Chap. XIII. SENSITIVENESS OF FILAMENTS. 289 



possible to touch them ever so lightly or quickly 

 with any hard object without causing the lobes to 

 close. A piece of very delicate human hair, 2J inches 

 in length, held dangling over a filament, and swayed 

 to and fro so as to touch it, did not excite any move- 

 ment. But when a 'rather thick cotton thread of the 

 same length was similarly swayed, the lobes closed. 

 Pinches of fine wheaten flour, dropped from a height, 

 produced no effect. The above-mentioned hair was 

 then fixed into a handle, and cut off so that 1 inch 

 projected ; this length being sufficiently rigid to sup- 

 port itself in a nearly horizontal line. The extremity 

 was then brought by a slow movement laterally into 

 contact with the tip of a filament, and the leaf instantly 

 closed. On another occasion two or three touches of 

 the same kind were necessary before any movement 

 ensued. When we consider how flexible a fine hair 

 is, we may form some idea how slight must be the 

 touch given by the extremity of a piece, 1 inch in 

 length, moved slowly. 



Although these filaments are so sensitive to a momen- 

 tary and delicate touch, they are far less sensitive than 

 the glands of Drosera to prolonged pressure. Several 

 times I succeeded in placing on the tip of a filament, 

 by the aid of a needle moved with extreme slowness, 

 bits of rather thick human hair, -and these did not., 

 excite movement, although they were more than ten 

 times as long as those which caused the tentacles of 

 Drosera to bend ; and although in this latter case they 

 were largely supported by the dense secretion. On 

 the other hand, the glands of Drosera may be struck 

 with a needle or any hard object, once, twice, or even 

 thrice, with considerable force, and no movement 

 ensues. This singular difference in the nature of 

 the sensitiveness of the filaments of Dionsea and of 



