grass.  The glands on the discs of the above leaves, instead of being almost black, as after the first hour, were now after 23 hrs. very pale.  I next tried on four leaves half-minims of a weaker solution, of one part to 1312 of water (1 gr. to 3 oz.); so that each received 1/2880 of a grain (.0225 mg.).  After 2 hrs. 18 m. the glands on the disc were very dark-coloured; after 24 hrs. two of the leaves were slightly affected; the other two not at all.

Acetate of Ammonia.—­Half-minims of a solution of about one part to 109 of water were placed on the discs of two leaves, both of which were acted on in 5 hrs. 30 m., and after 23 hrs. had every single tentacle closely inflected.

Oxalate of Ammonia.—­Half-minims of a solution of one part to 218 of water were placed on two leaves, which, after 7 hrs., became moderately, and after 23 hrs. strongly, inflected.  Two other leaves were tried with a weaker solution of one part to 437 of water; one was strongly inflected in 7 hrs.; the other not until 30 hrs. had elapsed.

Tartrate of Ammonia.—­Half-minims of a solution of one part to 437 of water were placed on the discs of five leaves.  In 31 m. there was a trace of inflection in the exterior tentacles of some of the leaves, and this became more decided after 1 hr. with all the leaves; but the tentacles were never closely inflected.  After 8 hrs. 30 m. they began to re-expand.  Next morning, after 23 hrs., all were fully re-expanded, excepting one which was still slightly inflected.  The shortness of the period of inflection in this and the following case is remarkable.

Chloride of Ammonium.—­Half-minims of a solution of one part to 437 of water were placed on the discs of six leaves.  A decided degree of inflection in the outer and submarginal tentacles was perceptible in 25 m.; and this increased during the next three or four hours, but never became strongly marked.  After only 8 hrs. 30 m. the tentacles began to re-expand, and by the next morning, after 24 hrs., were fully re-expanded on four of the leaves, but still slightly inflected on two.]

General Summary and Concluding Remarks on the Salts of Ammonia.—­We have now seen that the nine [page 168] salts of ammonia which were tried, all cause the inflection of the tentacles, and often of the blade of the leaf.  As far as can be ascertained from the superficial trials with the last six salts, the citrate is the least powerful, and the phosphate certainly by far the most.  The tartrate and chloride are remarkable from the short duration of their action.  The relative efficiency of the carbonate, nitrate, and phosphate, is shown in the following table by the smallest amount which suffices to cause the inflection of the tentacles.

Column 1 :  Solutions, how applied.  Column 2 :  Carbonate of Ammonia.  Column 3 :  Nitrate of Ammonia.  Column 4 :  Phosphate of Ammonia.

Placed on the glands of the disc, so as to act indirectly on the outer tentacles :  1/960 of a grain, or 0675 mg. :  1/2400 of a grain, or .027 mg. :  1/3840 of a grain, or .0169 mg.