CYCADOFILICALES 5^ 



not exist even as haustoria is evidenced by the fact that pollen grains 

 with no tubes are found in contact with the megaspore membrane. 

 Scott (87) has called attention to the very interesting fact that in 

 1887 Renault (12), in describing the structure of Aetheotesta, a 

 seed allied to Stephanospermum, anticipated through inference the dis- 

 covery of swimming sperms among gymnosperms. In both of these 

 genera the walls of the pollen grains are perforated, and Renault 

 suggested "that these perforations served for the passage of motile 

 bodies analogous to antherozoids." He adds, "we do not regard as 

 impossible the existence in the past of pollen grains which, instead of 

 effecting fertilization by means of a tube, discharged into the pollen 

 chamber of the appropriate seeds antherozoids capable of performing 

 this function." 



4. History and distribution 



That Cycadofilicales were a dominant group during the Carbon- 

 iferous, and that they were to be found in abundance wherever the 

 vegetation of the Coal-measures occurred, are facts that seem to be 

 clearly established. It is scarcely less clear that they existed during 

 the Devonian. Kidston (64) thinks that they are plainly repre- 

 sented in remains of the Upper Devonian; and there are suggestions 

 of still greater age. This means that they can be traced to a time so 

 remote that no other group of vascular plants, or at least fernlike 

 plants, is known to antedate them. The type is distinctly paleozoic, 

 for, although it culminates during the Coal-measures, no trace of it 

 has been discovered in the Mesozoic. From their history, their 

 structure, and their resemblance to ferns, therefore, the Cycadofili- 

 cales may be regarded as the most archaic group of spermatophytes 

 known. 



5. Relationship to ferns 



At the first discovery of fernlike seed plants, it was natural to infer 

 that this group must have arisen from the so-called Marattia plexus 

 which was thought to be dominant in the Carboniferous. Subsequent 

 discoveries of seed-bearing plants made serious inroads upon this 

 "plexus," and finally the discovery of the fernlike microsporangiate 

 structures of the Cycadofilicales left the whole question of paleozoic 



