THEIR STRUCTURE AND FORMS. 



105 



base, as in many umbelliferous plants ; sometimes it forms a 

 sheath, occasionally it is bordered with appendages, &c. Peti- 

 oles may assume special functions, to be hereafter considered. 

 The woody and A^ascular tissue runs lengthwise through the 

 petiole, in the form usually of a definite number of parallel 

 threads, to be ramified in the blade. The ends of these threads 

 are apparent on the base of the leafstalk when it falls off, and on 

 the scar left on the stem, as so many round dots (Fig. 81, 85, 

 91), of a uniform number and arrangement in each species. 



203. Partial Petioles are the divisions of the petiole in a 

 compound leaf. The footstalk of a leaflet takes the diminutive 

 name of PETIOLULE. 



204. Stipules (157) are lateral appendages, one each side of 

 the base of the petiole, sometimes free 



from it and from each other (Fig. 



142), sometimes attached by one 



edge to its base (Fig. 211), some- 



times united with each other into a 



single body (Fig. 212) in various 



ways or degrees. In the latter case, 



they usually appear to be within the 



base of the leaf or leafstalk ; or, as 



in the Plane-tree, they may be joined 



into one over against the leaf, as 



if opposite to it, but their normal 



position is supposed to be lateral or 



marginal to the petiole. Sometimes 



they are foliaceous in appearance and 



in function ; sometimes they are dry 



and colorless or scale-like, reduced to 



mere epidermal tissue, and evidently 



functionless ; sometimes (as in Mag- 



nolia, Fig. 81, Fig-tree, and Beech), 



they serve as bud-scales, and fall when 



the leaves develop ; sometimes the}' are 



reduced to a mere bristle, or take the 2 n 212 



form of a spine, as in the Locust (Robinia). Between salient 



expansions or wing-like margins of tli3 base of the petiole, 



such as those of the Saxifrage tribe, and stipules adnate to the 



margins of the petiole, as in most Rosacea?, there is no clear 



limitation. But presence or absence of stipules generally runs 



FIG. 2H. Clover-leaf, with adnate stipules. 212. Odireate stipules (ochrea or 

 of Polygonum orientale, sheathing the stem for some distance, and ending in a spread- 

 ing border. 



