78 fl> o s t e i s f a 



root and is essentially different from 

 either, as has been amply demonstrated 

 by several investigators. That many 

 epigean cotyledons should acquire the 

 form of true foliage-leaves is not alto- 

 gether remarkable, for they are func- 

 tionally similar structures in the same 

 environment. 



With our present meager knowledge 

 of the embryology of Gymnosperms, it 

 is a difficult matter to explain the varied 

 unique developments of their embryos. 

 With the exception of Gnetum and 

 Welwitschia, the embryogeny begins by 

 repeated free nuclear divisions within 

 the oosperm. In the conifers the num- 

 ber of nuclei resulting is limited to a 

 few which pass to the base of the 

 oosperm and by free-cell formation 

 organize the proembryo. In the cycads 

 and Ginkgo a large number of free 

 nuclei are produced which in Cycas 



