postelsia 77 



ous cotyledons which result through 

 a greater or less degree of response 

 to the divers influences surrounding the 

 intraseminal life need not be enumer- 

 ated here. 



The assumption of the vegetative 

 habit by some cotyledons is a natural 

 outcome of their becoming epigean upon 

 the germination of the seed. For all 

 portions of the seedling exposed to the 

 light produce chlorophyll to provide 

 for the immediate needs of the young 

 plant. The cotyledons usually become 

 epigean through the elongation of the 

 hypocotyl, a structure appearing for the 

 first time among the Angiosperms. Its 

 development was made possible by the 

 fact that the cotyledons need not remain 

 in or at the surface of the soil during 

 germination — a condition arising with 

 the seed-habit. The hypocotyl is differ- 

 entiated between the primary stem and 



