Insectivorous Plants

Page 82

148 DROSERA ROTUNDIFOLIA. CHAP. VII: i1nmersed for a few hours in a solution, and a gland absorbs the T-:r--r'4-u-u of a grain ('00048 mg.), its colour becomes darker, though not actually black; and the contents of the cells beneath the gland are plainly aggregated. Lastly, under the same circumstances, the absorption by a gland of the QlT1f 1so-u of a grain ("00024 mg.) suffices to excite the tentacle bearing this gland into movement. NITRATE OF AMMONIA. With the salt I attended only to the inflection of the leaves, for it is far less efficient than the carbonate in causing aggrega­tion, although considerably more potent in causing inflection. I experimented with half-minims ("0296 ml .) on the discs of fifty­two 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 2 {.0 of a grain (or ·27 mg.). A solution of one part to 218 of wate1· acted most energetically, causing not only the tentacles of all the leaves, but the blades of some, to he 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 ""f"i20 of a grain ("0337 mg.). Of these leaves, seven were very strongly acted on, the edges being generally inflected; two were moderately acted on; and five not at all. I sub.sequently 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! oz.) were placed on the discs of nine leaves, so that each received the 2 loo 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 CHAP. VII. NrrRATE OF AMMONIA. 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 2 -lso of a grain (·0225 mg.), instead of, as in the last experiment, 2 ioo 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., hut 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 (21J 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 28~ 00 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. 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.