in a saturated solution of sulphate of quinine exhibited incessant [page 226] changes of form, but after 24 hrs. were motionless; the leaf being flaccid and apparently dead. On the other hand, with leaves subjected for 48 hrs. to a strong solution of the poison of the cobra, the protoplasmic masses were unusually active, whilst with the higher animals the vibratile cilia and white corpuscles of the blood seem to be quickly paralysed by this substance.
With the salts of alkalies and earths, the nature of the base, and not that of the acid, determines their physiological action on Drosera, as is likewise the case with animals; but this rule hardly applies to the salts of quinine and strychnine, for the acetate of quinine causes much more inflection than the sulphate, and both are poisonous, whereas the nitrate of quinine is not poisonous, and induces inflection at a much slower rate than the acetate. The action of the citrate of strychnine is also somewhat different from that of the sulphate.
Leaves which have been immersed for 24 hrs. in water, and for only 20 m. in diluted alcohol, or in a weak solution of sugar, are afterwards acted on very slowly, or not at all, by the phosphate of ammonia, though they are quickly acted on by the carbonate. Immersion for 20 m. in a solution of gum arabic has no such inhibitory power. The solutions of certain salts and acids affect the leaves, with respect to the subsequent action of the phosphate, exactly like water, whilst others allow the phosphate afterwards to act quickly and energetically. In this latter case, the interstices of the cell-walls may have been blocked up by the molecules of the salts first given in solution, so that water could not afterwards enter, though the molecules of the phosphate could do so, and those of the carbonate still more easily. [page 227]
The action of camphor dissolved in water is remarkable, for it not only soon induces inflection, but apparently renders the glands extremely sensitive to mechanical irritation; for if they are brushed with a soft brush, after being immersed in the solution for a short time, the tentacles begin to bend in about 2 m. It may, however, be that the brushing, though not a sufficient stimulus by itself, tends to excite movement merely by reinforcing the direct action of the camphor. The vapour of camphor, on the other hand, serves as a narcotic.
Some essential oils, both in solution and in vapour, cause rapid inflection, others have no such power; those which I tried were all poisonous.
Diluted alcohol (one part to seven of water) is not poisonous, does not induce inflection, nor increase the sensitiveness of the glands to mechanical irritation. The vapour acts as a narcotic or anaesthetic, and long exposure to it kills the leaves.
The vapours of chloroform, sulphuric and nitric ether, act in a singularly variable manner on different leaves, and on the several tentacles of the same leaf. This, I suppose, is owing to differences in the age or constitution of the leaves, and to whether certain tentacles have lately been in action. That these vapours are absorbed by the glands is shown by their changed colour; but as other plants not furnished with glands are affected by these vapours, it is probable that they are likewise absorbed by the stomata of Drosera. They sometimes excite extraordinarily rapid inflection, but this is not an invariable result. If allowed to act for even a moderately long time, they kill the leaves; whilst a small dose acting for only a short time serves as a narcotic or anaesthetic. In this case the tentacles, whether or not they have [page 228] become inflected, are not excited to further movement by bits of meat placed on the glands, until some considerable time has elapsed. It is generally believed that with animals and plants these vapours act by arresting oxidation.
Exposure to carbonic acid for 2 hrs., and in one case for only 45 m., likewise rendered the glands insensible for a time to the powerful stimulus of raw meat. The leaves, however, recovered their full powers, and did not seem in the least injured, on being left in the air for 24 or 48 hrs.