this aggregation is not dependent upon absorption, for it equally occurs from mechanical irritation of the gland, and always accompanies inflection, however caused, though it may take place without it.  This is also apparent from the astonishingly minute quantity of certain substances which suffices to produce sensible inflection and aggregation—­such, for instance, as the 1/20000000 or even the 1/30000000 of a grain of phosphate or nitrate of ammonia!

By varied experiments it was found that the nitrate of ammonia was more powerful than the carbonate, and the phosphate more powerful than the nitrate, this result being intelligible from the difference in the amount of nitrogen in the first two salts, and from the presence of phosphorus in the third.  There is nothing surprising in the absorption of such extremely dilute solutions by a gland.  As our author remarks:  “All physiologists admit that the roots of plants absorb the salts of ammonia brought to them by the rain; and fourteen gallons of rain-water contain a grain of ammonia; therefore, only a little more than twice as much as in the weakest solution employed by me.  The fact which appears truly wonderful is that the 1/20000000 of a grain of the phosphate of ammonia, including less than 1/30000000 of efficient matter (if the water of crystallization is deducted), when absorbed by a gland, should induce some change in it which leads to a motor impulse being transmitted down the whole length of the tentacle, causing its basal part to bend, often through an angle of 180 degrees.”  But odoriferous particles which act upon the nerves of animals must be infinitely smaller, and by these a dog a quarter of a mile to the leeward of a deer perceives his presence by some change in the olfactory nerves transmitted through them to the brain.

When Mr. Darwin obtained these results, fourteen years ago, he could claim for Drosera a power and delicacy in the detection of minute quantities of a substance far beyond the resources of the most skillful chemist; but in a foot-note he admits that “now the spectroscope has altogether beaten Drosera; for, according to Bunsen and Kirchhoff, probably less than the 1/200000000 of a grain of sodium can be thus detected.”

Finally, that this highly-sensitive and active living organism absorbs, will not be doubted when it is proved to digest, that is, to dissolve otherwise insoluble animal matter by the aid of special secretions.  That it does this is now past doubting.  In the first place, when the glands are excited they pour forth an increased amount of the ropy secretion.  This occurs directly when a bit of meat is laid upon the central glands; and the influence which they transmit to the long-stalked marginal glands causes them, while incurving their tentacles, to secrete more copiously long before they have themselves touched anything.  The primary fluid, secreted without excitation, does not of itself digest.  But the secretion under