CHAPTEE X 



LEAVES 



103. The leaf as a member of the plant body. Among seed 

 plants the plant body consists of root and shoot. The latter 

 is made up of stem and leaves. It is diffi- 

 cult to frame a simple and exact definition 

 for the leaf, but every one is sufficiently 

 familiar with the appearance of the ordi- 

 nary foliage leaves of plants, and there is 

 no difficulty in identifying these. The un- 

 usual scale-like, bristle-shaped, tendril- 

 shaped, or pitcher-form leaves are often 

 hard to recognize as such. 



104. Parts of the leaf. In the typical 

 foliage leaf there are three parts, the 

 expanded portion, or blade 

 (lamina), the leafstalk 

 (petiole), and a pair of ap- 

 pendages at the base of the 



FIG. 89. Leaf of apple, petiole known as stipules. 

 with stipules Many leaves have no 



After Thome petiole and are said to be 



sessile (meaning sitting). Others have no blade 

 and perform their functions as foliage by means 

 of a flattened petiole or large stipules. Most p IG . 90. 

 leaves are bilaterally symmetrical ; that is, they 

 have a right and a left half, which, if folded 

 together along the middle line of the leaf, would 

 nearly coincide. Usually the upper and the under surface differ 

 from each other in color, smoothness, and other respects. 



88 



Leaf of 

 pansy, with leaf- 

 like stipules 



After Decaisne 



