90 ELEMENTS OF BOTANY. 
117. 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 bristle-shaped 
objects, at the base of the leaf as in the apple leaf (Fig. 71), 
sometimes as leaf-like bodies, for example in the pansy (Fig. 
72), and in many other forms, one of which is that of spinous 
appendages, as shown in the common locust (Fig. 76). 
118. elation of Venation to Shape of Leaves. — As soon 
as the student begins to observe leaves somewhat widely, 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. 25. 
On the whole the arrangement of the 
veins seems to be such as to stiffen the 
leaf most in the parts that need most 
support, and to reach the region near the 
margin by as short a course as_ possible 
from the end of the petiole. 
119. Parallel-Veined Leaves. — The 
leaves of many great groups of plants, 
such as the lilies, the sedges, and the 
grasses, are commonly parallel-veined, that 
ee At ie is, with the veins running nearly parallel, 
PLES ETS lengthwise through the blade, as shown in 
Fig. 73, or with parallel veins proceeding 
from a midrib and then sending off parallel veinlets, as 
shown in Fig. 74. 
1 Unless the elm twigs used in the previous study were cut soon after the unfold- 
ing of the leaves in spring, the stipules may not have been left in any recognizable 
shape. 
