380 ANGIOSPERMS 



cellular embryo. This divides into two cells of which that 

 nearest the micropyle becomes the suspensor (E, spsr\ the 

 other or embryo proper (emb) forming a solid aggregate of 

 cells, the polyplast. By further differentiation rudiments of 

 a stem (F, si), a root (r) and either one or two cotyledons 

 (ct) are formed, and the embryo passes into the phyllula 

 stage. 



While the early development of the embryo is going on 

 the secondary nucleus of the megaspore divides repeatedly 

 and, the products of division (E, nu) becoming surrounded 

 by protoplasm, a number of cells are produced, which, by 

 further multiplication fill up all that part of the megaspore 

 which is not occupied by the embryo. The tissue thus 

 formed is called the endosperm (F, end\ and occupies pre- 

 cisely the position of the vestigial prothallus of Gymnosperms 

 (Fig 88, p. 370, D, prth) and E, end : and p. 372), differing 

 from it in the fact that it is only formed after fertilization. 

 We have here a case of retarded development : the degenera- 

 tion of the prothallus has gone so far that it arises, by free 

 cell-formation, long after the formation of the ovum which? 

 in both Gymnosperms and vascular Cryptogams, is a 

 specially modified prothallial cell. 



The phyllula continues to grow and remains inclosed in 

 the megasporangium which undergoes a corresponding in- 

 crease in size and becomes the seed. One or more seeds 

 also remain inclosed in the venter of the pistil which grows 

 considerably and constitutes the/ra/V. Finally the seeds are 

 liberated, the phyllula protrudes first its root, and then its 

 stem and cotyledons through the ruptured seed-coat, and 

 becomes the seedling plant. 



We learn from the present lesson that there is a far greater 

 uniformity of organization among the higher plants than 



