The phosphate of ammonia is much more powerful than the nitrate. A drop containing 1/3840 of a grain (.0169 mg.) placed on the disc of a sensitive leaf causes most of the exterior tentacles to be inflected, as well as the blade of the leaf. A minute drop containing 1/153600 of a grain (.000423 mg.), applied for a few seconds to a gland, acts, as shown by the movement of the tentacle. When a leaf is immersed in thirty minims (1.7748 ml.) of a solution of one part by weight of the salt to 21,875,000 of water, the absorption by a gland of only the 1/19760000 of a grain (.00000328 mg.), that is, about the one-twenty-millionth of a grain, is sufficient to cause the tentacle bearing this gland to bend to the centre of the leaf. In this experiment, owing to the presence of the water of crystallisation, less than the one-thirty-millionth of a grain of the efficient elements could have been absorbed. There is nothing remarkable in such minute quantities being absorbed by the glands, [page 272] for all physiologists admit that the salts of ammonia, which must be brought in still smaller quantity by a single shower of rain to the roots, are absorbed by them. Nor is it surprising that Drosera should be enabled to profit by the absorption of these salts, for yeast and other low fungoid forms flourish in solutions of ammonia, if the other necessary elements are present. But it is an astonishing fact, on which I will not here again enlarge, that so inconceivably minute a quantity as the one-twenty-millionth of a grain of phosphate of ammonia should induce some change in a gland of Drosera, sufficient to cause a motor impulse to be sent down the whole length of the tentacle; this impulse exciting movement often through an angle of above 180o. I know not whether to be most astonished at this fact, or that the pressure of a minute bit of hair, supported by the dense secretion, should quickly cause conspicuous movement. Moreover, this extreme sensitiveness, exceeding that of the most delicate part of the human body, as well as the power of transmitting various impulses from one part of the leaf to another, have been acquired without the intervention of any nervous system.