THE GYMNOSPERMAE : CYCADALES, ETC. 



767 



contains nutritive endosperm and there is a lateral outgrowth of the hypocotyl, 

 the foot, which remains inside the seed coat and acts as an absorber of 

 nutriment from the endosperm. This recalls the similar embryonic structure 



OOSPHERE 



POLLEN TUBE 



MALE NUCLEI 



SUSPENSOR 



EMBRYONAL 

 NUCLEI 



OOSPHERE 



1^ 





OOSPORE 



SUSPENSOR 



EMBRYO 



CELLULAR PART 



OF GAMETOPHYTE 



Fig. 767. — Gnetum gnemon. Fertilization and development of the embn-o. A, Differ- 

 entiation of the oosphere nuclei in the embryo sac. B, Embryo sac after fertiliza- 

 tion. C, First division of the oospore to form the suspensor. D, Lower end of 

 elongated suspensor showing primary embryonal nuclei. E, Early embryo 

 development. (After Thompson.) 



in many Pteridophyta, though there is probably no direct relationship 

 involved. The hypocotyl soon thickens into a small tuber and the stem apex 

 produces two leaves, at right angles to the cotyledons, which, like the 

 cotyledons, are at first erect. By the end of the first year all four have become 

 horizontal. After two or three years the cotyledons drop off, but the two 

 leaves remain permanently (Fig. 769). The growing point of the stem aborts 

 and no further growth in length takes place. At a ver)' early stage two little 



