Chap. II.] THE EFFECTS OF REPEATED TOUCHES. 31 



them to the centre, causing, after a time, all the circum- 

 ferential tentacles to embrace it. Nevertheless, the move- 

 ments of the plant are not perfectly adapted to its require- 

 ments; for if a bit of dry moss, peat, or other rubbish, is 

 blown on to the disc, as often happens, the tentacles clasp it 

 in a useless manner. They soon, however, discover their mis- 

 take and release such innutritions objects. 



It is also a remarkable fact, that drops of water falling 

 from a height, whether under the form of natural or artificial 

 rain, do not cause the tentacles to move; yet the drops must 

 strike the glands with considerable force, more especially 

 after the secretion has been all washed away by heavy rain; 

 and this often occurs, though the secretion is so viscid that it 

 can be removed with difficulty merely by waving the leaves 

 in water. If the falling drops of water are small, they ad- 

 here to the secretion, the weight of which must be increased 

 in a much greater degree, as before remarked, than by the 

 addition of minute particles of solid matter; yet the drops 

 never cause the tentacles to become inflected. It would ob- 

 viously have been a great evil to the plant (as in the case 

 of occasional touches) if the tentacles were excited to bend 

 by every shower of rain; but this evil has been avoided by 

 the glands either having become through habit insensible to 

 the blows and prolonged pressure of drops Qf water, or to their 

 having been originally rendered sensitive solely to the contact 

 of solid bodies,* We shall hereafter see that the filaments on 

 the leaves of Dionroa are likewise insensible to the impact of 

 fluids, though exquisitely sensitive to momentary touches 

 from any solid body. 



When the pedicel of a tentacle is cut off by a sharp pair 

 of scissors quite close beneath the gland, the tentacle gener- 

 ally becomes inflected, I tried this experiment repeatedly, 

 as I was much surprised at the fact, for all other parts of the 

 pedicels are insensible to any stimuliis. These headless ten- 

 tacles after a time re-expand; but I shall return to this 

 subject. On the other hand, I occasionally succeeded in 

 crushing a gland between a pair of pincers, but this caused 

 no inflection. In this latter case the tentacles seem par- 

 alysed, as likewise follows from the action of too strong soln- 



[Pfoffer'H experiments, given nre of rnin to cause movement. 

 al)ove <p. 22), explain the fail- F. D.] 



