254 DROSERA ROTUNDIFOLIA, Cuap. X. 
Mechanism of the Movements, and Nature of the 
Motor Impulse—Whatever may be the means of 
movement, the exterior tentacles, considering their 
delicacy, are inflected with much force. A bristle, 
held so that a length of 1 inch projected from a 
handle, yielded when I tried to lift with it an in- 
flected tentacle, which was somewhat thinner than the 
bristle. The amount or extent, also, of the movement 
is great. Fully expanded tentacles in becoming in- 
flected sweep through an angle of 180°; and if they 
are beforehand reflexed, as often occurs, the angle is 
considerably greater. It is probably the superficial 
cells at the bending place which chiefly or exclusively 
contract; for the interior cells have very delicate 
walls, and are so few in number that they could hardly 
cause a tentacle to bend with precision to a definite 
point. Though I carefully looked, I could never 
detect any wrinkling of the surface at the bending 
place, even in the case of a tentacle abnormally 
curved into a complete circle, under circumstances 
hereafter to be mentioned. 
All the cells are not acted on, though the motor 
impulse passes through them. When the gland of 
one of the long exterior tentacles is excited, the 
upper cells are not in the least affected; about half- 
way down there is a slight bending, but the chief 
movement is confined to a short space near the base; 
and no part of the inner tentacles bends except the 
basal portion. With respect to the blade of the leaf, 
the motor impulse may be transmitted through many 
cells, from the centre to the circumference, without 
their being in the least affected, or they may be 
strongly acted on and the blade greatly inflected. 
In, the latter case the movement seems to depend 
partly on the strength of the stimulus, and partly on 
