124 ^PHYSIOLOGY. 



traveling around the stem does so in a spiral manner. In the same way, 

 while the end of the stem is moving upward by the elongation of the cells, 

 and at the same time is slowly moved around, the line which the end of the 

 stem describes must be a spiral one. This movement of the stem, which is 

 common to all stems, leaves, and roots, is nutation. 



258- The importance oi nutation to twining stems in their search for a 

 place of support, as well as for the tendrils on leaves or stems, will be seen. 

 In the case of the root it is of the utmost importance, as the root makes its 

 way through the soil, since the particles of soil are more easily thrust aside. 

 The same is also true in the case of many stems before they emerge from the 

 soil. 



