292 DION^A MUSCIPULA. Chap. XI 11. 



with as much indifference as no doubt is a heavy gale 

 of wind. We thus see that the sensitiveness of the 

 filaments is of a specialised nature, being related to a 

 momentary touch rather than to prolonged pressure ; 

 and the touch must not be from fluids, such as air or 

 water, but from some solid object. 



Although drops of water and of a moderately strong 

 solution of sugar, falling on the filaments, does not 

 excite them, yet the immersion of a leaf in pure water 

 sometimes caused the lobes to close. One leaf was left 

 immersed for 1 hr. 10 m., and three other leaves for 

 some minutes, in water at temperatures varying be- 

 tween 59^ and 65° (15° to 18°-3 Cent.) without any 

 effect. One, however, of these four leaves, on being 

 gently withdrawn from the water, closed rather 

 quickly. The three other leaves were proved to be in 

 good condition, as they closed when their filaments 

 were touched. Nevertheless two fresh leaves on being 

 dipped into water at 75° and 62^° (23°-8 and 16°-9 

 Cent.) instantly closed. These were then placed with 

 their footstalks in water, and after 23 hrs. partially 

 re-expanded ; on touching their filaments one of 

 them closed. This latter leaf after an additional 

 24 hrs. again re-expanded, and now, on the filaments 

 of both leaves being touched, both closed. We thus 

 see that a short immersion in water does not at all 

 injure the leaves, but sometimes excites the lobes 

 to close. The movement in the above cases was 

 evidently not caused by the temperature of the water. 

 It has been shown that long immersion causes the 

 purple fluid within the cells of the sensitive filaments 

 to become aggregated ; and the tentacles of Drosera 

 are acted on in the same manner by long immersion, 

 often being somewhat inflected. In both cases the 

 result is probably due to a slight degree of exosmose. 



