254 DliOSERA EOTUNDIFOLIA. Chap. 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 moA^ement 

 is great. Fully expanded tentacles in becoming in- 

 flected sweep through an angle of 180^; and if they 

 are beforehand reflexed, as often occurs, tile 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 afi'ected ; 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 



