EACH BRANCH LOOKS FOR LIGHT 43 



pot or pan. When the plants are three or four inches 

 high, place the pan in a tight box which has a hole on 

 one side. The next day it will look like those in Fig. 70. 

 This turning towards the light is called heliotropism 



(helios is Greek for "sun.") 



101. Even under natural con- 

 ditions, plants become misshapen 

 or unsymmetrical if the light comes 

 mostly from one direction . On the 

 edge of a forest, the branches 

 reach out for light (Fig. 71) 

 Trees tend to grow a,way from a 

 building. Branches become fixed 

 in their position, so that even 

 in winter they tell of the search 



70. Searching for light. f or light (Fig. 72). 



102. 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 sometimes choke and smother the plant 

 on which they climb. This they may do by throwing 

 their mantle of foliage over it, and smothering it, or by 

 sending their roots into its trunk and robbing it of food. 

 Sometimes they do both, as in Fig. 74. Every plant has 

 a story to tell of the value of sunlight. 



103. EACH BRANCH LOOKS FOR 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. 



104. EACH LEAF LOOKS FOR LIGHT. Leaves are borne 

 towards the ends of the branches. This is particu- 



