LEAVES hoo 
he can hardly fail to notice that there is a general relation 
between the plan of venation and the shape of the leaf. 
How may 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 
; Fic. 99. — Leaf of 
Fic. 97.— Palmately Divided FiG. 98.— Leaf of Ap- Pansy, with Leaf- 
Leaf of Buttercup. ple, with Stipules. 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.1 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. 
