In 1875 appeared another great work from the master's pen, "Insectivorous Plants," which was destined to place in a yet more striking light the many-sidedness and fertility of his mind. As usual Darwin tells us that this work dated from many years back. "During the summer of 1860," he says, "I was surprised by finding how large a number of insects were caught by the leaves of the common sun-dew (_Drosera rotundifolia_) on a heath in Sussex. I had heard that insects were thus caught, but knew nothing further on the subject. I gathered by chance a dozen plants, bearing fifty-six fully expanded leaves, and on thirty-one of these dead insects or remnants of them adhered." Here was the germ of something, the discoverer scarcely knew what. It was evident to him that the little sun-dew was excellently adapted for catching insects, and that the number of them thus slaughtered annually must be enormous. What bearing might this have upon the problem of the struggle for existence? A masterly series of experiments was forthwith set on foot, with the result of proving that sun-dews and a number of other plants obtain the bulk of their nourishment by catching, killing, and digesting insects. They may be called truly carnivorous plants. What an unexpected reversal this was of the order of things hitherto believed to prevail universally. Animals live on other animals or on plants. Here were plants living on animals, and keeping down their number. Moreover, without a nervous system, the action of the parts of a sun-dew leaf was proved to be as apparently purposive as the combined action of the limbs of an animal. Without a stomach, the sun-dew poured forth a digestive fluid as effective in extracting and fitting the nutritious matter of the insect for its own purposes as that of an animal. Without sensory nerve-endings, there was a percipient power in the sun-dew which recognised instinctively and at once the non-nutritious nature of various objects, and which responded to the most delicate chemical stimuli and to the minutest weights. We cannot describe the little sun-dew better than in Darwin's own words: "It bears from two or three to five or six leaves, generally extended more or less horizontally, but sometimes standing vertically upwards. The leaves are commonly a little broader than long. The whole upper surface is covered with gland-bearing filaments, or tentacles as I shall call them from their manner of acting. The glands were counted on thirty-one leaves, but many of these were of unusually large size, and the average number was 192; the greatest number being 260, and the least 130. The glands are each surrounded by large drops of extremely viscid secretion, which, glittering in the sun, have given rise to the plant's poetical name of the sun-dew."