An introduction to gymnosperms, cycas, and cycadales by Pant, D.D. and Osborne, R. and Birbal Sahni Institute of PDF

By Pant, D.D. and Osborne, R. and Birbal Sahni Institute of Palaeobotany

ISBN-10: 8186382011

ISBN-13: 9788186382011

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By Pant, D.D. and Osborne, R. and Birbal Sahni Institute of Palaeobotany

ISBN-10: 8186382011

ISBN-13: 9788186382011

Show description

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Extra info for An introduction to gymnosperms, cycas, and cycadales

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CADALES s 0 Later the megasporangium and the sterile appendage became laterally recurved on the stalk so that the megasporangium became placed between the stalk and the sterile lobe. Now the stalk and the sterile lobe extended around the megasporangium and their margins fused to form the integument (Pant, 1966). Thus interpreted, the single tapering horn of the seed of Buriadia represents the free apical part of the sterile segment (telome) and the truncated horn represents the free part of the stalk formed by a me some (Fig.

ORIGIN AND EVOLUTION OF SEEDS AND CUPULES In the seeds of pteridosperms usually more than two sterile branches (telomes) seem to have given rise not only to the integuments but also to the cupules. The integument of the seed of Cyeadeoidea morieri is divided by radial plates of thick walled cells into four longitudinal chambers like those of Lagenostoma. g. Ceratozamia, Maerozamia, Eneephalurtos is also divided around the micropyle into 7 to 16 lobes. The formation of a star-shaped opening during germination of the seeds of most cycads seems to indicate that the rays of the star are possibly formed between the multiple integumentary lobes or telomes.

Coulter and Chamberlain (1910) were against the use ofthe term since it artificially combined the gymnosperms with the angiosperms although actually the former are somewhat closer to the pteridophytes, from which it separated them. However, Emberger (1944) reintroduced the term Phanerogamae along with a new one, Prephanerogamae, to include the Pteridospermae and Cordaitales which have no embryos in their seeds at the time of shedding. Emberger suggested that the Prephanerogamae shed only megasporangia wrapped in integuments and not true seeds which, according to this author, should also have embryos at that time.

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An introduction to gymnosperms, cycas, and cycadales by Pant, D.D. and Osborne, R. and Birbal Sahni Institute of Palaeobotany


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