Oy THE STIPHLEB. 



61 



margins outrun the petioles, and extend down the stem, making that 

 winged or alate also. Such leaves are said to be decurrent (decurro, 

 run down). Ex. Mullein. 



245. The amplexicaul or stem-clasping petiole is dilated at the 

 base into a margin which surrounds or clasps the stem, as in the 

 umbilifers. 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. 



246. 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. 



OF THE STIPULES. 



247. Stipules are certain leaf-like expansions, always in paire, 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 kaC, 

 sometimes they are colored like the stem, often they are membranous 

 and colorless. In the palmetto its substance is a coarse net-work re- 

 sembling canvass. 



100 101 



100, Rose leaf, odil-plnnati;, with ndnatc slipulcs. IQl, Violet, (V. tricoloi-), witli simple leaf 

 {l\ and froo compound stipules. 



248. Stipules abb 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. 



249. An ochrea is a membranous sheath inclosing the stem from 

 the node ■ upwards, as in the knot-grass family (Polygonacefe). It is 

 formed of the two stipules cohering by their two margins. In case the 

 two stipules cohere by their outer margin only, a double stipule is 

 formed opposite to the leaf, as in the button-wood. If they cohere by 

 their inner margin, the double stipule appears in the leaf axil, as in the 

 pond-weed (Potamogeton). 



