THE ROOT 
37 
includes the hypocotyl; the two are usually indistinguishable 
except by the internal structure. The primary root is 
strongly geotropic and hydrotropic, and negatively helio- 
Fig. i. Germination of Gourd (Cucurbita, q.v.). 
A , the seed. B , seed laid open, showing one veined cotyledon and 
the hypocotyl-radicle. C , the radicle, by the growth of the hypocotyl, 
has emerged from the seed-coat and is growing down geotropically. 
D , the peg has caught on the seed-coat, while the growth of the arched 
hypocotyl has nearly freed the cotyledons. E , the cotyledons are 
freed and the hypocotyl has become straight. E, the first foliage-leaf 
has developed from the plumule. 
tropic ; it therefore grows on the whole straight downwards, 
but may curve towards moisture. 
The tip of the growing point is covered by the root-cap , 
an organ peculiar to roots, consisting of a sheath of cells 
