260 DION^A MUSCIPULA. [Chap. XI i I. 



their having been strongly aflFected through exosmose, so that 

 they continue for some time to transmit a motor impulse to 

 the upper surface of the leaf. 



The following facts make me believe that the several 

 layers of cells forming the lower surface of the leaf are 

 always in a state of tension; and that it is owing to this 

 mechanical state, aided probably by fresh fluid being at- 

 tracted into the cells, that the lobes begin to separate or 

 expand as soon as the contraction of the upper surface di- 

 minishes. A leaf was cut oflF and suddenly plunged perpen- 

 dicularly into boiling water: I expected that the lobes would 

 have closed, but instead of doing so, they diverged a little. I 

 then took another fine leaf, with the lobes standing at an 

 angle of nearly 80 to each other; and on immersing it as 

 before, the angle suddenly increased to 90. A third leaf 

 was torpid from having recently re-expanded after having 

 caught a fly, so that repeated touches of the filaments caused 

 not the least movement; nevertheless when similarly im- 

 mersed, the lobes separated a little. As these leaves were in- 

 serted perpendicularly into the boiling water, both surfaces 

 and the filaments must have been equally affected; and I can 

 understand the divergence of the lobes only by supposing 

 that the cells on the lower side, owing to their state of ten- 

 sion, acted mechanically and thus suddenly drew the lobes a 

 little apart, as soon as the cells on the upper surface were 

 killed and lost their contractile power. We have seen that 

 boiling water in like manner causes the tentacles of Drosera 

 to curve backwards; and this is an analogous movement to 

 the divergence of the lobes of Dionsea. 



In some concluding remarks in the fifteenth chapter on 

 the Droseraceffi, the different kinds of irritability possessed 

 by the several genera, and the different manner in which 

 they capture insects, will be compared. 



