no 



BOTANY AND PHARMACOGNOSY. 



the distribution of the veins in this manner produces a lamina 

 with an even, or entire margin, and such a system of venation is 

 known as a closed system of venation. The leaves of Veratrum 

 (Fig. 129) and Zea Mays, furnish other examples of parallel- 

 nerved leaves. 



In palms (Fig. 251) the venation is somewhat different. The 

 veins instead of converging toward the apex as they do in the 

 more or less lanceolate leaf of lily-of-the valley, radiate from the 

 base to the margin of the more or less round leaf, and a leaf of 

 this type is said to be palmi-nerved. 



Fig. 72. Chinquapin (Castanea pu»tila). A, branch with long aments of staminate 

 flowers; B, fruiting branch bearing alternate, exstipulate and pinnate, reticulately-veined 

 leaves. The leaves are elliptical in general outline, acute at both apex and base, and with 

 sharply serrate margins. 



There is still a third type of venation in Monocotyledons. 

 In this instance one principal vein runs from the base to the apex 

 of the leaf, and from this branches run parallel to the margin. 

 The banana furnishes an example of this type, and is said to be 



PINNI-NERVED. 



Venation in Dicotyledons. — Here the veins are charac- 

 terized by their habit of repeatedly branching and anastomosing. 



