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Reviews.

INSECTIVOROUS PLANTS. By CHARLES DARWIN, M.A., F.R.S. London: J. Murray. 1875.

This new work of Mr. Darwin's will be of special interest to those who took part in, or followed the discussion which occupied our columns a few months ago, on the alleged carnivorous habits of the sundew, butterwort, and some other plants. Those who denied the alleged facts, from the absence of a digestive organ in these plants, will probably now see that they came to too hasty a conclusion. From a long series of experiments on Drosera, Pinguicula, Utricularia, Dionæa, and some other less known plants, extending, in the case of the first named genus, over fifteen years, and conducted with the patience and precision and a careful elimination of all sources of error which distinguish all Mr. Darwin's researches, he has shown, beyond apparently all controversy, that there are certain plants which have not only the power of absorbing nitrogenous nutrient substances through their leaves, but of absolutely digesting these substances by the secretion of a fluid, which, like the gastric juice, becomes distinctly acid when excited by the presence of food. This substance analogous in its function to pepsine, has been analysed by Professor Frankland, though in too small quantities to obtain reliable results. His conclusion, however, is that an acid analogous to or identical with butyric is formed. The methods of capturing their prey vary in the different genera. Utricularia has bladders provided with a valve which allows the ingress but prevents the egress of small animals; Dionæa possesses sensitive hairs, irritation of which causes the sudden collapse of the leaf upon the imprisoned insect; Drosera has glandular hairs or "tentacles" which secrete a viscid juice, in the toils of which small animals are hopelessly entangled; in Pinguicula the margins of the leaf become gradually incurved. The infinitesimally small quantity of nitrogenous matter which causes inflection of the glands of Drosera is almost past belief, and would be regarded as altogether incredible were it not for the extreme care and accuracy with which Mr. Darwin is known to conduct his experiments. A dose of 1/134000 of a grain of carbonate of ammonia given to a single gland suffices to produce a well-marked effect; a minute drop containing 1/133600 of a grain of phosphate of ammonia, if held for a few seconds in contact with the gland, causes it to be inflected; and if a leaf is left immersed for a few hours in a solution so weak that each gland only absorb 1/19760000 of a grain sensible motion of the tentacles results.

It is impossible, in a short notice, even to allude to the various points of interest brought out in this volume, which may fairly be styled a chapter in the romance, or rather perhaps in the tragedy of natural history. One by one we see the artificial limes of demarcation which have been set up between the animal and vegetable worlds thrown down, and the uniformity of the laws of nature established. But even those who have had the least faith in an absolute distinction between the modes in which plants and animals obtain their food, have hardly been prepared for so close a simulation of the process of digestion to be discovered in plants. The present instance is not the first in which our great physiologist has acted as pioneer in looking up new tracks, and indicating the road to discoveries which have been most pregnant in increasing our knowledge of the phenomena of animal and vegetable life.