124 ^PHYSIOLOGY. 



traveling around, the stem dues so m a spiral manner. In tlie same way, 

 while the end. of the stt-m is nn.iving upward by the elongation of the cells, 

 and at the same time is slowl}'' muvcd anmnd, the line which the end of the 

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

 conim.on to all stems, leaves, and roots, is nutation. 



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

 place of support, as well as fur 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 ib also true in the case of many stems before they emerge from the 

 soil. 



