. Morphology of gymnosperms. Gymnosperms; Plant morphology. 176 MORPHOLOGY OF GYMNOSPERMS When the numerous detached paleozoic seeds were grouped as radiosperms and platysperms (12, 14), it was supposed that the latter, at least, belonged to the Cordaitales, because such as had been definitely referred to the group were of the more or less flattened type. However, since the discovery that certain of the CycadofiUcales, as Aneimites and Pecopteris Pluckenetii, bore seeds of the platysperm type, it is evident that the ref- erence of any seed to Cycadofilicales or Cordaitales must await the disco

. Morphology of gymnosperms. Gymnosperms; Plant morphology. 176 MORPHOLOGY OF GYMNOSPERMS When the numerous detached paleozoic seeds were grouped as radiosperms and platysperms (12, 14), it was supposed that the latter, at least, belonged to the Cordaitales, because such as had been definitely referred to the group were of the more or less flattened type. However, since the discovery that certain of the CycadofiUcales, as Aneimites and Pecopteris Pluckenetii, bore seeds of the platysperm type, it is evident that the ref- erence of any seed to Cycadofilicales or Cordaitales must await the disco

Central Historic Books / Alamy Stock Photo

Image ID: PG2K7J

This image is a public domain image, which means either that copyright has expired in the image or the copyright holder has waived their copyright. Alamy charges you a fee for access to the high resolution copy of the image.

. Morphology of gymnosperms. Gymnosperms; Plant morphology. 176 MORPHOLOGY OF GYMNOSPERMS When the numerous detached paleozoic seeds were grouped as radiosperms and platysperms (12, 14), it was supposed that the latter, at least, belonged to the Cordaitales, because such as had been definitely referred to the group were of the more or less flattened type. However, since the discovery that certain of the CycadofiUcales, as Aneimites and Pecopteris Pluckenetii, bore seeds of the platysperm type, it is evident that the ref- erence of any seed to Cycadofilicales or Cordaitales must await the discovery of its actual connection. As a result, many de- tached seeds, heretofore referred with con- siderable confidence to Cordaitales, are now in uncertainty; but out of the vast numbers found, many of them must have belonged to this group. Grand 'Eury (17) has called attention to the fact that there are many more seed genera that probably belong to Cordaitales than there are shoot genera (Cordaiies, etc.) to receive them. Among those that seem most certain are those somewhat flattened seeds with heart- shaped base that have been included by Renault in the genus Cordaicarpus (Cardio- carpus of Brongniaet). The testa, derived from a single integument, is diflferentiated into outer fleshy and stony layers. There are two sets of vascular strands: one traversing the outer fleshy layer; the other forming a tracheal plate at the base of the relatively free nucellus, which gives rise to a tracheal mantle in the peripheral region of the nucellus, similar to that in Stephano- spermum, but not so complete (14). The usual nucellar beak is very prominent and projects into the micropyle. The whole structure agrees so closely with that of the ovules described. Fig. 208. •— Cordatan- thus Williamsonii: longi- tudinal section of ovule, showing upper portion of nucellus, lower portion of nucellus free from the in- tegument, cavity which . doubtless contained the female gametophyte, outer int