Download e-book for kindle: 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

ISBN-10: 8186382011

ISBN-13: 9788186382011

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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. Pant and Mishra (1986) reported a fossil megaspore which showed a miospore enmeshed in its processes and they thought that the processes made such captive microspores readily available for germination in close proximity.

1H), Moresnetia zalesskyi, and Hydraspenna tenuis from Ireland, which are also found permineralized, show a basal vascular strand which gi ves out branches to the integumentary lobes so that each integumentary telome shows a central vascular strand. Carboniferous and Permian seeds Numerous archaic seeds have also been reported from the Carboniferous as well as Permian beds in different parts of the world. The earliest of these occur in the Lower Carboniferous. Some of these later Palaeozoic seeds are radially symmetrical or rounded in cross section (radiospermic) like the Upper Devonian seeds but there are others among them which are flattened in one plane (platyspermic).

CLASSIFICATION Schoute (1925), who first showed that the ovule in Cordaitanthus was attached to a lateral appendage, pointed out that this did not support Sahni's division of the gymnosperms into the Stachyosperms and the Phyllosperms. Since then, Florin's extensi ve work (1938-45, 1951) on the strobili of Cordaitales and conifers has made it-abundantly clear that the ovule in both these groups is borne on a lateral appendage of a short axis. Florin does not precisely state the nature of the ovule bearing organ but the fact that he often refers to it as a megasporophyll suggests that he regards it as a foliar structure.

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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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