摘要:

Several distinctive histological features of the stamen, especially of the filament, are described, some of these for the first time: for example, commonness of (a) mesarch xylem maturation, amphicribral bundles or else collateral strands with phloem considerably enveloping the xylem, and clustering of sieve elements of a bundle and their spatial separation from tracheary elements, (b) exclusively helical wall thickenings of tracheary elements and absence of sclerenchyma, (c) open stomata, a weakly developed cuticle, a prominent intercellular‐space system, xylem lacunae, and (d) tannins and crystals. Some of the features in category (a) seem related to the nutritional needs of developing pollen grains in the anther. Features in category (b) are directly related to the usual expansion of the stamen, in particular the filament, before and at anthesis. Features in category (c) (and possibly (d)) probably promote a rapid loss of water or a disruption of the water supply to the anther, and therefore might facilitate anther dehiscence (these features could operate either in isolation or in unison). Tannins, crystals, and secretory structures have been implicated in the protection of pollen against predator

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1976.tb01811.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Lodicules are basically peltate‐ascidiate phyllomes, as are many other perianth appendages in Monocotyledons. Their structure is especially obvious inZeaand several Andropogonoideae and Panicoideae. In various genera of the Panicoideae and inOryzathey are fundamentally ascidiate but longitudinally split on their distal sides. Lodicules of the Festucoideae, with their dorsal wings, are easily derived from the latter, and so are probably at least some bambusoid lodicules. These findings lend support to the classical interpretation of lodicules as discrete perianth appendage

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1976.tb01812.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Interrelationships between OTUs (operational taxonomic units) were assessed through comparisons based on a constant character number, using principal components analysis. This approach results in a uniform treatment of OTUs, despite variations in the number of definite entries for character states that could validly be made. In addition, the risk of distortion of the ordination scatter as a result of a bimodal frequency distribution of the number of characters available for comparisons is minimized. Appropriately applied, the approach also provides indications of the consistency of the features of the ordinations and reveals where more caution in interpretation is advisable.The main analysis divided the OTUs into two unequal‐sized groups, with a few intermediates; these were concluded to be more closely allied to the large than the small group. The significance of these groupings, in terms of their species contents, is discussed in relation to the method and to recent taxonomic treatments of theBulbostylis/Fimbristyliscomplex. Some taxonomic conclusions must be tentative because of the limitations of the sampl

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1976.tb01813.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Pistacia atlantica, P. palaestina, P. lentiscusandP. saportae, were found to have great similarity in their embryology and fruit development. The anatropous, pendulous and crassinucellate ovule was initially unitegmic; later, the integument split close to the micropyle, forming a partial second integument. After anthesis there was a development of a hypostase and an obturator. The development of thePolygonum‐typeembryo sac followed division of a megaspore mother cell, giving a tetrad or triad of megaspores. The functional megaspore was the chalazal one. The ovary developed into a mature pericarp after anthesis, even when pollination was prevented, and before the zygote divided. Therefore, the fruit can be parthenocarpic. The ovule started to grow after initiation of embryo development until it filled the cavity within the pericarp. The zygotes were dormant for 4–18 weeks after pollination. InP. saportaereproduction became arrested during the development of the embryo sac; only very few abnormal embryos were found. No fixed pattern of embryo development could be discerned. The endosperm was initially nuclear, becoming cellular when the embryo started to develop. The seed coat was derived from the integument and the remnants of the nucel

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1976.tb01814.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1976.tb01811a.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY