92 A TEXT-BOOK OF BOTANY 
plumule that is especially significant, for it develops the 
shoot (Fig. 85). 
Fic. 85.—A series in the germination of the garden bean, showing the hypocotyl 
arch, the pulling out of the cotyledons and the plumule, and the straightening 
of the hypocotyl. 
With the establishment of roots in the soil and the 
exposure of green leaves to the light and air, germination 
is over; for the plant is able to make its own food. 
55. Phototropism.—The stem is sensitive to the direc- 
tion of rays of light, a condition that is called phototrop- 
Fic. 86.—A bean seedling that was placed in a horizontal position and after two 
hours photographed. 
ism, the stem being said to be phototropic. The word 
means ‘directed by the influence of light,’’ the same stem 
