracheids ofG. gnemonbut have about the same vessel element and tracheid length as in that species. Vessel diameter is related to stem age and organography. Tori are clearly present in tracheary elements of the AfricanGnetumspecies, a first report for the genus. In these two species, origin of the lateral meristem, which produces vascular tissue and cambia, can be traced directly and indirecdy to cortical parenchyma. A second kind of meristematic action, newly reported forGnetum,is produced by proliferation of axial parenchyma, fragmenting secondary xylem. Both presence of tori and site of origin of lateral meristematic activity inGnetumcontrast with corresponding conditions inWelwitschi

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1995.tb00465.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Seed dispersal ofBiserrula pelecinusvia cattle dung in a semiarid pasture is analysed by quantification of the viable seed content of cattle dung, assessment of the percentage of readily germinable seeds in growth chamber of seeds collected from the plant and from dung, monitoring of the on‐field frequency of the species in dung pats and in surrounding (control) pasture plots the four springs after dung deposition, and quantification of the pasture area occupied by dung pats. Large amounts of seeds of the species are dispersed by cattle (up to 4 seeds g‐1of dry manure in June 1991), and the germinability of the seeds increases significantly following their passage through the cattle gut (from 2.5% to 9.5%). In the first three springs after deposition, the frequency of adult plant of the species on dung almost tripled that found in the surrounding pasture. The effect on the pasture is scale‐dependent and varies considerably between zones depending on the area covered by dung. Thus, presence on dung may explain an average of 8% of the frequency of the species in the pasture at a 10 times 10 cm scale, and up to 20% in some areas. The results are the first evidence of a herbaceous species being greatly favoured in a plant community by its dispersal through herbivore dung, a process that may have profound implications for the interpretation of plant‐herbivore relations and on the evolution of plant

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1995.tb00466.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The structure, distribution and taxonomic importance of foliar stomata in 45 taxa belonging to 19 genera have been studied. In all, six stomatal types have been recognized viz., anomocytic, anisocytic, diacytic, paracytic, hemiparacytic and brachyparacytic. The majority of the taxa are amphistomatic whereas hypostomatic leaves are confined to only three taxa. Stomatal diversity is common but most of the taxa show either dominance or codominance. Stomatal distribution is helpful in distinguishing the three tribes of the Amaranthaceae. The tribe Celosieae shows exclusive presence of anomocytic and anisocytic stomata whereas Amarantheae and Gomphreneae show other stomatal types viz., paracytic and diacytic in addition to anomocytic and anisocytic stomata. Further, the latter two tribes are each distinguishable into two subtribes on the basis of stomata.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1995.tb00467.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY