EACH LEAF LOOKS FOE LIGHT 



45 





the light is best. 

 Leaves which grow 

 in full sunlight 

 tend to persist later 

 in the fall than 

 those which grow 

 in poor light (Fig. 

 77). This fact is 

 sometimes ob- 

 scured because the ''''^' '^^^ branches have grown towards the light. 



outermost leaves are most exposed to autumn winds. 



106. Plants which 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. 78 and 79 show this. Fig. 78 is rhu- 

 barb forced in a cellar for the winter market; Fig. 79 

 is a plant grown out-of-doors. Compare Fig. 42. 



107. The position or direction of leaves is determined 



largely by exposure to sun- 

 light. In temperate cli- 

 mates, they usually hang 

 in such a way that they 

 receive the greatest 

 amount of light. Ob- 

 serve the arrangement 

 of leaves in Fig. 80. 

 One leaf shades the other 

 to the least possible de- 

 gree. If the plant were 

 placed in a new position 

 with reference to light, 

 the leaves would make 

 an effort to turn their 

 ,., „ ., , , . ^, , , blades. Observe the 



VJ. Mantle of clematis. The leaves, and later 



the flowers, spread themselves to the light. shiugle -like arrangement 



