New PDF release: An introduction to gymnosperms, cycas, and cycadales

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

ISBN-10: 8186382011

ISBN-13: 9788186382011

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

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Some of these ancient gymnospenns have more or less regular and symmetrical cupules but those of Xenotheca and Moresnetia 2. ORIGIN AND EVOLUTION OF SEEDS AND CUPULES are quite asymmetrical. The asymmetrical cupules of Carboniferous Eurystoma angulare (Fig. 11K) are similar to those of the above mentioned asymmetrical Upper Devonian forms but in these their single seeds become surrounded by a system of rather irregular dichotomising terete branches (Long, 1965). The structures formed are hardly like cupules but are clearly suggesti ve of their beginnings.

3. CLASSIFICATION Order 4. Ginkgoales 1. Ginkgoaceae 2. Karkeniaceae ? 3. Pseudotorelliaceae? Order 5. 1. 2. Leptostrobaceae Iraniaceae ? Order 6. 1. 3. ) Order 4. Cycadeoideales) Bennettitales (= 1. Bennettitaceae (Cycadeoideaceae) 2. Williamsoniaceae Order 5. Gnetales Gnetaceae Order 6. 1. Welwitschiales Welwitschiaceae Class Ephedrales Pinopsida (= C;;oniferopsida) Order 1. ) 2. ) 3. ) Order 2. Buteoxylaceae Trigonocarpales (= Trigonocarpaceae Cordaitanthales 1. Lagenostomales (=Lyginopteridales) Lagenostomaceae Order 2.

9. Lyrasperma scotica. A, B, longisections of seed in minor (subsidiary) and major (principal) planes. C·J, successive transections of seed at levels indicated by c-i in B (all after Long. 1960c). a - archegonium. cc - central column. it integument lobe. la -lagenostome. mm - megaspore membrane. n - nucellus. pc - pollen chamber. pl- pollen. pr - female gametophyte. s - salpinx. se - sclerotesta. vb - vascular bundle. w - wing. which become hooked to the whip-like processes. Chaloner (1967) mentions a Hong Kong Selaginella whose megaspores reportedly carry its microspores enmeshed in their exine processes in a "vulcro-like" attachment so that they can germinate close by.

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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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