92 



STRUCTURAL BOTANY. 



alette, also. Such leaves are said to be decurrent (decurro, run 

 down). Ex., Mullein. 



275. The amplexicaul petiole is dilated at the base into a 

 margin which surrounds or clasps the stem, as in the Umbelli- 

 fcrs. 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 (petio- 

 lules) 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, sup- 

 ported by as many branches of a compound petiole. 



277. Stipules are certain leaf-like expansions, always 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 usually resemble the leaf; sometimes they are colored like 

 the stem, often they are membranous and colorless. In the 

 Palmetto its substance is a coarse net- work resembling canvas. 



301, BOM lent', cud-pinnate, with aunate stipules. 302. Violet (V. tricolor), with simple leaf (I), and free 



compound stipules. 



278. Stipules are often adnate, or adherent to the petiole, as in 

 the Rose ; more generally they are free, as in the Pea and 

 Pansy. In these cases and others they act the part of leaves ; 

 again they are very small and inconspicuous. 



279. An Ochrea is a membranous sheath enclosing the stem 

 from the node iipward, as in the Knot-grass family (Polygo- 

 nacese). It is formed of the two stipules cohering by their two 

 margins. In case the two stipules cohere by their outer margin 



