XXXV] CABDIOCABPALES 333 



closely than the seeds of the Trigonocarpales, with those of recent 

 Cycads. The nucellus is free laterally from the integument and 

 there is a series of vascular bundles in the nucellus. The testa 

 consists of an outer flesh, the sarcotesta, which may reach a 

 considerable thickness, a shell or sclerotesta, and in some genera 

 an endotesta. In seeds preserved as impressions the sarcotesta 

 often gives them a winged appearance (Samaropsis). The pollen- 

 chamber is relatively small, resembling in this respect the chamber 

 in recent Cycads. A central prolongation of the prothallus- 

 tissue in the form of a blunt column or ' tent-pole ' is a character- 

 istic feature; the same feature occurs in seeds of the Lageno- 

 stomales, but in the Cordaitales it resembles more nearly the 

 'tent-pole/ as it was called by Hirase, in recent Cycadean seeds 

 and in Ginkgo. The presence of two vascular strands in the 

 sarcotesta in the principal plane of the seeds is a character shared 

 with the seeds of Cycas : the position and course of these bundles 

 are useful characters for distinguishing different types within 

 the group. The microspores are multicellular. 



Genera. Cardiocarpus ; Cydospermum ; Cycadinocarpus ; 

 Rhabdospermum ; Mitrospermum ; Diplotesta ; Leptocaryon ; 

 Taxospermum ; Compsotesta. These generic names are all used 

 in the following pages for seeds known to possess certain ana- 

 tomical features; there are also included in the Cardiocarpales 

 the genera Samaropsis, Cordaicarpus, and Rhabdocarpus, but 

 it is proposed to limit their use to specimens which furnish no 

 anatomical data and cannot therefore be assigned with equal 

 confidence to a section of seeds based on definite morphological 

 characters. It is certain that some at least of the seeds described 

 under these names would, if preserved as petrified specimens, 

 be included in one or other of the genera named above. 



There is ample proof that some of these seeds were borne on 

 Cordaitean plants and that the group as a whole represents the 

 seeds of the Cordaitales 1 . It is, however, certain that some 

 Platyspermic seeds were produced by Pt endosperms. No little 

 confusion has been caused by the employment of the same generic 

 names for petrified seeds and for casts and impressions affording 

 no evidence as to similarity in anatomical characters. With 



1 See page 264. 



