CHAPTER FOUR 



Note the alternate 



arrangement of the leaves. 



LEAVES IN RELATION TO LIGHT 



THE leaf, as we have seen, must receive light in order to 



produce food. Leaves are variously arranged on stems, and 



stems have all sorts of positions. 



Many of these leaf arrangements and 



stem positions are not advantageous 



for the display of leaves to the light. 



The leaf, however, and especially the 



petiole, is so influenced by light dur- 

 ing its development, that the leaf 



when mature has the best possible 



position with respect to light. The 



raised leaves of the pumpkin, the FIG. 21. Vertical branch of 



mosaics of leaves formed on the sides 



of buildings by the* Boston ivy, and 



the successive tiers of leaves on a beech tree illustrate 



different arrangements by which large numbers of leaves 



are efficiently displayed to the light. 

 The arrangement of leaves on stems. Leaves develop 



from somewhat thickened places on the stems, called the 



nodes. Each node 

 may bear one, two, 

 or several leaves. 

 According to the 

 number of leaves 

 that the node 

 bears, the leaf ar- 

 rangement is desig- 



FIG. 22. Horizontal branch of magnolia. Compare leaf 



positions with those of Figure 21. Opposite, 



37 



