LEAVES AND THEIR USES 



229 



245. Parts of a Leaf (Fig. 138). — Most foliage leaves, 

 like those of the cucumber, are more or less clearly divided 

 into a leaf -stalk and a blade. Sometimes, as in the case of 

 the dandelion, the blade narrows gradually into the stalk, so 

 that we cannot say just where one ends and the other begins. 

 Some leaves, like those of most lilies, have no stalk at all ; 

 the blade is attached directly to the stem or branch of the 

 plant. We have seen that the lower 

 part of the leaf of the Indian corn 

 forms a sheath that surrounds the stem 

 for some distance. Such sheathing 

 leaves are characteristic of the mem- 

 bers of the grass family ; but they are 

 found in many plants of other families 

 as well. 



Many leaves have stiptdes. Some 

 stipules, like those of the bean, are 

 small ; but some, as in the pansy and 

 the pea, are so large that they may 

 easily be taken for separate leaves. In 

 any case, the stipules are really parts 

 of the leaf to which they are attached. 

 Compound leaves, like those of the 

 bean, sometimes also have small stipule- 

 like attachments at the base of the 

 stalk of each leaflet in addition to the 

 stipules at the base of the leaf-stalk. 



Usually both the leaf -stalk and the shoot (stem or branch) 

 are thickened slightly at or near the point where the leaf- 

 stalk is attached to the shoot. These two thickenings often 

 run together so that we cannot distinguish just where the 

 leaf -stalk ends and the tissues of the shoot begin. In many 

 of the plants of the pulse family (including peas, beans, and 

 clover) the thickening of the base of the leaf -stalk is especially 

 marked. 



Fig. 138. — The leaf 

 of a rose — a pinnately 

 divided leaf with stip- 

 ules. The leaflets are 

 toothed. 



