382 



EMBRYO OF ANGIOSPERMS 



varying amount of endosperm, which in turn is surrounded with 

 sporangial cells or perisperm, as in the water lily (Fig. 276, B). 

 The integument usually undergoes pronounced changes during 

 this growth, becoming hard and tough to protect the parts within, 

 and often developing appendages of various kinds, as hairs and 

 wings, to promote the distribution of the seed (see gymnosperms, 

 page 358). 



B 



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

 ium. 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 plum.ule. 

 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 endosperm. 

 B, section of seed of water lily (after Conard) — e, embryo, surrounded by a 

 layer of endosperm cells; mg, cells of the megasporangium; i, integument. 



The stimulus of fertilization extends beyond the changes 

 wrought in the sporangium. This is particularly noticeable in 

 the megasporophyll and often in adjacent parts which keep pace 

 with the growth of the sporangium and often undergo remarkable 

 transformations. The result of this total growth is called the 

 fruit, while the term seed is restricted to the modified sporangium 

 with its integument and embryo. The megasporophyll may form 



