364 



EMBRYO OF ANGIOSPERMS 



Among the monocotyledons, the embryo cell frequently produces 

 the single cotyledon, while the next underlying cell of the sus- 

 penses forms the root and the laterally-placed growing point of 

 the stem (Fig. 279). The pro-embryo of dicotyledons is fre- 

 quently a filament of cells of varying length and the embryo 

 cell, by a regular service of divisions, gives rise to the stem, two 

 laterally-placed cotyledons and all of the root, save the tip, which 

 is formed from the cells adjoining the embryo cell (Fig. 276, A). 



B 



Fig. 276. Seed structure : A, section of a nearly mature seed of Lepid- 

 iiim. The stem of the embryo is differentiated below into a hypocotyl, hy, 

 and above into an epicotyl, pi, commonly known in the seed as the plumule. 

 r, root with root cap ; c, the two cotyledons, which are bent over, lying 

 one upon the other; v, vascular bundles extending through the stem into 

 the cotyledons, where they form a network of veins; en, remains of endo- 

 sperm. B, section of seed of water lily (after Conard) — e, embryo, sur- 

 rounded by a layer of endosperm cells ; mg, cells of the megasporangium ; 

 i, integument. 



128. The Fruit and Seed. — -Various changes occur in the 

 sporangium during the growth of the embryo. More frequently, 

 perhaps, the embryo sac enlarges, absorbing all the cells within 

 the integument, and it becomes filled with endosperm cells. In 

 a case like this, the embryo either remains small and embedded 



