Sixty-three leaves were immersed in solutions of various strengths; other leaves being immersed at the same time in the same pure water used in making the solutions.  The results are so remarkable, though less so than with phosphate of ammonia, that I must describe the experiments in detail, but I will give only a few.  In speaking of the successive periods when inflection occurred, I always reckon from the time of first immersion. [page 150]

Having made some preliminary trials as a guide, five leaves were placed in the same little vessel in thirty minims of a solution of one part of the nitrate to 7875 of water (1 gr. to 18 oz.); and this amount of fluid just sufficed to cover them.  After 2 hrs. 10 m. three of the leaves were considerably inflected, and the other two moderately.  The glands of all became of so dark a red as almost to deserve to be called black.  After 8 hrs. four of the leaves had all their tentacles more or less inflected; whilst the fifth, which I then perceived to be an old leaf, had only thirty tentacles inflected.  Next morning, after 23 hrs. 40 m., all the leaves were in the same state, excepting that the old leaf had a few more tentacles inflected.  Five leaves which had been placed at the same time in water were observed at the same intervals of time; after 2 hrs. 10 m. two of them had four, one had seven, one had ten, of the long-headed marginal tentacles, and the fifth had four round-headed tentacles, inflected.  After 8 hrs. there was no change in these leaves, and after 24 hrs. all the marginal tentacles had re-expanded; but in one leaf, a dozen, and in a second leaf, half a dozen, submarginal tentacles had become inflected.  As the glands of the five leaves in the solution were simultaneously darkened, no doubt they had all absorbed a nearly equal amount of the salt:  and as 1/288 of a grain was given to the five leaves together, each got 1/1440 of a grain (.045 mg.).  I did not count the tentacles on these leaves, which were moderately fine ones, but as the average number on thirty-one leaves was 192, it would be safe to assume that each bore on an average at least 160.  If so, each of the darkened glands could have received only 1/230400 of a grain of the nitrate; and this caused the inflection of a great majority of the tentacles.

This plan of immersing several leaves in the same vessel is a bad one, as it is impossible to feel sure that the more vigorous leaves do not rob the weaker ones of their share of the salt.  The glands, moreover, must often touch one another or the sides of the vessel, and movement may have been thus excited; but the corresponding leaves in water, which were little inflected, though rather more so than commonly occurs, were exposed in an almost equal degree to these same sources of error.  I will, therefore, give only one other experiment made in this manner, though many were tried and all confirmed the foregoing and following results.  Four leaves were placed in