The several substances mentioned in this chapter affect the colour of the glands very differently. These often become dark at first, and then very pale or white, as was conspicuously the case with glands subjected to the poison of the cobra and citrate of strychnine. In other cases they are from the first rendered white, as with leaves placed in hot water and several acids; and this, I presume, is the result of the coagulation of the albumen. On the same leaf some glands become white and others dark-coloured, as occurred with leaves in a solution of the sulphate of quinine, and in the vapour of alcohol. Prolonged immersion in nicotine, curare, and even water, blackens the glands; and this, I believe, is due to the aggregation of the protoplasm within their cells. Yet curare caused very little aggregation in the cells of the tentacles, whereas nicotine and sulphate of quinine induced strongly marked aggregation down their bases. The aggregated masses in leaves which had been immersed for 3 hrs. 15 m. 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]