I will give only one other experiment.  After the exposure of a plant for 2 hrs. to the gas, one of its leaves was immersed in a rather strong solution of carbonate of ammonia, together with [page 223] a fresh leaf from another plant.  The latter had most of its tentacles strongly inflected within 30 m.; whereas the leaf which had been exposed to the carbonic acid remained for 24 hrs. in the solution without undergoing any inflection, with the exception of two tentacles.  This leaf had been almost completely paralysed, and was not able to recover its sensibility whilst still in the solution, which from having been made with distilled water probably contained little oxygen.]

Concluding Remarks on the Effects of the foregoing Agents.—­As the glands, when excited, transmit some influence to the surrounding tentacles, causing them to bend and their glands to pour forth an increased amount of modified secretion, I was anxious to ascertain whether the leaves included any element having the nature of nerve-tissue, which, though not continuous, served as the channel of transmission.  This led me to try the several alkaloids and other substances which are known to exert a powerful influence on the nervous system of animals; I was at first encouraged in my trials by finding that strychnine, digitaline, and nicotine, which all act on the nervous system, were poisonous to Drosera, and caused a certain amount of inflection.  Hydrocyanic acid, again, which is so deadly a poison to animals, caused rapid movement of the tentacles.  But as several innocuous acids, though much diluted, such as benzoic, acetic, &c., as well as some essential oils, are extremely poisonous to Drosera, and quickly cause strong inflection, it seems probable that strychnine, nicotine, digitaline, and hydrocyanic acid, excite inflection by acting on elements in no way analogous to the nerve-cells of animals.  If elements of this latter nature had been present in the leaves, it might have been expected that morphia, hyoscyamus, atropine, veratrine, colchicine, curare, and diluted alcohol would have produced some marked effect; whereas [page 224] these substances are not poisonous and have no power, or only a very slight one, of inducing inflection.  It should, however, be observed that curare, colchicine, and veratrine are muscle-poisons—­that is, act on nerves having some special relation with the muscles, and, therefore, could not be expected to act on Drosera.  The poison of the cobra is most deadly to animals, by paralysing their nerve-centres,* yet is not in the least so to Drosera, though quickly causing strong inflection.