the former were greatly and the latter much more inflected. In the course of 48 hrs.

* Mucus from the air-passages is said in Marshall, 'Outlines of Physiology,' vol. ii. 1867, p. 364, to contain some albumen.

Mller's 'Elements of Physiology,' Eng. Trans. vol. i., p. 514. [page 81]

from the time when the drops were placed on the leaves, all four had almost re-expanded. They were then given little bits of meat, and these acted more powerfully than the solution. One part of isinglass was next dissolved in 437 of water; the fluid thus formed was so thin that it could not be distinguished from pure water. The usual-sized drops were placed on seven leaves, each of which thus received 1/960 of a grain (.0295 mg.). Three of them were observed for 41 hrs., but were in no way affected; the fourth and fifth had two or three of their exterior tentacles inflected after 18 hrs.; the sixth had a few more; and the seventh had in addition the edge of the leaf just perceptibly curved inwards. The tentacles of the four latter leaves began to re-expand after an additional interval of only 8 hrs. Hence the 1/960 of a grain of isinglass is sufficient to affect very slightly the more sensitive or active leaves. On one of the leaves, which had not been acted on by the weak solution, and on another, which had only two of its tentacles inflected, drops of the solution as thick as milk were placed; and next morning, after an interval of 16 hrs., both were found with all their tentacles strongly inflected.]

Altogether I experimented on sixty-four leaves with the above nitrogenous fluids, the five leaves tried only with the extremely weak solution of isinglass not being included, nor the numerous trials subsequently made, of which no exact account was kept. Of these sixty-four leaves, sixty-three had their tentacles and often their blades well inflected. The one which failed was probably too old and torpid. But to obtain so large a proportion of successful cases, care must be taken to select young and active leaves. Leaves in this condition were chosen with equal care for the sixty-one trials with non-nitrogenous fluids (water not included); and we have seen that not one of these was in the least affected. We may therefore safely conclude that in the sixty-four experiments with nitrogenous fluids the inflection of the exterior tentacles was due to the absorption of [page 82] nitrogenous matter by the glands of the tentacles on the disc.

Some of the leaves which were not affected by the non-nitrogenous fluids were, as above stated, immediately afterwards tested with bits of meat, and were thus proved to be in an active condition. But in addition to these trials, twenty-three of the leaves, with drops of gum, syrup, or starch, still lying on their discs, which had produced no effect in the course of between 24 hrs. and 48 hrs., were then tested with drops of milk, urine, or albumen. Of the twenty-three leaves thus treated, seventeen had their tentacles, and in some cases their blades, well inflected; but their powers were somewhat impaired, for the rate of movement was decidedly slower than when fresh leaves were treated with these same nitrogenous fluids. This impairment, as well as the insensibility of six of the leaves, may be attributed to injury from exosmose, caused by the density of the fluids placed on their discs.

[The results of a few other experiments with nitrogenous fluids may be here conveniently given. Decoctions of some vegetables, known to be rich in nitrogen, were made, and these acted like animal fluids. Thus, a few green peas were boiled for some time in distilled water, and the moderately thick decoction thus made was allowed to settle. Drops of the superincumbent fluid were placed on four leaves, and when these were looked at after 16 hrs., the tentacles and blades of all were found strongly inflected. I infer from a remark by Gerhardt* that legumin is present in peas "in combination with an alkali, forming an incoagulable solution," and this would mingle with boiling water.

Charles Darwin

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