Page:Insectivorous Plants, Darwin, 1899.djvu/167

 Chap. VIII.] SALTS OP POTASSIUM. 147

remained quite unaffected; two seemed injured, and the sixth seemed almost dead, with its tentacles inflected. Nevertheless, after two additional days, all six leaves recovered. The immersion of three leaves for 24 hi-s., each in thirty minims of a solution of one part to 875 of water, produced no apparent effect. They were then treated with the same solution of carbonate of ammonia, with the same result as in the case of the nitrate of potash.

Potassium, Phosphate of. - Half-minims of a solution of one part to 437 of water were placed on the discs of six leaves, which were observed during three days; but no effect was produced. The partial drying up of the fluid on the disc slightly drew together the tentacles on it, as often occurs in experiments of this kind. The leaves on the third day appeared quite healthy.

Potassium, Citrate of. - Half-minims of a solution of one part to 437 of water, left on the discs of six leaves for three days, and the immersion of three leaves for 9 hrs., each in 30 minims of a solution of one part to 875 of water, did not produce the least effect.

Potassium, Oxalate of. - Half-minims were placed on different occasions on the discs of seventeen leaves; and the results perplexed me much, as they still do. Inflection supervened very slowly. After 24 hrs. four leaves out of the seventeen were well inflected, together with the blades of two; six were slightly affected, and seven not at all. Three leaves of one lot were observed for five days, and all died; but in another lot of six all excepting one looked healthy after four days. Three leaves were immersed during 9 hrs., each in 30 minims of a solution of one part to 875 of water, and were not in the least affected; but they ought to have been observed for a longer time.

Potassium, Chloride of. - Neither half-minims of a solution of one part to 437 of water, left on the discs of six leaves for three days, nor the immersion of three leaves during 25 hrs., in 30 minims of a solution of one part to 875 of water, produced the least effect. The immersed leaves were then treated with carbonate of ammonia, as described under nitrate of potash, and with the same result.

Potassium, Iodide of. - Half-minims of a solution of one part to 437 of water were placed on the discs of seven leaves. In 30 m. one leaf had the blade inflected ; after some hours three leaves had most of their submarginal tentacles mo<lerately inflected; the remaining three being very slightly affected. Hardly any of these leaves had their outer tentacles inflected. After 21 hrs. all reexpanded, excepting two which still had a few submarginal ten- tacles inflected. Three leaves were next immersed for 8 hrs. 40 m., each in 30 minims of a solution of one part to 875 of water, and were not in the least affected. I do not know what to conclude from this conflicting evidence; but it is clear that the iodide of potassium does not generally produce any marked effect.

Potassium, Bromide of. - Half-minims of a solution of one part to 437 of water were placed on the discs of six leaves; after 22 hrs. one had its blade and many tentacles inflected ; but I suspect that