MORPHOLOGY 



45 



united as to appear but a single organism ; as, for example, in the 

 Mosses, where the spore-producing generation lives upon the sexual 

 plant, or as in Phanerogams, where, conversely, the sexual generation 

 completes its development within the asexual plant. 



In Phanerogams, owing to the formation of the embryo within 

 seeds, that stage of the development of a plant which is termed 

 germination is clearly defined ; for not until the seed is completely 



Fig. 4(i.— Thvjaocciclentalis. .4, Median longitudinal 

 section through the ripe seed (x5); B, C(x2); 

 D, E (nat. size), different stages of germina- 

 tion ; hy hypoeotyl ; c, cotyledons ; r, radicle ; 

 t; vegetative cone of stem. 



Fig. 47. — Seedling of Car^inus Betulus. h, 

 Hypoeotyl ; c, cotyledons ; liw, main 

 root ; sw, lateral roots ; r, root-hairs ; e, 

 epicotyl ; I, V, foliage leaves. (Nat. size.) 



formed does the newly-formed plantlet begin its independent exist- 

 ence. The embryo, while still enclosed within the seed, generally 

 exhibits the segmentations characteristic of Cormophytes. Protected 

 by the hard seed-coats, it is enabled to sustain a long period of rest. 

 Abundant deposits of nutritive material in the embryo itself, or 

 surrounding it, are provided for its nourishment during germination. 

 The different segments of a phanerogamic embryo have received 

 distinctive names ; thus, as in the embryo of the American Arbor Vitae 

 (Thuja occidentalis, Fig. 46), the stem portion (h) is termed the HYPO- 



