126 
THE VEGETATIVE FUNCTIONS OF PLANTS 
responds by growing either more or less rapidly, as the 
case may be. 
127. Relation of Roots and 
Stems to Gravity. It is common 
knowledge that, in general, roots 
grow downward, while stems 
grow upward. If a germinating 
seed of lupine is so placed that 
the axis of the emerging embryo- 
plant is horizontal, the position 
of the elongating root and shoot 
after a given interval of time 
(e.g. 48 hours) will be as shown 
in Fig. 84. The result is the 
same whether the plant is placed 
in diffused light or in the dark. 
The difference in the direction of 
growth may not, therefore, be 
attributed to the action of light. 
If the seedling is so placed that 
the only external influence is 
gravity the attraction of the 
earth the result is as shown in 
the figure. We must, therefore, 
conclude that the result is due 
to the earth's gravitational at- 
Fig. 84. Seedling of white 
lupine (Lupinus albus), after traction, 
having been placed horizon- 
tally in the dark for 48 hours. 
The hypocotyl (h) has re- sion may be assured by subject- 
to 
The correctness of this conclu- 
ulus of gravity. The portion ence than gravity, but, like it, 
(o) remains in the original . , , , , 
horizontal position. acting on both root and snoot, at 
