104 PLANT LIFE 



what a thin, cord-like organ the ordinary 

 young root is. 



Farther back from the growing point the 

 mechanical function of the root, as already 

 stated, is that of holding the plant in the soil. 

 The most effective position for the mechanical 

 tissue to occupy to withstand pulls from 

 various directions is along the centre or axis 

 of the organ. For in this position the stress 

 is most evenly distributed. Indeed, the me- 

 chanical strands may be regarded as cables 

 in this form of construction. 



Sometimes it happens that a root has to 

 discharge still more complex mechanical 

 functions, and its structure in this respect 

 may then vary accordingly. The Indian corn 

 plant, for example, has a thick stem, large 

 leaves, and heavy fruit (Fig. 14). The rooting 

 end where it penetrates the ground is quite 

 thin, and the plant is obviously top-heavy, 

 but a circle of roots springs from each of 

 the nodes of the stem, that succeed each other 

 at very short intervals just above the level 

 of the ground, and each root grows towards 

 the soil in a more or less arched manner; 

 in this way the plant as a whole is well 

 supported by means of a series of arched 

 struts which admirably enable it to over- 

 come the mechanical disadvantages of its 

 original conformation. Now it is clear that 

 when the plant is exposed to a force tending to 

 bend it, the roots on the side towards which 

 it inclines to fall over are exposed to crushing 



