28 



THE LEAF 



31. Parts of the Leaf. — Examine a young, healthy leaf 

 of apple, quince, elm, etc., 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 

 bristlelike bodies at the base, known 

 as stipules. Make a sketch of any leaf 

 provided with all these parts and label 

 them respectively blade, petiole, and 

 stipules. 



Ti. — A typical leaf and 

 its parts : d, blade ; p, peti- 

 ole ; J, J, stipules. 



-Spiny stipules 

 of Clotbur. 



32. Stipules. — These 

 three parts make up a 

 perfect or typical leaf, but as a matter of 

 fact, one or more of them is usually want- 

 ing. The office of stipules, when present, 

 is generally to subserve 

 in some way the pur- 

 poses of protection. In 

 many cases, as the fig, ^^■ 

 elm, beech, oak, magno- 

 lia, etc., they appear only as protective 

 scales that cover the bud during winter, 

 and fall away as soon as the leaf ex- 

 pands. When persistent, that is, en- 

 during, they sometimes take the form 

 of spines and thorns, as in the black 

 locust and spiny clotbur {Xanthium 

 spinosum). The sheathing stipules of 

 the smartweeds and bindweeds (^Polygo- 

 num) serve to strengthen the stem at the joints (Fig. 13), 

 and the adnate stipules (Fig. 14) of the rose, clover, 

 strawberry, etc., may serve either as water holders or 

 as shields against climbing insects. In the smilax and 

 some other vines they appear as tendrils for climbing, 

 while in other cases, as the garden pea and pansy, they 

 become large and leaflike, or may even usurp the place of 



13. — Sheathing stipules 

 of " prince's feather " {^Po- 

 lygonum orientate) (Gray) . 



