THE LIGHT REACTION 



45 



marked when the struggle is severe. If the outside of a 

 plant is densely thatched with leaves, the inside will be 

 found to be comparatively bare. Contrast Figs. 79 and 80, 

 both being views of one tree. We know the tree as seen 

 in Fig. 79: the squirrel knows it as seen in Fig. 80. 



106. On any branch in a very thick-topped tree or bush, 

 leaves of equal age usually tend to be largest where the 

 light is best. Leaves that grow in full sunlight tend to per- 

 sist later in the fall than those that grow in poor light. 

 This fact is sometimes obscured because the outermost 

 leaves are most ex- 

 posed to autumn 



winds. 



107. Plants that 

 start in cellars, from 

 seeds, bulbs, or tubers, 

 grow until the stored 

 food is exhausted and 

 then die: the leaves 

 do not develop to full 

 size in darkness. Figs. 

 81 and 82 show this. 

 Fig. 81 is rhubarb 

 forced in a cellar for 

 the winter market; 

 Fig. 82 is a plant 

 grown out-of-doors. 

 Compare Fig. 45. 



108. The position 

 or direction of leaves 

 is determined largely 

 by exposure to sun- 

 light. In temperate climates, they usually hang in such a 

 way that they receive the greatest amount of light. Observe 

 the arrangement of leaves in Fig. 83. One leaf shades the 



78. A climbing fig choking a palm. 



