44 



PLANTS AND SUNLIGHT 



which has a hole on one side. The next day it will look 

 like those in Fig. 75. This turning toward the light is 

 called heliotropism (helios is Greek for "sun"). 



102. Even under natural 

 conditions, plants become 

 misshapen or unsymmetri- 

 cal if the light comes 

 mostly from one direction. 

 On the edge of a forest, 

 the branches grow out 

 toward the light. (Fig. 76.) 

 Trees tend to grow away 

 from a building. Branches 

 become fixed in their 

 position, so that even in 

 winter they show the in- 

 fluence of light. 



103. Some plants climb 

 other plants in order to 

 reach the sunlight; or they 

 climb rocks and buildings. Notice that the vine on the house 

 luxuriates where it is lightest. Climbing plants may injure 

 or even kill the plant on which they climb. This they may 

 do by throwing their mantle of foliage over it, and smother- 

 ing it, or by sending their roots into its trunk and robbing 

 it of food. Sometimes they do both, as in Fig. 78. 



104. Each Branch Grows Toward Light. The plant is 

 made up of branches. There is a struggle amongst the 

 branches for sunlight. We have seen (Fig. 7) that no two 

 branches are alike: we now know one reason why. Notice 

 that the small branches die in the center of the tree. Look 

 on the inside of a pine, spruce or other dense tree. Every 

 branch has a story to tell of the value of sunlight. 



105. Each Leaf Grows Toward Light. Leaves are borne 

 toward the ends of the branches. This is particularly 



77. Mantle of clematis. The leaves, and later 

 the flowers, spread themselves to the light. 



