摘要:

SUMMARYA light and electron microscope investigation of the tapetum during stages in the ontogeny of a variety of gymnospermous ovules reveals that eventually this tissue degenerates and forms a thick acetolysis‐resistant membrane (the tapetal membrane) between the embryo sac and the nucellus. This membrane is not considered part of the megaspore membrane in the sense that that term is used in free‐sporing heterosporous plants.In the mature ovules of the genera investigated the true megaspore membrane is present as a thin, acetolysis‐proof membrane closely associated with the peripheral prothallial cells and internal to the thicker tapetal membrane. This megaspore membrane can be related to a somewhat more elaborate structure that is present at the earlier stages of development.There is strong evidence to suggest that the events in the tapetum of the ovule are to some extent paralleled in the tapetum of the polle

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1966.tb00061.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

SUMMARYThe development of stomata and other interesting anatomical features of leaves, sheathing stipules and perianth lobes of 5 species ofMagnoliaand 4 species ofMicheliawere studied.Very often the mature foliar stomata are paracytic with 2 parallel subsidiaries and 1 or more parallel encircling cells but the stomata in the sheathing stipules and perianth lobes are usually anomocytic. A fairly constant feature of the foliar stomata of these plants is the partial overlapping of the subsidiary cells by the guard cells.Epidermal cells of a few species contain calcium oxalate druses. InMagnolia grandifloraandM. pumilathe epidermal cells possess peculiar rod‐shaped bodies of uncertain chemical nature.Polygonal or lobed thick walled brachysclereids occur singly or in groups in the various investigated species. Thin walled vesiculose sclereids are found in the leaves of all plants but they are absent in other organs of some species.The 2 parallel subsidiary cells and encircling cells of stomata develop from the same initial. The development of stomata is, therefore, typically mesogenous (syndetocheilic). According to Rao (1939) the encircling cells in some of these plants are formed by divisions of the subsidiary cells and although this is partly true the encircling cells of a majority of stomata are formed directly from the stomatal meristemoids.According to Paliwal&Bhandari (1962) the anomocytic stomata of the perianth lobes ofMagnolia grandiflora, M. stellataandMichelia champacaare haplocheilic which implies that they are perigenous. However, we find that the irregular ring of cells around the guard cells of stomata in these parts and in the sheathing stipules, develop as a result of divisions in the mesogene subsidiary cells indicating thereby that these stomata are mesogenous and their development is essentially similar to that of foliar stomat

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1966.tb00062.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

SUMMARYProgress in a long‐term experiment designed to re‐create the Tuberosum Group of potatoes by selection from the Andigena Group is described. Both mass selection and pedigree methods are being used and current populations (5 years, 2 generations removed from South American sources) are estimated to be about half way from one Group to the other. Semi‐natural selection for tolerance of long days results in earlier and heavier cropping and in certain correlated changes constituting the day‐length syndrome; there has also been considerable response to natural selection for blight resistance, this selection having been advanced by growing sub‐populations annually under heavy natural attack in Cornwall. It is concluded that the Tuberosum Group evolved under (semi‐) natural selection for long‐day tolerance and blight‐resistance, supplemented by artificial (i.e. conscious, human) selection for tuber shape, size and colou

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1966.tb00063.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1966.tb00064.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1966.tb00065.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1966.tb00066.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

SUMMARYChromosome counts have been made and the karyotypes illustrated for species ofBolbitis, TeratophyUum, LomagrammaandLomariopsis, all included within the subfamily Lomariopsidoideae for which 6 out of the 7 genera contained in the subfamily have now been sampled. With the sole exception of African species ofLomariopsisall are uniformly based on a monoploid of w=41. The 4 African species investigated are all anomalous, having chromosome numbers conspicuously less than 41. The suggestion is made that at least some of these numbers imply chromosome reduction perhaps through fusion from a previously more normal condition. The nature of desirable further evidence is indicated.

ISSN:0368-2927    

DOI:10.1111/j.1095-8339.1966.tb00067.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY