Chap. V. EFFECTS OF ORGANIC FLUIDS. 77 



is kept in a room, and some of the central and sub- 

 marginal tentacles are thus drawn together, giving to 

 them the false appearance of having become inflected. 

 This sometimes occurs with water, as it is rendered 

 adhesive by mingling with the viscid secretion. 

 Hence the only safe criterion, and to this alone I 

 have trusted, is the bending inwards of the exterior 

 tentacles, w hich have not been touched by the fluid, or 

 at most only at their bases. In this case the move- 

 ment is wholly due to the central glands having been 

 stimulated by the fluid, and transmitting a motor 

 impulse to the exterior tentacles. The blade of the 

 leaf likewise often curves inwards, in the same manner 

 as when an insect or bit of meat is placed on the 

 disc. This latter movement is never caused, as far 

 as I have seen, by the mere drying up of an ad- 

 hesive fluid and the consequent drawing together of 

 the tentacles. 



First for the non-nitrogenous fluids. As a pre- 

 liminary trial, drops of distilled water were placed on 

 between thirty and forty leaves, and no effect whatever 

 was produced; nevertheless, in some other and rare 

 cases, a few tentacles became for a short time in- 

 flected; but this may have been caused by the 

 glands having been accidentally touched in getting 

 the leaves into a proper position. That water should 

 produce no effect might have been anticipated, as 

 otherwise the leaves would have been excited into 

 movement by every shower of rain. 



Gum arahic— Solutions of four degrees of strength were made ; 

 . one of six grains to the ounce of water (one part to 73) ; a second 

 rather stronger, yet very thin ; a third moderately thick, and a 

 fourth so thick that it would only just drop from a pointed 

 instrument. These were tried on fourteen leaves; the drops 

 being left on the discs from 24 hrs. to M hrs. ; generally about 



