GERMINATION OF SEEDS 95 
versely phototropic. The adjust- 
ment of the leaf-blades to the 
new direction of the light may 
be seen in Fig. 87. 
The root also is phototropic, 
turning directly away from the 
source of light; that is, it is 
negatively phototropic. Fig. 88 
shows a seedling of white mus- 
tard so arranged that both stem 
and root are exposed only to 
weak light, the former showing 
positive, the latter negative 
Li 
Fic. 89a.—First stage of the 
series shown in Tig. 89; one 
cotyledon removed to show 
the relation of parts, and the 
arch developed by the first 
internode. 
phototropism. It is 
interesting to note 
that a tap-root be- 
ing positively geo- 
tropic, positively hy- 
drotropic, and nega- 
tively phototropic, all 
of its responses under 
ordinary conditions 
combine to direct it 
into the soil. 
56. Other seeds.— 
Tic, 90.—Seedling of castor-bean, showing large 
It must not be sup- and green cotyledons. 
