LEAVES 



9 



cannot be covered by a general rule, except that it seeks 

 to get all the light it can without danger. How leaves seek 

 the light will be first considered, and later how they protect 

 themselves against it. 



(1) Horizontal position. The ordinary position of the 

 leaf is more or less horizontal. This enables it to receive 

 the direct rays of light upon its upper surface, and more 

 rays strike it than if it stood obliquely or on edge. Most 

 leaves when fully grown are in a fixed position and cannot 

 change it, however unfavorable it may become; but there 



PIG. 4. Geranium leaves exposed first to vertical (A) and then to oblique (B) 



*rays of light. 



are leaves so constructed that they can shift their position 

 as the direction of the light changes, or the stem bearing 

 the leaves may shift its position so that a better relation to 

 light is secured (Fig. 4). If a garden nasturtium growing in 

 a window be observed, its leaves will be seen facing the 



