FOLIAGE LEAVES: THE LIGHT-RELATION 13 



Fig. 6. These plants are growing near a windoiv. It will tje noticed tliat the stems 

 bend strongly towards the light, and that the leaves face the liL'ht. 



of tlie most obvious relations of foliage leaves to light, and 

 that the important part Ti'hieh heliotru^iism plavs. not only 

 in connection with foliage leaves, bnt tilso in connection 

 with other plant organs, is one of the most important and 

 extensive sxibjects of plant pliysiologv. 



RELATION- OF LEAVES TO OXE AXOTHEI: 



A. On erect stems 



In view of what has been said, it would seem that the 

 position of foliage leaves on the stem, and their rehition to 

 one another, must be determined to some extent by the 

 necessity of a favoralde light-relation. It is apparent that 

 the conditions of the jOToblem are not the same for tin erect 

 as for a horizontal stem. 



17. Relation of breadth to number of vertical rows. — 

 Uf)on an erect stem it is observed that tlie leaves are usu- 



