70 



MORPHOLOGY OF LEAVES AS FOLIAGE. [LESSON 9. 



afterwards, as in the Tulip-tree. In the Pea the stipules make a 

 very conspicuous part of the leaf; while in the Bean they are quite 

 small ; and in the Locust they are reduced to bristles or prickles. 

 Sometimes the stipules are separate and distinct (Fig. 83): often 

 they are united with the base of the leaf-stalk, as in the Rose and 

 the Clover (Fig. 136) : and sometimes they grow together by both 

 margins, so as to form a sheath around the stem, above the leaf, as 

 in the Buttonwood, the Dock, and almost all the plants of the 

 Polygonum Family (Fig. 137). 



179. The sheaths of Grasses bear the blade on their summit, and 

 therefore represent a form of the petiole. The small and thin ap- 

 pendage which is commonly found at the top of the sheath (called a 

 ligule) here answers to the stipule. 



FIG. 138. Ternately -decompound leaf of Meadow Rue (Thalictrum Cornuti). 



