XIV ISOETACE^ 561 



The development of the spores and tlie early stages of the 

 female g'ametoph}te certainly resemble those of Sclagiiiclla, 

 and form the strongest argument for assuming a relationship 

 between the two genera. The embr}'o, h(j\ve\er, is very much 

 more like that oi the eusporangiate Ferns, resembling, ])erhaps, 

 most nearly that of Bofrycln'mn, and in connectirm with the 

 structure of the mature gametophyte and sexual organs, makes 

 it not improbable that there is a real, but extremely remote rela- 

 tionship Ijetween Isoctcs and the Eusporangiatic. 



As to the affinities of Isoefcs with the Spermatophytes, it 

 more nearlv resembles them in the formation of the female 

 prothallium than any other Pteridophyte except Selaginclla, and 

 the reduction of tlie antheridium is even greater than there. 

 The embryo resembles very much tliat of a ty])ical Monocotyle- 

 don, and the histology of the fully-developed sporophyte, the 

 leaves with their sheathing bases surrounding the short bulb- 

 like stem, and the structure of the roots, all suggest a possible 

 relation to the Alonocotyledons directly rather than through the 

 Gymnosperms. 



There is, however, a great interval between the flower of 

 the simplest Angiosperm and the sporophylls of Isoetcs, and 

 more evidence must be produced on the side of the former 

 before it can l)e asserted that this relationship is anything more 

 than apparent. 



36 



