XII 



LEPTOSPORANGIA T.E HETEROSPORE^ 



421 



much like them. The curious Ceratopteris suggests a possible 

 connecting form. This strictly aquatic P'crn has the large 

 sporangia with the annulus sometimes incomplete, and the 

 sporophylls modified into pod-like structures which suggest a 

 possible homology with the " fruit " of the Marsiliaceae. The 

 form of the early leaves, too, suggests those of Marsilia. The 

 two genera of the Marsiliaceae are evidently very closely 

 related, and of these Pilularia approaches nearer the homo- 

 sporous Ferns. The accompanying diagram shows the 

 relationship assumed here. 



-izolla 



Eusporangiata 



