66 posteisia 



In the embryogeny of certain Pterido- 

 phytes there occurs a simple protrud- 

 ing mass of tissue between the root 

 and shoot fundaments the sole function 

 of which is that of a nursing organ, 

 a genuine haustorium, which absorbs 

 nourishment from the gametophytic 

 thallus for the sustenance of the young 

 embryo. It is to the pteridophyte em- 

 bryo in a simple way what the coty- 

 ledon is to the embryo of a Monocot, 

 and is in fact to be considered as a 

 more primitive type of cotyledon. This 

 in brief is an outline of an hypothesis 

 which seems tenable. 



In its ontogeny a seed-plant ex- 

 periences two distinct environments, 

 the one characteristic of its intrasemi- 

 nal life, the other of its extraseminal. 

 The intraseminal life, which begins 

 immediately upon the formation of the 

 oosperm, is passed within a definite 



