46 MORPHOLOGY OF GYMNOSPERMS 



beak, which is an extension of the ribbed bony layer often as long 

 as the body of the seed (in some specimens twice as long) and bears 

 two broad wings. 



It is evident that at least two types of structure are known among 

 paleozoic seeds, which may be called the Lagenostoma type and the 

 Stephanospermum type, the former known to belong to the Cycado- 

 filicales, the latter very probably including seeds that must be referred 

 to the same group. There are certain features in common, however, 

 that should be noted. 



A character shared by all paleozoic seeds whose structure is known 

 is the presence of a pollen chamber. Occurring as a circular crevice 

 in Lagenostoma and as a broad chamber in Stephanospermum, it 

 indicates in both the existence of swimming sperms. So far as the 

 evidence goes, therefore, the abandonment of swimming sperms by 

 seed plants did not begin until after the Paleozoic. It is noteworthy 

 that the largest pollen chambers seem to have been attained by the 

 Stephanospermum type as displayed in the Permian, a type which 

 perhaps has no successors. 



Perhaps the most puzzling fact discovered in connection with 

 paleozoic seeds is the entire absence of any indication of an embryo. 

 That embryos are preserved in petrifactions is evidenced by their 

 abundant occurrence in the seeds of the mesozoic Bennetti tales. 

 Oliver (38) has suggested that perhaps the long intraseminal period 

 of the embryo of seed plants had not been developed in the Paleozoic; 

 but the abundant endosperm invested by an efficient testa seems to 

 be against this view. Accepting the absence of embryos from paleo- 

 zoic seeds as a fact, it should be remembered that the proembryo 

 of the more primitive gymnosperms is quite extensive, and that even 

 were it preserved it would hardly be recognized as an embryo. So 

 far as any record to the contrary has shown, all this proembryonic 

 development may have taken place in the preserved paleozoic seeds. 

 It seems possible, therefore, that the paleozoic seeds matured (develop- 

 ing testa) before fertilization, became detached after pollination, and 

 subsequently developed a proembryo which did not invade the endo- 

 sperm before germination, or invaded it in a very feeble way as 

 compared with the extensive invasion in modern gymnosperms. Check- 

 ing the growth of the embryo, if it is related to the organization of a 



