As to insectivorous or otherwise carnivorous plants, we have so recently here discussed this subject—before it attained to all this new popularity—that a brief account of Mr. Darwin’s investigation may suffice.[XI-2] It is full of interest as a physiological research, and is a model of its kind, as well for the simplicity and directness of the means employed as for the clearness with which the results are brought out—results which any one may verify now that the way to them is pointed out, and which, surprising as they are, lose half their wonder in the ease and sureness with which they seem to have been reached.
Rather more than half the volume is devoted to one subject, the round-leaved sundew (Drosera rotundifolia), a rather common plant in the northern temperate zone. That flies stick fast to its leaves, being limed by the tenacious seeming dew-drops which stud its upper face and margins, had long been noticed in Europe and in this country. We have heard hunters and explorers in our Northern woods refer with satisfaction to the fate which in this way often befalls one of their plagues, the black fly of early summer. And it was known to some observant botanists in the last century, although forgotten or discredited in this, that an insect caught on the viscid glands it has happened to alight upon is soon fixed by many more—not merely in consequence of its struggles, but by the spontaneous incurvation of the stalks of surrounding and untouched glands; and even the body of the leaf had been observed to incurve or become cup-shaped so as partly to involve the captive insect.
Mr. Darwin’s peculiar investigations not only confirm all this, but add greater wonders. They relate to the sensitiveness of these tentacles, as he prefers to call them, and the mode in which it is manifested; their power of absorption; their astonishing discernment of the presence of animal or other soluble azotized matter, even in quantities so minute as to rival the spectroscope—that most exquisite instrument of modern research—in delicacy; and, finally, they establish the fact of a true digestion, in all essential respects similar to that of the stomach of animals.