sx 



BOTANT. 



general aud particular outlines of tlie blade. There is commonly 

 a mid-vein (midrib) running centrally from base to apex, and 

 secondary ones which run centrally (or near}y so) through the 

 lobes. We have thus a, pinnate venation, in pinnately-lobed leaves, 

 and radiate venation, in radiately-lobed leaves. Moreover, a 

 modified form of the pinnate or the rarliate venation usually 

 occurs in leaves which are not lobed. In grasses, sedges, and 

 many other Monocotyledons the venation is longitudinal. (Fig. 

 XVII.) 



The leaves of most Monocotyledons have their principal as well 

 as subsidiary veins more or less parallel, while in Dicotyledons the 



LON 



,NAL. 



Fig. XVII.— Diagrams sbowing principal kinds of venation. 



subsidiary veins are mostly disposed in a net-like manner; the 

 former are hence caWeA. parallel-veined, and the \sAtev netted'odned, 

 leaves. 



Size of the Blade. — The length and width of a blade of average 

 size should be measured, and when there is great diversity in size 

 the extremes should also be noted. 



Surface of the Blade. — The principal varieties of surface are 

 the following: 



1. Smooth, when there are no sensible projections or depressions, 

 as hairs, warts, pits, etc., upon the surface. Sometimes a smooth 

 surface is shining; in some cases (e.g., the cabbage) it is covered 

 with a fine whitish, floury substance (bloom), and is then said to 

 be glaucous. 



