A solution of the carbonate is absorbed by the roots and induces aggregation in their cells, but does not affect the leaves.  The vapour is absorbed by the glands, and causes inflection as well as aggregation.  A drop of a solution containing 1/960 of a grain (.0675 mg.) is the least quantity which, when placed on the glands of the disc, excites the exterior tentacles to bend inwards.  But a minute drop, containing 1/14400 of a grain (.00445 mg.), if applied for a few seconds to the secretion surrounding a gland, causes the inflection of the same tentacle.  When a highly sensitive leaf is immersed in a solution, and there is ample time for absorption, the 1/268800 of a grain [page 271] (.00024 mg.) is sufficient to excite a single tentacle into movement.

The nitrate of ammonia induces aggregation of the protoplasm much less quickly than the carbonate, but is more potent in causing inflection.  A drop containing 1/2400 of a grain (.027 mg.) placed on the disc acts powerfully on all the exterior tentacles, which have not themselves received any of the solution; whereas a drop with 1/2800 of a grain caused only a few of these tentacles to bend, but affected rather more plainly the blade.  A minute drop applied as before, and containing 1/28800 of a grain (.0025 mg.), caused the tentacle bearing this gland to bend.  By the immersion of whole leaves, it was proved that the absorption by a single gland of 1/691200 of a grain (.0000937 mg.) was sufficient to set the same tentacle into movement.

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