AGRICULTURAL BOTANY 



129 



Darwin discovered that the root tip in its search 

 for plant food and moisture does not move straight 

 forward, but seeks for the line 

 of least resistance. As it thus 

 takes advantage of openings 

 in the soil, an oscillating, or 

 pendulum-like, movement re- 

 sults. 



Branching of Roots. The 

 roots of the annual crops 

 grown on the farm branch 

 very freely. This is equiv- 

 alent to saying that they can 

 take up a large amount of 

 moisture and food from the 

 soil, because the greater the 

 number of root branches, the 

 greater the number of root +/ 

 hairs, or absorbing surface of 

 the root. The root branches 

 usually spread out over the 

 part of the soil pulverized by 

 the plow, for here the plants 

 seem to find the greatest 

 amount of nourishment. 



The rapid way in which 

 roots will branch under favor- 

 able conditions may be shown by burying a piece 

 of manure in the soil near a plant. In a short time the 

 plant will send its rootlets in all directions through it. 

 An old bone, which contains an abundance of plant 

 food, when buried under the surface of the ground is 

 often found covered with a thick net of fibrous roots. 

 M. & H. AG. 9 



-rt 



FIG. 54. Roots of Young Wheat 

 Plant. 



rh, root hairs, surrounded by grains of 

 soil; rt, root tips. 



