DEVELOPMENT OF PLANTS 317 



phyte is quite small. They usually project from the surface of 

 the thallus as spherical bodies covered with a single layer of 

 chlorophyll-bearing cells which inclose usually from thirty-two 

 to sixty-four gamete-bearing cells (Fig. 229, A). The male 

 gametes are discharged as in the Bryophyta — the swelling of the 

 antheridium causes the rupture or throwing off of the apical cell 

 and the extrusion of the inner cells as a mucilaginous mass. The 

 gametes are large spirally-coiled bodies provided with numerous 

 cilia and the larger posterior coils enclose a delicate sac containing 

 the remains of the nourishment stored in the mother cell (Fig. 



229, B). The archegonia are developed on the older prothallia, 

 usually just back of the growing point (Fig. 228, C). The neck 

 of the archegonia, consisting of four rows of cells, projects from 

 the under surface of the prothallium and is usually curved back 

 from the growing point, while the basal portion containing the 

 female gamete remains buried in the tissues of the prothallium 

 (Fig. 229, C). When the female gamete is mature the canal 

 cells become mucilaginous and the lip cells open as in the arche- 

 gonium in the mosses. 



(c) Germination of the Gametospore. — The gametospore ger- 

 minates in a week or more after fertilization, dividing very regu- 

 larly first by a vertical and later by a transverse division into four 

 cells. Each of these cells forms a primary organ of the young 

 sporophyte. Of the two outer cells, the one nearer to the grow- 

 ing point of the prothallium (Fig. 230, A, c) by repeated divi- 

 sions produces the first leaf or cotyledon, while the other one 

 forms the first root (Fig. 230, A, r). Of the two lower cells, 

 the one directly below the leaf cell gives rise to the stem (Fig. 



230, A, s) and the other one to the foot (Fig. 230, A, f). The 

 growth of these four cells results at first in the formation of a 

 rather globular sporophyte, but soon the growing point of the 

 young root grows through the calyptra, turns downward and 

 penetrates the soil (Fig. 230, B). This is followed by emerg- 

 ence of the cotyledon, which, however, curves upward and spreads 

 out its blade to the light (Fig. 231). Note in Fig. 230 that the 

 necessities of the plant have determined the position of these 

 four organs. The foot is formed in contact with the bulk of the 



