By Pant, D.D. and Osborne, R. and Birbal Sahni Institute of Palaeobotany
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Extra resources for An introduction to gymnosperms, cycas, and cycadales
Could we not expect other ~odes of seed evolution in other gymnosperms and particularly the angiosperms of which we do not have many clues so far? A permineralized radially symmetrical seedlike structure Coumia5perma remyi (Fig. 12) described by Galtier and Rowe (1989, 1991) from the Middle Tournasian Lydiennes Formation, Montagne Noire, southern France gi ves some support to these ideas. This seed-like body is quite like the earlier Devonian seed Moresnetia but the prominent beak of its megasporangium is completely filled with parenchyma and altogether lacks a pollen chamber.
Other Carboniferous seeds showing different degrees of fusion in the integumentary lobes are Hydrasperma (Long, 1961, Fig. 5) and Calathospermum (Walton, 1949). In the well known seed, Lagenostoma lomaxi, the integumentary lobes are fused right up to the top (Figs. 6A-G) but a canopy of nine fused chambers of hard tissue filled with soft tissue can still be seen and the soft tissue of each chamber is traversed by a central vascular strand (Fig. 6G). The structure of the seed would thus suggest that the integument is formed from nine fused integumentary lobes.
Meyen (1984, 1986) has suggested a new classification wherein he uses the names Pinophyta for gymnosperms and Magnoliophyta for angiosperms in conformity'with the latest ICBN. In his entirely new scheme of classification of the gymnosperms, as the author himself points out, he has not attempted to lean on any phylogenetic or taxonomic systems that were suggested earlier for the gymnosperms. , Ginkgopsida, Cycadopsida and Pinopsida. Out of the three classes Cycadopsida and Pinopsida had been recognised earlier but the recognition of Ginkgopsida is a novelty.