LEAVES 7 



remains. The vein-system or venation of leaves is ex- 

 ceedingly diverse, but all forms can be referred to a few 

 general plans. 



In some leaves a single very prominent vein runs through 

 the middle of the blade, and is called the midrib. From 

 this all the minor veins arise as branches, and such a leaf is 

 said to be pinnately veined (Fig. 2, A, and Fig. 9). In other 

 leaves several large veins (ribs) of equal prominence enter 

 the blade and diverge, each giving rise to smaller branches. 



FIG. 2. Venation: A, pinnately veined leaf of quince, showing blade, petiole, 

 and stipules ; /?, palmately veined leaf of geranium ; C, parallel-veined leaf of 

 lily-of-the-valley. After GRAY. 



Such a leaf is said to be palmately veined (Fig. 2, B, and Fig. 

 16). In still other leaves all the visible veins run ap- 

 proximately parallel from the base of the blade to its apex, 

 such leaves being parallel-veined (Fig. 2, C), as distinct from 

 the two preceding, which are both net-veined. 



1 1 . Form. The forms of leaves are exceedingly varied 

 and are related to their venation. Palmately veined leaves 



