70 posteista 



dinae is developed entirely from tissues 

 of epibasal origin. In the Filicinse and 

 Equisetinse the foot is developed from 

 a part or the whole of the hypobasal 

 cell, without additions of epibasal 

 tissue. 



An explanation of this displacement 

 of the foot primordium in these cryp- 

 togamic embryos is to be sought in the 

 changing inter- relationship of the sporo- 

 phyte and gametophyte, and the grow- 

 ing importance of the free life of the 

 sporophyte. The ultimate independence 

 of the latter was realized through the 

 evolution of a new structure, the root. 

 Whether the root primarily arose as a 

 terminal or lateral structure, from tissue 

 of epibasal or hypobasal origin, is a 

 matter of speculation and of little im- 

 portance to our present discussion. In 

 either case as the sporophyte came to 

 pass the greater part of its life as an 



