68 PLANT STUDIES 
48. Eelation to light. As stems bearing foliage leaves 
hold a special relation 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, G4). 
