CHAPTER VI. THE LEAF 



I. THE TYPICAL LEAF AND ITS PARTS 



Material. — Leaves of different kinds showing the various modes of 

 attachment, shapes, texture, etc. For stipules, leaves on very young 

 twigs should be selected, as these bodies often fall away soon after the 

 leaves expand. The rose, Japan quince, willow, strawberry, pea, pansy, 

 and young leaves of beech, apple, elm, tulip tree, India rubber tree, 

 magnolia, knotweed, furnish good examples of stipules. For the different 

 orders of leaf arrangement, lilac, maple, spurge, trillium, cleavers (Galium) 

 show the opposite and whorled kinds. Elm, basswood, grasses ; alder, 

 birch, sedges ; peach, apple, cherry, show respectively for each group the 

 three principal orders of alternate arrangement. 



165. Parts of the leaf. — Examine a young, healthy leaf 

 of apple, quince, or elm, as it stands upon the stem, and 

 notice that it consists of three parts : a 

 broad expansion called the blade; a leaf 

 stalk or petiole that attaches it to the 

 stem ; and two little leaflike or bristle-like 

 bodies at the base, known 

 as stipules. Make a 

 sketch of any leaf pro- 

 vided with all these parts, 

 and label them, respec- 

 tively, blade, petiole, and 

 stipules. These three parts make up a per- 

 fect or typical leaf, but as a matter of fact, 

 one or more of them is usually wanting. 



166. Stipules. — The office of stipules, 

 when present, is generally to subserve in 

 some way the purposes of protection. In many cases, as in 

 the fig, elm, beech, oak, magnoHa, etc., they appear only as 

 protective scales that cover the bud during winter, and fall 



147 



Fig. 177.— a typi- 

 cal leaf and its parts: 

 b, blade ; p, petiole ; 

 s, s, stipules. 



Fui. 178. — Spiuy 

 stipules of clotbur. 



