STUDIES OF SEED-PLANTS 



193 



of common barberry and notice gradations between the 

 spiny leaves and the prickles. Also notice that buds are in 

 the axils of the spines, and compare with 

 the position of buds with reference to leaves 

 ( 157). 



Stipules of Leaves. These are often 

 absent, and when present are variously 

 modified. Compare those of leaves of 

 clover, pea, rose, India rubber tree, buck- 

 wheat. In some plants (e.g., pansy) the 

 stipules are so large that they are not easily 

 distinguished from leaves. The outside 

 bud-scales in beech, tulip-tree, and mag- 

 nolia are stipules. The prickles at base of 

 leaves of black locust tree are obviously 

 modified stipules (Fig. 60). 



Scale-leaves. This name is applied to 

 the small scale-like structures which do not have the usual 

 functions of leaves, but which are chiefly for protection in 

 bulbs and buds. The inner scales of the horse-chestnut bud 

 have a structure which suggests that scale-leaves are modi- 

 fied or reduced leaves. The structures 

 termed bracts which are at the base of 

 flower-stalks (e.g., the petal-like bracts of 

 the clusters of dogwood flowers and the 

 sepal-like bracts on the hepatica flowers) 

 are of similar origin. 



184. The Parts of a Leaf. In the study 

 of the bean leaf, the petiole, blade, and 

 FIG. 60. The spines stipules were mentioned as the parts of a 

 ole J of e a b^aVk typical leaf; but many leaves have some 

 locust leaf are of these parts lacking. Especially are 



modified stipules. 



to. 59. The leaf 

 of yellow vetch is 

 reduced to a ten- 

 dril (6), while the 

 two stipules (n) 

 are large and serve 

 as leaves. 



tinguish between petiole and blade (grasses, lilies, etc.), and 

 leaves of many species of plants have no stipules. 



