ON THE IRRITABILITY OF VEGETABLES. g£ft 



** the quickness of this action is then proportional to the 

 «' number of hairs touched by the insect*." 



This theory at first reading does not appear even to be x^ theory 

 plausible; for how is it possible, that an insect can absorb not plausible, 

 a thick tenacious fluid? No doubt however part of this 

 fluid will be attached to the part of the insect which touches 

 it, but this seems quite unconnected with the contraction of 

 the leaf, as I shall immediately show. On the 30th of Jul}' emwithfacis. 

 J brought from rhe country a number of plants of the dro- 

 jjera rotundifolia, and on inspecting them I found many of 

 the hairs deprived of their viscid fluid, but yet both they 

 and the leaf remained quite expanded and in good condi- 

 tion. This appeared to me a favourable opportunity, to 

 ascertain either the accuracy or inaccuracy of ihousonnet's 

 theory. Next day in the afternoon about four o'clock, when 

 rather cloudy and the temperature moderate, I placed a 

 small bit of sulphate of copper in the disk of one of these 

 expanded leaves. Now if Broussonnet's theory was accu- 

 rate, I conceive, no effect should have taken place ; but on 

 the contrary by six o'clock most of the hairs on one side of 

 the leaf, even the outermost, had bent themselves complete- 

 ly over the morsel of sulphate of copper. I have repeated 

 this experiment frequently, and always with the same result. 

 It may be well also to observe, that in other experiments 

 the sulphate of copper rested upon some of the small hairs 

 in the disk of the leaf without touching the leaf itself, yet 

 the bending of the hairs and leaf was complete. In some 

 plants also, in which every hair of the leaf has been covered 

 with a drop of viscid fluid, I cautiously placed a small bit 

 of bread, or wood, on three or four of the central hairs with- 

 out touching the other hairs, or the viscid fluid on their 

 ends, and in the course of a few hours I found, that all the 

 hairs had contracted around the foreign body. 



We have here proof then, 1st, That the leaves do not Conrhi-ions 

 contract when deprived of this viscid fluid ; which ought to frorn tlieilB - 

 have been the case, if Broussonnet's theory had been accu- 

 rate. c idly, That the contraction takes place even when the 

 fluid does not cover the little glands. 3dly, That the con- 



* Sennebier, Physiol. Veg. Tome V, p, 117. 



traction 



