LECT. IX.] LEAVES. 505 



maxim of Linnaeus, " pubescentia ludicra est dif- 

 " ferentia, cum cultura ssepius deponantur *," 

 remarks that " the direction of the hairs or 

 " bristles proves a very sure means of distinguish- 

 " ing species, especially in the genus Mentha, the 

 " hairs about whose calyx and flower-stalk point 

 " differently in different species; and/' he adds, 

 " I have found it the only infallible distinction 

 " between one Mint and another ^." 



The surface of a leaf may be furnished with 

 visible glands. When these are elevated, or on 

 pedicils, the surface is said to be glandular (glan- 

 dulosa) ; but, when they are not raised, they ap- 

 pear like punctures, which either penetrate the 

 substance of the leaf, or are merely superficial and 

 visible on one disk only. In either case the surface 

 is said to be dotted (punctata), 58, (page 503). Any 

 glandular exudation, if considerable on a surface, 

 gives a character and denomination to it: thus, if 

 it be moist and tenacious, the surface is termed 

 viscid (vlscida vel glutinosa) ; it is hoary (pruinata 

 vel incana), if the secretion be a dry, very fine, 

 waxy powder of a bluish colour, devoid of gloss, 

 and easily wiped off; and mealy (farinosa), i it 

 resemble a mealy powder. 



The majority of leaves is green ; and, as has 

 bqen already mentioned, this colour is of a deeper 



* Phil. Bot. 272. f Introd. p. 228. 



