234 TEXTBOOK OF BOTANY 



bell, for example, has root leaves with rounded, almost 

 circular blades, but its upper leaves are long and very narrow. 

 There are some water plants that bear leaves of one sort 

 under water and leaves of a very different f omi in the air ; 

 this is true, for example, of the yellow water crowfoot and 

 of some of the pondweeds. 



249. Special Kinds of Leaves : Seed Leaves. — Leaves, 

 like stems and branches, adapt themselves to particular 

 kinds of usefulness by taking on special forms, some of 

 which are very different from the forms of ordinary foliage 

 leaves. Most of the special kinds of leaves have already 

 been mentioned in one connection or another. We know, 

 for example, that the sepals, petals, and stamens of a flower 

 are leaves adapted to special purposes, and that the pistil is 

 either one leaf or else composed of two or more leaves united. 

 But in this chapter we shall consider only those leaves that 

 help in some of the vegetative work of the plant. 



Seed leaves are usually different, sometimes very different, 

 from the later-formed foliage leaves of the same plant. If 

 the later leaves are divided, the seed leaves are likely to be 

 simpler in outline ; very frequently they are undivided, with 

 entire margins, as is the case in the bean. Some seed leaves 

 become green and for a time do the work of foliage leaves ; 

 this is true of the seed leaves of the squash. On the other 

 hand, the single seed leaf of grasses, including the com, is an 

 absorbing organ which never gets outside the seed coat and 

 never serves as a foliage leaf. In many seeds, such as those 

 of the squash, the oak, and the bean, most of the reserve 

 food is stored in the seed leaves, which therefore in such 

 cases are very thick. Thus seed leaves serve a A-ariety of 

 different purposes in different cases. 



250. Scale Leaves and Bracts. — We have found that 

 scale leaves are borne by many plants — covering mnter 

 buds, growing on underground stems, bulbs, and tubers, 

 or on ordinary shoots, such as those of the pine and the 



