SHOOTS 69 



This has the general result of placing the leaf hlades at 

 right angles to the rays of liglit, and in tliis respect the 

 heliotropism of tlie stem aids in securing a favorahle leaf 

 l")osition (see Figs. iV.], G:]«). Prostrate stems are dilTerently 

 affected by the light, however, heing directed transversely 

 to the rays of light. The same is true of many foliage 



Fui. 00. An u;ik in ils wiiilcr eonditinn. t^linwiiig tllc wIiIl' l)ra-irhini:. Tl;t^ \;iriiiup 

 dirtclions vf tliu branches liavc been determined bv the liglit-relationy. 



branches, as may 1)e seen by observing almost any tree in 

 wliich tlie lower branches are in the general transverse posi- 

 tion. Tliese liranches generally tend to turn upwards when 

 the]' are Ijeyond the region of shading. Subterranean 

 stems are also inostlj' horizontal, but they are out of tlie 

 influence of light, and under tlie influence of gravity, 

 known as geotropism, which guides them into the trans- 

 verse position. The climbing stem, like the erect one. 



