Chap. XIII.] SENSITIVENESS OP FILAMENTS. 237 



sensitive. No doubt, as in the case of Drosera, the plant is 

 indiflFerent to the heaviest shower of rain. Drops of a solu- 

 tion of half an ounce of sugar to a fluid ounce of water were 

 repeatedly allowed to fall from a height on the filaments, but 

 produced no effect, unless they adhered to them. Again, I 

 blew many times through a fine pointed tube with my utmost 

 force against the filaments without any effect; such blowing 

 being received 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 solu- 

 tion 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 tem- 

 peratures varying between 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 being gently withdrawn from the water, closed rather quick- 

 ly. The three other leaves were proved to be in good condi- 

 tion, as they closed when their filaments were touched. 

 Nevertheless two fresh leaves on being dipped into water at 

 75 and 62i (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 fila- 

 ments one of them closed. This latter leaf after an addi- 

 tional 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 movements 

 in the above cases was evidently not caused by the tempera- 

 ture of the water. It has been shown that long immersion 

 causes the purple fluid within the cells of the sensitive fila- 

 ments 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 prob- 

 ably due to a slight degree of exosmose. 



I am confirmed in this belief by the effects of immersing 

 a leaf of Dionsea in a moderately strong solution of sugar; 



