98 



THE LEAVES OF PLANTS. 



thence the figure necessarily changes. Thus, when it is much greater than that of a 

 serrate leaf, the leaf exhibits a series of lateral prolongations or lesser leaves, the 

 tttached end of which is yet distant from the midrib, and the whole is termed pmnatifd 

 (Fig. 164). In other instances the arrest of development is equally great at certain 

 points with the pinnatifid leaf, but is not so universal ; and thence a lyre-shaped or 

 halberd-head shape results, as in Figs. 166 and 167. 



In all these examples the longitudinal system of development is perfect, and the 

 lateral deficiency is so arranged that the edge of the dentation is entire ; but in many 

 cases the latter is so modified that the dentations are themselves dentated or serrated. 

 Such leaves are known as doubly-serrated (Fig. 163), and doubly-pinnatifid (Fig. 165). 

 When the longitudinal system is modified, at the same time that the transverse develop- 

 ment is restricted, the leaf puts on a lobed character. Such is represented in Figures 



Fig. 168. Fig. 169. 



Fig. 168. An angular-lobed leaf. 



Fig. 169. An orbicular-lobed crenate leaf. 



Fig. 170. A palmate or deeply-divided lobed leaf. 



Fig. 170. 



168 and 169, in both of which the modification is hut slightly evident; but in others 

 the division of the lobes is so great that the line of separation passes nearly to the 

 petiole, as in the palmate leaf shown in Fig. 170, and quite to the petiole and primary 

 veins in the "Water Crowfoot (Ranumnlus aqwtilis). 



It is not necessary that we should enter minutely into the mode of development of 



every variety of leaf ; and it is probable that we 

 have alfeady given such examples as will enable 

 the reader to apply the principles now enunciated 

 to any other form which may present itself. 

 "We shall therefore only 

 name a few other forms 

 which are not unsusally 

 met with. The reniform 

 or kidney-shaped leaf is 

 represented in Fig. 172 ; 

 cordate or heart-shaped, 

 and sagittate or arrow- 

 shaped (Fig. 173). 



Leaves are, for the most part, developed sym- 

 metricallythat is, each half closely resembles 

 the other ; but in some instances this rule is not 

 observed. Thus in the Begonia the leaf is mani- 

 festly unsymmetrical, having one side far less developed than the other ; and in some 



Fip. 172. Reniform or 

 kidney-shaped leaf. 



Fig. 173. Arrow-headed leaf of the 

 SAOITTARIA (Sagittce folia). 



