206 DROSERA ROTUNDIFOLIA. [Chap. X. 



ing passed so quickly down one of the extreme marginal 

 tentacles (about iV of an inch in length), should never, as 

 far as I have seen, aflfect the adjoining tentacles, I do not 

 understand. It may be in part accounted for by much 

 energy being expended in the rapidity of the transmission. 



Most of the cells of the disc, both the superficial ones and 

 the larger cells which form the five or six underlying layers, 

 are about four times as long as broad. They are arranged 

 almost longitudinally, radiating from the footstalk. The 

 motor impulse, therefore, when transmitted across the disc, 

 has to cross nearly four times as many cell- walls as when 

 transmitted in a longitudinal direction, and would conse- 

 quently be much delayed in the former case. The cells of 

 the disc converge towards the bases of the tentacles, and are 

 thus fitted to convey the motor impulse to them from all 

 sides. On the whole, the arrangement and shape of the cells, 

 both those of the disc and tentacles, throw much light on 

 the rate and manner of diffusion of the motor impulse. But 

 why the impulse proceeding from the glands of the exterior 

 rows of tentacles tends to travel laterally and towards the 

 centre of the leaf, but not centrifugally, is by no means 

 clear. 



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 inflected tentacle, which was somewhat thinner than the 

 bristle. The amount or extent, also, of the movement is 

 great. Fully expanded tentacles in becoming inflected 

 sweep through an angle of 180** ; and if they are beforehand 

 reflected, 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 



