LEAVES 



135 



he can hardly fail to notice that there is a general relation 

 between the plan of venation and the shape of the leaf. 

 How maiy this relation be stated? In most cases the 

 principal veins follow at the outset a pretty straight 

 course, a fact for which the student ought to be able to 

 give a reason after he has performed Exp. XXXII. 



On the whole, the arrangement of the 

 veins seems to be 

 such as to stiff- 

 en the leaf 

 most in the 

 parts that need 



Fig. 97. — PaJmately Divided 

 Leaf of Buttercup. 



Fig. 98.— Leaf of Ap- 

 ple, with Stipules. 



Fig. 99. — Leaf of 

 Pansy, with Leaf- 

 Like Stipules. 



most support, and to reach the region near the margin by 

 as short a course as possible from the end of the petiole. 



144. Stipules. — Although they are absent from many 

 leaves, and disappear early from others, stipules form a 

 part of what the botanist regards as an ideal or model 

 leaf.^ When present they are sometimes found as little 



1 Unless the elm twigs used in the previous study were cut soon after the 

 unfolding of the leaves in spring, the stipules may not have been left in any 

 recognizable shape. 



