SECTION 7.] 



THEIR ARRANGEMENT. 



67 



Clover (Fig. 177), they are adnate. Wlieu the two stipules unite and 

 sheathe the stem above the insertion, as in Polygonum (Fig. 178), this 

 sheath is called an Ocrea, from its likeness to a greave or leggiu. 



177. In Grasses, when tlie sheathing base of the leaf may answer to 

 petiole, the summit of the sheath commonly projects as a thin and short 

 membrane, like an ocrea : this is called a Ligula or Ligule. 



178. When stipules are green and leaf-like they act as so much foliage. 

 In the Pea they make up no small part of the actual foliage. In a related 

 plant (Lathyrus Aphaca, Fig. 173), they make the whole of it, the remainder 

 of the leaf being tendril. 



179. In m^ny trees the stipules are the bud-scales, as in the Beech, and 

 very conspicuously in the Fig-tree, Tulip-tree, and Magnolia (Fig. 179). 

 These fall off as the leaves unfold. 



180. The stipules are spines or prickles in Locust and several other 

 Leguminous trees and shrubs ; they are tendrils in Smilax or Greenbrier. 



§ 4. THE ARRANGEMENT OF LEAVES. 



181. Phyllotaxy, meaning leaf-arrangement, is the study of the position 

 of leaves, or parts answering to leaves, upon the stem. 



182. The technical name for the attachment of leaves to the stem is 



the insertion. Leaves (as already noticed, 54) are inserted in three modes. 

 They" are 



Alternate (Fig. 181), that is, one after another, or in other words, with 

 only a single leaf to each node ; 



Fig. 181. Alternate leaves, in Linden, Lime-tree, or Basswood. 

 Fig. 182. Opposite leaves, in Red Maple. 



