Iron, Chloride of.—Three leaves were immersed in ninety minims of a solution of one part to 437 of water; in 8 hrs. no inflection; but after 24 hrs. considerable inflection; glands blackened; fluid coloured yellow, with floating flocculent particles of oxide of iron. The leaves were then placed in water; after 48 hrs. they had re-expanded a very little, but I think were killed; glands excessively black.
Chromic Acid.—One part to 437 of water; three leaves were immersed in ninety minims; in 30 m. some, and in 1 hr. considerable, inflection; after 2 hrs. all the tentacles closely inflected, with the glands discoloured. Placed in water, next day leaves quite discoloured and evidently killed.
Manganese, Chloride of.—Three leaves immersed in ninety minims of a solution of one part to 437 of water; after 22 hrs. no more inflection than often occurs in water; glands not blackened. The leaves were then placed in the usual solution of phosphate of ammonia, but no inflection was caused even after 48 hrs.
Copper, Chloride of.—Three leaves immersed in ninety minims [page 186] of a solution of one part to 437 of water; after 2 hrs. some inflection; after 3 hrs. 45 m. tentacles closely inflected, with the glands blackened. After 22 hrs. still closely inflected, and the leaves flaccid. Placed in pure water, next day evidently dead. A rapid poison.
Nickel, Chloride of.—Three leaves immersed in ninety minims of a solution of one part to 437 of water; in 25 m. considerable inflection, and in 3 hrs. all the tentacles closely inflected. After 22 hrs. still closely inflected; most of the glands, but not all, blackened. The leaves were then placed in water; after 24 hrs. remained inflected; were somewhat discoloured, with the glands and tentacles dingy red. Probably killed.
Cobalt, Chloride of.—Three leaves immersed in ninety minims of a solution of one part to 437 of water; after 23 hrs. there was not a trace of inflection, and the glands were not more blackened than often occurs after an equally long immersion in water.
Platinum, Chloride of.—Three leaves immersed in ninety minims of a solution of one part to 437 of water; in 6 m. some inflection, which became immense after 48 m. After 3 hrs. the glands were rather pale. After 24 hrs. all the tentacles still closely inflected; glands colourless; remained in same state for four days; leaves evidently killed.]
Concluding Remarks on the Action of the foregoing Salts.—Of the fifty-one salts and metallic acids which were tried, twenty-five caused the tentacles to be inflected, and twenty-six had no such effect, two rather doubtful cases occurring in each series. In the table at the head of this discussion, the salts are arranged according to their chemical affinities; but their action on Drosera does not seem to be thus governed. The nature of the base is far more important, as far as can be judged from the few experiments here given, than that of the acid; and this is the conclusion at which physiologists have arrived with respect to animals. We see this fact illustrated in all the nine salts of soda causing inflection, and in not being poisonous except when given in large doses; whereas seven of [page 187] the corresponding salts of potash do not cause inflection, and some of them are poisonous. Two of them, however, viz. the oxalate and iodide of potash, slowly induced a slight and rather doubtful amount of inflection. This difference between the two series is interesting, as Dr. Burdon Sanderson informs me that sodium salts may be introduced in large doses into the circulation of mammals without any injurious effects; whilst small doses of potassium salts cause death by suddenly arresting the movements of the heart. An excellent instance of the different action of the two series is presented by the phosphate of soda quickly causing vigorous inflection, whilst phosphate of potash is quite inefficient. The great power of the former is probably due to the presence of phosphorus, as in the cases of phosphate of lime and of ammonia. Hence we may infer that Drosera cannot obtain phosphorus from the phosphate of potash. This is remarkable, as I hear from Dr. Burdon Sanderson that phosphate of potash is certainly decomposed within the bodies of animals. Most of the salts of soda act very rapidly; the iodide acting slowest. The oxalate, nitrate, and citrate seem to have a special tendency to cause the blade of the leaf to be inflected. The glands of the disc, after absorbing the citrate, transmit hardly any motor impulse to the outer tentacles; and in this character the citrate of soda resembles the citrate of ammonia, or a decoction of grass-leaves; these three fluids all acting chiefly on the blade.
It seems opposed to the rule of the preponderant influence of the base that the nitrate of lithium causes moderately rapid inflection, whereas the acetate causes none; but this metal is closely allied to sodium [page 188] and potassium,* which act so differently; therefore we might expect that its action would be intermediate. We see, also, that caesium causes inflection, and rubidium does not; and these two metals are allied to sodium and potassium. Most of the earthy salts are inoperative. Two salts of calcium, four of magnesium, two of barium, and two of strontium, did not cause any inflection, and thus follow the rule of the preponderant power of the base. Of three salts of aluminium, one did not act, a second showed a trace of action, and the third acted slowly and doubtfully, so that their effects are nearly alike.
Of the salts and acids of ordinary metals, seventeen were tried, and only four, namely those of zinc, lead, manganese, and cobalt, failed to cause inflection. The salts of cadmium, tin, antimony, and iron, act slowly; and the three latter seem more or less poisonous. The salts of silver, mercury, gold, copper, nickel, and platinum, chromic and arsenious acids, cause great inflection with extreme quickness, and are deadly poisons. It is surprising, judging from animals, that lead and barium should not be poisonous. Most of the poisonous salts make the glands black, but chloride of platinum made them very pale. I shall have occasion, in the next chapter, to add a few remarks on the different effects of phosphate of ammonia on leaves previously immersed in various solutions.