THE LEAVES. 12? 



the large vein and end free (fig. 149). In the first type the 

 finest branches of the veins, too delicate to be seen without 

 the microscope, often end free in the meshes formed by the 

 next larger branches (fig. 164). Near the margin of a blade 



Fig. 150. Fig. 151. 



Fig. 150.— Parallel venation of leaf of Polygonatum lati/olium. Natural size.— 

 After Ettingshausen. 



Fig. 151.— Pinnately netted venation of leaf of a willow. Natural size.— After Ettings- 

 hausen. 



the larger veins are often so connected with each other as to 

 form one or more series of arches whose convex side is 

 directed toward the margin. These form a sort of selvedge 

 and protect the leaf against tearing (fig. 153). 



