i8o MORPHOLOGY OF GYMNOSPERMS 



Perhaps the most important testimony furnished by such sections 

 as the one just described is as to the condition of detached paleozoic 

 seeds. It is evident that when these seeds had formed a heavy testa 

 and had dropped from the parent plant, there had been no such 

 embryo-formation as takes place in modern gymnosperm seeds before 

 shedding. It may be that fertilization had occurred, and that the 

 proembryo had formed within the archegonium; but it is certain that 

 there had been no further development of the embryo. The absence of 

 embryos from paleozoic seeds, therefore, might be due to the fact that 

 they had not formed when the seed was shed; and therefore the change 

 in later times was a longer retention of the seed before shedding, 

 accompanied by a later maturing of the testa; but more probably 

 the seeds sectioned had dropped prematurely (see p. 47 for a fuller 

 discussion). 



4. History and distribution 



The Cordaitales were contemporaneous with the Cycadofilicales, 

 disappearing from the records in the Devonian, along with the Cycado- 

 filicales, occurring in great profusion during the Carboniferous, and 

 not recognizable beyond the Paleozoic. So far as the historical 

 records go, therefore, the Cordaitales are just as ancient seed plants 

 as are the Cycadofilicales. It is only upon inference from compara- 

 tive resemblance to ferns that a greater age is assumed for the Cyca- 

 dofilicales. 



The geographical distribution of Cordaitales, also, must have been 

 as extensive as that of Cycadofilicales; and they probably formed 

 extensive forests in connection with the arboreous pteridophytes. 

 Their known distribution during the Carboniferous is only limited 

 by our knowledge of the deposits of that period. They must have 

 displayed a profusion of forms and structures that is meagerly shown 

 by their known remains. It is not unreasonable to suppose that a 

 fuller knowledge of their structure and variations will go far toward 

 settling the problems connected with the origin of the later conif- 

 erophytes. 



5. Relationship to other gymnosperms 



The question of the origin of Cordaitales is a choice between two 

 alternatives. They were either derived from the Cycadofilicales, 



