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

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

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P]. 3. p] 4. Umkomasiaceae (= Corystospermaceae) [genera: Umkomasia, Pilophorosperma, Nidia, Pteruchus, Nidistrobus, Dicroidium, Rhexoxylon satellite genera Rhaphidopteris, Pachypteris, Pteroma, Ptilozamites, Harrisiothecium]. 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.

However, Takhtajan (1953) retains Sahni 's nomenclature and Lam (1950) extends the distinction even to the angiosperms. Nevertheless the acceptance of Chamberlain's nomenclature for the two di vi sons of gymnosperms is, not against Sahni 's recognition of the two main phy\etic lines in this group; only the basis of their distinction is different. Another feature of Sahni 's classification, which seems to have come to stay, is the 37 separation of Taxus and its allied forms from the Coniferales and their inclusion in a new order, Taxales.

Stamnostoma huttonense. A, seed in longisection. B-E, successive transections at levels indicated by b-e in A. (all after Long, 1960b). 2. 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.

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