Leaves and Their Structures 



23 



the apex or outer end of the leaf and gradually become larger 

 toward the base of the blade. They continue down through the 

 petiole, or leafstalk, into the interior of the stem. 



Fig. 10. Divided and compound leaves: A, buckeye; B, oxalis; C, avens; D, celandine; 

 E, cliff fern ; F, dandelion. 



At the base of the petiole there is in many leaves a pair of small 

 appendages, the stipules (Fig. 9) . These are usually unimportant 

 structures, but occasionally, as in the pansy and garden pea, 

 they are large and blade-like. These enlarged stipules supple- 

 ment the blade, or in some plants may even take its place in food 

 manufacture. The primary divisions of the leaf are the blade, the 

 petiole, and the stipules. 



The leaves of many grass-like plants have no petioles or stip- 

 ules. In such plants the blade is attached to the stem by a 

 sheath, which may be long or short. At the top of the sheath is a 

 short, collar-like extension called the ligule. In the bamboo the 

 ligule consists of several long bristles. 



When the blade of a leaf is attached directly to the stem with- 

 out an intervening petiole, it is said to be sessile (Latin : sedere, 

 to sit). 



Compound leaves. When several blades are attached to a 

 single petiole, as in clover, buckeye, walnut, ash, and hickory, the 

 leaf is called a compound leaf. The blades of the compound leaf 

 are called leaflets. There is usually a distinct joint between the 



