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 

 integument, inner integu- 

 ment free from the outer 

 integument below but more 

 or less applied to it above, 

 bract, and secondary axis 

 bearing ovule; X 35 . — After 

 Renault (3). 



