4o8 



MOSSES AND FERNS 



CHAP. 



sporophyte breaks away from the spore or carries the latter 

 with it to the surface of the water. As the embryo breaks 

 though the episporic appendages at the top of the spore, these 

 are forced apart and the cap-shaped summit of the indusium is 

 thrown off. The cotyledon is funnel-shaped, with a cleft on 

 one side, and completely surrounds the stem apex. The root 

 is still inconspicuous, and forms only a slight protuberance 

 upon one side of the foot, which looks like a short cylindrical 

 stalk (Fig. 237). 



Fig. 238. — Salvinia natans. A, Horizontal section of the stem apex, X4S0; L, young 

 leaf; B, a young leaf, showing the apical cell (x), X450; C, longitudinal section 

 of a segment of a ventral leaf, X450; D, section of a dorsal leaf; i, lacunae; h, 

 hair, X22S; E, cross-section of the stem, X50; F, the vascular bundle, X225. 



The growth of the first root is limited, and it differs from 

 the later ones by forming peculiar stiff root-hairs. Tlie later 

 roots, except the second, do not seem to bear any definite rela- 

 tion to the succeeding leaves. 



A careful examination of the ripe macrosporangium shows 

 a number of colourless small round bodies occupying the space 



