LECT. IX.] LEAVES. 501 



f. The surface of a leaf comprehends both the 

 upper and the under disks. In general, the upper 

 disk is smoother than the under disk ; for, although 

 the vascular fasciculi can be traced in the form 

 of white or coloured lines on the upper, yet, they 

 very rarely produce those elevated ridges which 

 mark their course on the under disk. In treating 

 of the different characters that distinguish the 

 surfaces of leaves, the upper disk only is alluded to. 

 It is necessary to state that the greater number of 

 the following terms are equally applicable to the 

 surface of the stem as to that of the leaf, when the 

 contrary is not expressed. 



The surface of a leaf which exhibits no in- 

 equalities is said to be flat (plana vel lasvis) ; if 

 there be no hairs nor spines, it is smooth (glabra, 

 nuda); and if no fasciculi of vessels be apparent on 

 it, veinless (aveniaj. If it be smooth and shined, 

 it is termed polished (nitida); and lucid (lucidaj, 

 if it be so considerable as to present the appearance 

 of being varnished. If the upper surface be con- 

 vex and the under concave, the leaf is termed 

 convex (convexum); and the opposite of this 

 state, concave (concavum) . Both these states are 

 the consequence of a tightness of the margin. 

 When an oblong or a linear leaf is longitudinally 

 hollowed, and a transverse section of it is a se- 

 micircle, the surface is said to be channelled (ca- 

 naliculata) , 52, (p. 503); but when the transverse 



KK3 



