Chap. VII.] NITRATE OF AMMONIA. 121 



perimented with half-minims (.0296 c.c.) on the discs of fifty- two 

 leaves, but will give only a few cases. A solution of one part to 

 109 of water was too strong, causing little inflection, and after 24 

 hrs. killing, or nearly killing, four out of six leaves which were 

 thus tried; each of which received the yio of a grain (or .27 mg.). 

 A solution of one part to 218 of water acted most energetically, 

 causing not only the tentacles of all the leaves, but the blades of 

 some to be strongly inflected. Fourteen leaves were tried with 

 drops of a solution of one part to 875 of water, so that the disc 

 of each received the tjVo of a grain (.0337 mg.). Of these leaves, 

 seven were very strongly acted on, the edges being generally in- 

 flected; two were moderately acted on; and five not at all. I 

 subsequently tried three of these latter five leaves with urine, 

 saliva, and mucus, but they were only slightly affected; and this 

 proves that they were not in an active condition. I mention this 

 fact to show how necessary it is to experiment on several leaves. 

 Two of the leaves, which were well inflected, re-expanded after 

 61 hrs. 



In the following experiment I happened to select very sensitive 

 leaves. Half-minims of a solution of one part to 1094 of water (i. e. 

 1 gr. to 2 J oz.) were placed on the discs of nine leaves, so that each 

 received the j-^j of a grain (.027 mg.). Three of them had their 

 tentacles strongly inflected and their blades curled inwards; five 

 were slightly and somewhat doubtfully affected, having from three 

 to eight of their exterior tentacles inflected; one leaf was not at 

 all affected, yet was afterwards acted on by saliva. In six of these 

 cases, a trace of action was perceptible in 7 hrs., but the full effect 

 was not produced until from 24 hrs. to 30 hrs. had elapsed. Two of 

 the leaves, which were only slightly inflected, re-expanded after an 

 additional interval of 19 hrs. 



Half-minims of a rather weaker solution, viz. of one part to 

 1312 of water (1 gr. to 3 oz.) were tried on fourteen leaves; so 

 that each received jVnr of a grain (.0225 mg.), instead of, as in the 

 last experiment, jj^ of a grain. The blade of one was plainly in- 

 flected, as were six of the exterior tentacles; the blade of a second 

 was slightly, and two of the exterior tentacles well inflected, all 

 the other tentacles being curled in at right angles to the disc ; three 

 other leaves had from five to eight tentacles inflected; five others 

 only two or three, and occasionally, though very rarely, drops of 

 pure water cause this much action ; the four remaining leaves were 

 in no way affected, yet three of them, when subsequently tried 

 with urine, became greatly inflected. In most of these cases a 

 slight effect was perceptible in from 6 hrs. to 7 hrs., but the full 

 effect was not produced until from 24 hrs. to 30 hrs. had elapsed. 

 It is obvious that we have reached very nearly the minimum 

 amount, which, distributed between the glands of the disc, acts on 

 the exterior tentacles; these having themselves not received any 

 of the solution. 



In the next place, the viscid secretion round three of the ex- 

 terior glands was touched with the same little drop (j^j of a 

 minim) of a solution of one part to 437 of water; and after an in* 



