38 OBGANOGBAPHY. 



petioles, as in the Rose and Clover, they are said to be 



adnata (Fig. 73, stip). The stipules of the Tulip-tree 

 serve as bud-^scales, falling ofT soon after the leaves unfold. 

 44. In the Dock and the Buckwheat family the 

 stipules unite and form a sheath around 

 the stem (Fig. 82), which is called Ochrea. 

 If the outer margins only unite, as in the 

 Buttonwood, a double stipule opposite the 

 leaf is formed. If the inner 

 margin only unite, as in the 

 Pondweed (Potamogeton), the 

 double stipule is situated in the 

 axil of the leaf The sheaths 

 of the grasses represent the 

 : petiole, for they bear the blade 

 at their summit; but the small appen- 

 dages, commonly found at the top of the 

 sheath, called a ligule (Fig. 83), is of the 

 nature of a stipule. 



Fig. 80. Spinous stipules (si. siifi) of the Locust. Fig. 81. Tendril stipules of 

 Smilax. Fig. 82. An Ochrea, or Sheathing stipule, of Polygonum. Fig. 83. Grass 

 leaf, with the ligule {liff) representing a stipule. 



