270 ON THE IRRITABILITY OF VEGETABLES. 



traction follows, although the foreign body is not brought 



into contact with all the hairs. 



Apparent mis- This last conclusion is contrary to what is mentioned by 



take of Roth. n - __ ._ . . . \ ,, J . 



Koth. He says, u it the insect be a small one, sometimes 



" only one edge of the leaf is folded up." Hence it should 



seem necessary, that the insect should stir all the hairs of the 



leaf. 



Emptying the In the experiments mentioned no insect or any other 



cause w" the^ b 0( ty absorbs the fluid, and of course the vessels of the leaf 



contraction. cannot be emptied, which is completely in opposition to 



Broiissonnet's theory. 

 Sennebier's We shall next quote Sennebier's own opinion with regard 



iypo lesis. j Q j.jjg con traction of the leaves of the droserse. He says ; 

 " The hairs of the flowers" (he certainly means leaves) " of 

 " the droserse are put in motion by a hair, a needle, an ant, 

 " or small bit of wood. It appears then, that the pressure 

 " alone is the cause of it, and this effect permits us to 

 " ascribe it to a cause purely mechanical*." 

 His facts true J am willing to agree with the first part of this sentence, 

 but from the latter 1 must entirely dissent. Sennebier 

 seems sensible, that the contractions of the leaves take 

 place even when light bodies are placed upon them, which 

 of itself would even lead us to suspect, that pressure is not 

 alone the cause. I know, that, if we press on the centre of 

 the leaf with a pin &c, we may cause its margin to approxi- 

 mate the pin; and this certainly would be owing to a me- 

 chanical cause. But suppose we see the contraction take 

 place, as 1 have done, when a body specifically lighter tkan 

 the leaf itself is placed in the centre, as a bit of rotten wood ; 

 should we be still inclined to ascribe it to a mechanical 

 * cause ? Admit that it is the case. Suppose then we place 

 the same bit of wood on the margin of the leaf, what effect 

 ought to follow ? If it was owing to a mechanical cause, or 

 the weight of the forcing body, as in the last mentioned 

 case, then we should expect, that the part of the margin of 

 the leaf, on which the bit of wood rested, would be depress- 

 ed ; which undoubtedly is not the case, but on the contrary 

 the margin rises, and then contracts toward the foreign 



* Thysiol. Veg. tome V, p. 104. 



bodv, 



