1NTR0D UCTJON. 287 



Studies in the Relation of Plants to Light. 



Direction of shoots with reference to the source of light; 



compare shoots which have illumination equally on all 



sides with those which are lighted on one side only. 



Direction of branches with reference to the source of light ; 



compare the branching of a tree which has grown in an 



open field with one of the same species which has grown 



in. the forest (in the forest the lower limbs die away when 



they are quite small because the overgrowth of foliage at 



the top of the trees shuts out the light) ; compare also the 



branching of trees at the edge of a forest, or at the edge of 



a clump of trees where one side is strongly lighted and the 



other side is shaded by the adjacent trees. 



Leaf position with reference to access of light can be studied 



during the season when the shoots are clothed with foliage. 



Compare positions of leaves on trees when the foliage is 



dense; the leaves are nearly on the periphery of the tree, 



or at the ends of the branches. Sometimes even in the 



same species, when the foliage is thin at the ends of the 



branches, a great development of leaves and young 



shoots through the centre of the tree takes place. 



Compare position of leaves with reference to position of 



sun at different times of day. On some species the 



leaves are strongly turned, to face the sun, while on 



others the upper leaf surface faces the field of diffused 



light. Compare the compass plant (Lactuca scariola). 



Compare positions of leaves on prostrate stems, and on the 



upright branches of the same. 

 Compare the lengths of petioles when leaves are clustered 



at the base of the shoot, or on a short shoot. 

 Compare the positions of the flowers on trees and other 

 plants with varying density of foliage. 

 Studies in the Relation of Plants to Water. (Water is 

 one of the most important factors in influencing plant life. ) 

 During the growing season observe the effect on different 



