DEVELOPMENT OF PLANTS 391 



the power to grow and form a tissue that supplements the anti- 

 podal cells and so takes the place of the nourishing gametophyte 

 of the gymnosperms. According to this view, the endosperm is 

 a delayed prothallial growth which does not take place until 

 fertilization is effected. There is considerable evidence to justify 



Fig. 271. Section of a megasporangium of lily, showing the mature female 

 gametophyte: 9, female gamete, below which are two synergids; p, the 

 two polar nuclei uniting to form the endosperm nucleus; a, antipodal cells; 

 mi, micropyle; i, integuments; /, funiculus in which a vascular bundle, i), 

 has been formed to transport foods to the sporangium. 



this conclusion. In the Pteridophyta the archegonia are formed 

 at the close of the prothallial development. Among the species 

 of the Gymnospermae there are several examples indicating that 

 the archegonia are formed at earlier and earlier stages in the 

 development of the gametophyte (p. 367). Possibly we have in 

 the Angiospermae a final condition where the homologues of the 



