108 STRUCTURAL BOTANY. [92. 



275. The amplexicaul petiole is dilated at the base 

 into a margin which surrounds or clasps the stem, as 

 in the Umbellifers. Frequently we find the stem- 

 clasping margins largely developed, constituting a 

 sheath with free edges in the Grasses, or closed into 

 a tube in the Sedges. 



276. The petiole is simple in the simple leaf, but 

 compound or branched in the compound leaf, with as 

 many branches (petiolules) as there are divisions of 

 the lamina. A leaf is simple when its blade consists 

 of a single piece, however cut, cleft, or divided ; and 

 compound when it consists of several distinct blades, 

 supported by as many branches of a compound petiole. 



301, Rose leaf, odd-pinnate, witb adnate stipules. 302, Violet (V. tricolor), with simple leaf (I), and free 



compound stipules. 



277. Stipules are certain leaf-like expansions, al- 

 ways in pairs, situated one on each side of the petiole 

 near the base. They do not occur in every plant, but 

 are pretty uniformly present in each species of the 

 same natural order. In substance and color they usu- 

 ally resemble the leaf ; sometimes they are colored like 

 the stem, often they are membranous and colorless. 

 In the Palmetto the leaf-base is a coarse net-work 

 resembling canvas. 



278. Stipules are often adnate, or adherent to the 

 petiole, as in the Rose ; more generally they are free, 



