By Pant, D.D. and Osborne, R. and Birbal Sahni Institute of Palaeobotany
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Extra info for An introduction to gymnosperms, cycas, and cycadales
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.
Meyen admits that Ginkgo and cycads have platyspermic as well as radiospermic seeds and yet he prefers to treat the seed plants as representing continuations of two distinct lines of Devonian seeds. Paradoxically enough he puts seed plants beginning with two kinds of seeds and some of their groups having both kinds under three classes whose relationships with one another remain unspecified. A synopsis of Meyen's classification is given below:Division - Pinophyta (= Gymnospermae) Class Ginkgopsida Order 1.
Chamberlain (1920, 1935), on the contrary, emphasizes mainly the factual details of the differences in habit, stem anatomy and leaves of the two groups. The names chosen by Chamberlain are also noncommittal. , Amold (1948), Engler et al. (1954) and Pant (1957) have preferred Chamberlain's names. 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.