Guar. 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, 24 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 Dionza and of 
