GROWTH. 55 



Darwin has shown that the joints of grass stems continue 

 to exhibit movements on a small scale for a long period. 

 Supposing the stem to be "laid," such movements would 

 clearly aid the upward tendency above described, and 

 facilitate the uprising of the stem. (Darwin, Power of 

 Movement, p. 503). 



MoTements of Leaves, The leaves of plants exhibit 

 several kinds of motion ; some periodic, as in the case of 

 the so-called sleep of leaves, some due to the stimulus of 

 light or its removal, some the consequence of contact, as 

 in the case of the sensitive plant; but those to which 

 mention is here made are the result of the same causes as 

 those before alluded to in the case of stems and roots. 

 The growth movements of leaves are observable in the 

 stalk, or in the blade, or in both, and are chiefly exerted 

 in a vertical direction, so that the leaf rises or falls ; but 

 as the ascent is never quite in fche same line as the de- 

 scent, some side to side motion must also take place. It 

 is noticed that the rise occurs generally in the evening, 

 the fall on the following morning. These movements 

 are probably due to the intensity of growth being greater 

 first on one side, then on the other. 



Growth-movements of the kind indicated have now 

 been shown to exist in the roots, in the stems, and in the 

 leaves. The probability is that they occur more or less 

 wherever growth is going on actively. In accordance 

 with this, it maybe mentioned that seedling plants mani- 

 fest these movements to a remarkable degree. Thus- all 

 the parts of seedling cabbages, the radicle, the caulicle 

 above the radicle supporting the seed leaves or cotyle- 

 dons, as well as these latter organs, were observed by 

 Darwin to exhibit growth movements facilitating the 

 downward passage of the root and the upward progress 

 of the caulicles f 



