INSECTIVOROUS AND CLIMBING PLANTS: 313 



toward the centre of the leaf; and this also takes 

 place, as we have seen, when an exciting object is 

 lodged at the centre. But when the object is placed- 

 upon either half of the leaf, the impulse radiating 

 thence causes all the surrounding untouched ten- 

 tacles to bend with precision toward the point of 

 excitement, even the central tentacles, which are mo- 

 tionless when themselves charged, now responding 

 to the call. The inflection which follows mechanical 

 irritation or the presence of any inorganic or insoluble 

 body is transient ; that which follows the application 

 of organic matter lasts longer, more or less, according 

 to its nature and the amount ; but sooner or later the 

 tentacles resume their former position, their glands 

 glisten anew with fresh secretion, and they are ready 

 to act again. 



As to how the impulse is originated and propa- 

 gated, and how the movements are made, compara- 

 tively simple as the structure is, we know as little as 

 we do of the nature of nervous impulse and muscular 

 motion. But two things Mr. Darwin has wellnigh 

 made out, both of them by means and observations 

 so simple and direct as to command our confidence, 

 although they are contrary to the prevalent teaching. 

 First, the transmission is through the ordinary cellular 

 tissue, and not through what are called the fibrous or 

 vascular bundles. Second, the movement is a vital 

 one, and is effected by contraction on the side toward 

 which the bending takes place, rather than by tur- 

 gescent tension of the opposite side. The tentacle is 

 pulled over rather than pushed over. So far all ac- 

 cords with muscular action. 



