DEVELOPMENT OF PLANTS 



395 



nosperm, and it serves the same purpose, namely, to nourish the 

 young sporophyte or embryo. Recall, however, that it originates 

 in a different manner and at a different time in the life cycle. 

 The germination of the gametospore and the formation of the 

 embryo vary so greatly that only a very general statement can 

 be made. Following fertilization, the gametospore becomes sur- 

 rounded by a cell wall and attached to the wall of the embryo 

 sac (Fig. 275, A). It now begins to elongate and its nucleus 

 divides several times, forming a row of cells (Fig. 275, A, B}. 

 This is the proembryo, the terminal cell being known as the 

 embryo cell and the remaining cells as the suspensor. Less 



FIG. 274. Sectional view of megasporophylls of Lepidium shortly after 

 fertilization (see Fig. 269); en, early development of endosperm cells about 

 wall of embryo sac; p, young sporophyte developing from gametospore; 

 mi, micropyle; s, stigma;/, funiculus. 



commonly the proembryo is a mass of cells without any differ- 

 entiation. This appears as a radical departure from the gymno- 

 sperms where the formation of free nuclei characterized the 

 germination of the gametospore. But in passing from the cycads 

 to the pines there is a steady decline in the number of free cells 

 formed and indeed in our case in the latter group the proembryo 



