68 



PLANT STUDIES 



48. Relation to light. — As stems bearing foliage leaves 

 hold a special relation to light, it is necessary to speak of 

 the influence of light upon their direction, the response to 



Fig. 5'J. Al. ciLu u. loliage, ahuwun^ die breaking up of the truiik into uiaucucy ana 

 the spreading top. 



which is known as heliotropism, already referred to under 

 foliage leaves. In the case of an erect stem the tendency 

 is to grow towards the source of light (see Figs. 1, 64). 



