114 



DROSERA ROTUNDIFOLIA. 



[Chap. VII. 



we can judge whether a solution produces any effect only by ob- 

 serving the exterior tentacles M'itfaiin the first 3 or 4 hrs. after im- 

 mersion. 



Now for a summary of the state of the 173 leaves after an im- 

 mersion of 3 or 4 hrs. in pure water. One leaf had almost all 

 its tentacles inflected ; three leaves had most of them sub-inflected ; 

 and thirteen had on an average 3G.5 tentacles inflected. Thus seven- 

 teen leaves out of the 173 were acted on in a marked manner. 

 Eighteen leaves had from- seven to nineteen tentacles inflected, the 

 average being 9.3 tentacles for each leaf. Forty-four leaves had 

 from one to six tentacles inflected, generally the long-headed ones. 

 So that altogether of the 173 leaves carefully observed, seventy- 

 nine were affected by the water in 

 some degree, though commonly 

 to a very slight degree; and nine- 

 ty-four were not affected in the 

 least degree. This amount of in- 

 flection is utterly insignificant, as 

 we shall hereafter see, compared 

 with that caused by very weak 

 solutions of several salts of am- 

 monia. 



Plants which have lived for 

 some time in a rather high tem- 

 perature are far more sensitive to 

 the action of water than those 

 giown out of doors, or recently 

 brought into a warm greenhouse. 

 Thus in the above seventeen cases, 

 in which the immersed leaves hod 

 a considerable number of ten- 

 tacles inflected, the plants had 

 been kept during the winter in a 

 very warm greenhouse; and they 

 bore in the early spring remark- 

 obly fine leaves, of a light red col- 

 our. Had 1 then known that the 

 sensitiveness of plants was thus 

 increased, perhaps 1 should not 

 have use<l the leaves for my experiments with the very weak solu- 

 tions of phosphate of ammonia; but my experimenta are not thus 

 vitiatecl, as I invariably used leaves from the same plants for simul- 

 taneous immersion in water. It often hapiH-'ned that some leaves 

 on the same plant, and some tentacles on the same leaf, were more 

 sensitive than others; but why this should be so, I do not know. 

 Besides the differences just indicated between the leaves im- 

 mersed in water and in weak solutions of ammonia, the tentacles of 

 the latter are in most cases much more closely inflected. The ap- 

 pearance of a leaf after immersion in a few drops of a solution of 

 one grain of phosphate of ammonia to 200 oz. of water (i. e. one 

 part to 87,500) is here reproduced: such energetic inflection is never 



Fio. 9. 

 (Drogera rotundifolia.) 

 Leaf (enlarged) with all the ten- 

 tacles cl()(H-Iy infltH-tcd, frum im- 

 mersion in a solution of phos- 

 phate of ammonia (one part to 

 87,500 of water). 



