66 



DESCRIPTIVE BOTANY. 



midrib, but the vessels diverge in two strong lateral 

 nerves, from which branches are 

 given off, on that side only which is 

 towards the apex of the leaf (fig. 60.). 

 This form of nervation is far less com- 

 mon than either of the preceding. The 

 pedate leaves are thus nerved. 



(73.) Curvinerved Leaves. In 

 these leaves, the nerves are more or 

 less curved at their base, or point 

 whence they diverge ; and they retain 

 a certain parallelism among them- 

 selves, as well as a simplicity of 

 structure, which very readily distin- 

 guishes them from the angulinerved 

 leaves. This mode of nervation may 

 be subdivided into two classes. 



(a.) Convergent. Where several 

 nerves, curved at the base of the 

 limb, run nearly parallel to its margins, and proceed 

 gradually converging towards its apex 

 (fig- 6l.). 



(b.) Divergent. Where the ves- 

 sels collectively form a midrib to 

 the limb, and numerous simple nerves 

 diverge from it in a pinnate manner, 

 but maintain nearly a parallel, or some- 

 what curvilinear course (fig. 62.). 



(74.) Forms of Leaves. It will 

 easily be understood, how very much 

 varied the forms of leaves may be- 

 come. Their contour is principally 

 determined, by the distance to which the 

 ramifications of the nerves extend ; 

 and the shape of the margin is modi- 

 fied, by the degree to which the paren- 

 chyma is developed between them. 

 Thus, in ovate leaves (fig. 63.), the 

 margin of a, which is only slightly indented, is said to 



