642 CONSERVATIVE ORGANS, [LECT. XI. 



1. The awl-shaped bristle (seta subulata) is the 

 most common of the simple bristles : it is slightly 

 curved, and gradually tapering from the base to 

 the apex (Plate 9, fig. 18), which is rigid and very 

 sharp. These bristles, when they all incline in 

 the same direction, produce the scabrous charac- 

 ter of some leaves, which is perceived when the 

 hand is passed lightly over their surface, from the 

 apex towards the base; as exemplified in those 

 of Symphytum orientate, and many other plants. 

 A variety of the subulate bristle, found on the 

 stem and branches of the Sensitive Plant, Mimosa 

 sensitiva, is barbed on its sides (Plate 9, fig. 19) ; 

 and another variety, as exemplified on the leaves 

 of Borage, Borago officinalis, is seated on a ve- 

 sicular tubercle (ib. fig. 20), containing a fluid, 

 which is ejected through the bristle when it is 

 compressed so as to wound the finger; and which, 

 being left in the wound, excites a slight degree of 

 inflammation in the part. But the sting of the 

 Nettle is the best example of this form of bristle, 

 when it is an excretory duct of a gland ; and it 

 has, not inaptly, been compared to the fang of 

 a serpent. Its structure has been known since 

 the time of Hook, who first described it *. It con- 

 sists of two distinct parts: one, to employ Hook's 

 language, "like a bodkin, very hard and stiff, 



* Micographia, p. 142. 



