acted on, the edges being generally inflected; 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 51 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 1/2 oz.) were placed on the discs of nine leaves, so that each received the 1/2400 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 [page 149] 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 1/2880 of a grain (.0225 mg.), instead of, as in the last experiment, 1/2400 of a grain.  The blade of one was plainly inflected, 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 here 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 exterior glands was touched with the same little drop (1/20 of a minim) of a solution of one part to 437 of water; and after an interval of 2 hrs. 50 m. all three tentacles were well inflected.  Each of these glands could have received only the 1/28800 of a grain, or .00225 mg.  A little drop of the same size and strength was also applied to four other glands, and in 1 hr. two became inflected, whilst the other two never moved.  We here see, as in the case of the half-minims placed on the discs, that the nitrate of ammonia is more potent in causing inflection than the carbonate; for minute drops of the latter salt of this strength produced no effect.  I tried minute drops of a still weaker solution of the nitrate, viz. one part to 875 of water, on twenty-one glands, but no effect whatever was produced, except perhaps in one instance.