CHARACTERISTICS OF LEAVES 



101 



Submerged leaves are usually linear or thread-like, or are 

 cut into very narrow divisions.- Thereby is more surface ex- 

 posed, and possibly the leaves are less injured by moving 

 water. 



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151. Elliptic leaf 

 of purple beech. 



—J 



152. Ovate serrate leaf 

 of hibiscus. 



215. The largest leaves on a sun-loving plant are usually 

 those that are fully exposed to light. Compare the sizes of 

 the leaves on the ends of branches with those at the base of 

 the branches or in the interior of the tree-top (106). In 

 dense foliage masses, the petioles of the lowermost or under- 

 most leaves tend to elongate — to push 

 the leaf to the light. (Fig. 157.) 



216. On the approach of winter the 

 leaf ceases to work, and often dies. 

 It may drop, when it is said to be de- 

 ciduous; or it may remain on the plant, 

 when it is said to be persistent. If 

 persistent leaves remain green during 

 the winter, the plant is said to be 

 evergreen. Most leaves fall by break- 

 ing off at the lower end of the petiole 

 with a distinct joint or articulation. 

 There are many leaves, however, that wither and hang 

 on the plant until torn off by the wind: of such are the 



154. Truncate leaf of 

 tulip-tree. 



