OR APPENDAGES OF PLANTS. 173 



they have often a starry figure. Very generally they 

 'are found, under a microscope, to be curiously 

 jointed. Some Begonice bear on their leaves flat 

 little straps called by authors r amenta, shavings, 

 instead of cylindrical hairs ; but I know not that 

 they at all differ in nature from the usual pubescence, 

 nor do they merit to be particularly distinguished. 

 Some of the natural order of asperifblia, as Echium, 

 t. 181, and Lycopsis, t. 938, especially some exotic 

 species of this order, are clothed with curious white 

 hard tubercles from which their bristles proceed. 

 Echium pyrenaicum, Desfont. Atlant. v. 1. 16'4,is 

 an instance of this, f. 125. 



The pubescence of plants varies greatly in degree 

 according to differences of soil or exposure; several 

 kinds, as Mentha hirsuta, t. 447, 448, naturally 

 hairy, being occasionally found smooth, but if trans- 

 planted they soon resume their proper habit. Yet 

 the direction of the hairs or bristles proves a very 

 sure means of distinguishing species, especially in 

 the genus Mentha, the hairs about whose calyx and 

 flower-stalk point differently in different species, and 

 I have found itthe only infallible distinction between 

 one Mint and another. See Trans, of Linn. Soc. 

 v. 5. 171. The accurate Dr. Roth has lately applied 

 the same test to the species of Myosotis, which all 

 botanists before him had either confounded under 

 M. scorpioides, Engl. Bot. t. 480, or else separated 

 upon vague principles. Some species of Galium 



