39 THE GROWTH AND PARTS OF PLANTS 
from the end than in the root. This 1s because the 
region of elongation or motor zone im the stem is farther 
from the tip than in the root. 
How gravity influences the stem. It may seem re- 
markable that gravity, which influences the root to 
STOW downward, also influences the stem to grow 
upward. It is nevertheless true. The lateral roots 
and lateral stems are influenced difter-— 
ently. What are the advantages to ger- 
minating seeds from this fluence of 
gravity on root and stem? 
Behaviour of the roots toward moisture. 
Test this by planting seeds in a long box, 
keeping the soil in one end dry and inv 
= the other end moist. The root grows 
aes ake toward moist places in the soil. If the 
upward. soil is too wet, the roots of many plants 
grow away from it. Sometimes they grow out on the 
surface of the soil where they can get air, which they 
cannot get if the soil is too wet. 


