354 A TEXT-BOOK OF BOTANY. 



to be villous; or when the hairs cover each other in one direction 

 it is described as sericeous or silky. When the hairs are stiff 

 though slender we speak of a hirsute covering; when the hairs 

 are vernate, thickish and stiff, as in Borago, the surface is spoken 

 of as being hispid. If the hairs are bristle-like the surface is 

 described as strigose; or if they are terminated by a globular, 

 glandular head (Figs. loo, 124), as glandular. Again, when 

 the hairs are matted the surface is described as lanate ; when 

 they are long it is said to be woolly; or when they are short 

 and soft as in Mullein it is said to be tomentose. 



When the hairs are hard and prickle-like the surface is 

 described as hispid or strigose ; when they are modified to spines 

 it is said to be spinose; and when they are hooked it is described 

 as echinate. 



In still other cases the epidermal cells, particularly of leaves, 

 are uneven, forming depressions and protuberances which if 

 slight give the surface the appearance described as rugose ; or if 

 wart-like, give the appearance known as verrucose. Further- 

 more, the veins of leaves may be quite prominent, particularly 

 in the lower surface, and if they are much reticulated in addition, 

 the surface is described as reticulate. 



Texture of Leaves. — Leaves also vary in texture. A thin 

 pliable leaf is called membranous ; one which is thick and leathery, 

 coriaceous ; and one which is thick and fleshy, succulent, as that 

 of the century plant and Aloe (Fig. 130). 



Forms of Leaves. — The leaves of plants exhibit an almost 

 innumerable variety of forms ; even on the same plant there are not 

 infrequently several forms, as in Viola tricolor and sassafras 

 (Fig. 203) ; even the two margins of the same leaf may vary, as in 

 Hamamelis and Begonia, when it is known as an inequilateral 

 or asymmetric leaf. It frequently happens that the lower leaves 

 on a shoot are lobed while the upper ones are entire, or some of 

 the leaves may be sessile and other petiolate. Many of the terms 

 used in ordinary language in describing the forms of objects are 

 applied here also, as linear, lanceolate, oblong, elliptical, spatulate, 

 wedge-shaped, etc. 



Summit of Leaf. — A number of terms are used to describe 

 the summit or apex of the lamina, as acute, when the form is 



