摘要:

The genusTaraxacumis readily divided into “primitive” and “advanced” forms, on morphological and cytological criteria. It is thought that the genus arose in the west Himalayas during the Cretaceous and that apomixis arose at an early stage by means of polyploidy, precocious embryony and asynapsis in the female meiosis. Advances of sexual primitive types and “precursor” types west into Europe were paralleled by the spread of arctic‐alpine types into many regions of the world. During the Pleistocene the precursor types are thought to have generated the widespread advanced sectionCeratophora, which gave rise to many of the advanced species after the last glacial period by hybridizing with primitive and precursor sexuals, thus “fixing” a hybrid

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1973.tb02169.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

The pistil ofColchicumis syncarpous, the carpels having open sutures or well‐marked commissures and many bitegmic ovules of variable orientation. Although the vascularization of the carpel is also variable, there are usually three dorsal bundles and three alternate, septal bundles at the base of the pistil, with occasionally some placental bundles at that level. More often the placental bundles, differentiating basipetally, appear to establish connections with the septal bundles higher up, at the lowermost ovular insertion level. The septal bundles divide in two more frequently in pistils in which the carpellary suture is open than in those in which it is close

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1973.tb02170.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

Anatomical features of seeds ofProsopis farcata(Banks&Solander) Eig, collected at nine localities from various geographical regions and habitats in Israel, were studied. The seeds differ in size, shape and colour, and also in the cracking ability of the surface layer and whether the palisade layer peels off from the rest of the testa upon imbibition or not.The gum extruded during imbibition is formed in gum cavities extending from the endosperm throughout the testa up to the palisades.Water penetration is apparently barred by the outermost wall layers of the external cells of the testa (palisade caps).

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1973.tb02171.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

The scanning electron microscope is used to examine epidermal preparations belonging to three species ofGibasis, a genus allied toTradescantia.The surface topography of the leaf is exposed for investigation at high magnifications, the observations add new information about structural projections from the surface and contribute to an understanding of silica deposition and its organization. Hairs of three main types occur: (1) short two‐celled trichomes, hook or prickle hairs, (2) long uniseriate hairs consisting of four to six cells, (3) three‐celled glandular micro‐hairs. The arrangement and shape of epidermal cells and stomata are reported. Epidermal papillae were observed for the first time in two of the three species; their morphology is described in detail and their spacing expressed mathematically. Variations in the structure and distribution of silica cells are depicted, and new aspects of the silica bodies are displayed in relief. The taxonomic significance of these anatomical characters is discussed in relation to species and chromosome nu

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1973.tb02172.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

The detailed morphology and anatomy of leaves ofBersama abyssinicacollected in Kenya and Uganda is described. Certain differences are noted between the leaves of subsp.abyssinicaand subsp.paullinioidesand the significance of these is discussed. It is suggested that palisade ratio values might be a possible means of differentiating between the two subspecies.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1973.tb02173.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY