68 



PLANT RELATIONS. 



48. Relation to light. As stems bearing foliage leaves 

 hold a special rela'ion to light, it is necessary to speak of 

 the influence of light upon the direction of growth, an 



FIG. 59. 



An elm in foliage, showing the breaking up of the trunk into branches and 

 the spreading top. 



influence 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). 



