The way in which so curious a device has grown up is not, it seems to me, very difficult to guess. Many plants are armed with small sharp hairs which act as a protection to them against the incursions of ants and other destructive insects. These hairs are often enough more or less glandular in structure, and therefore liable to contain various waste products of the plant. Suppose one of these waste products in the ancestors of the nettle to be at first slightly pungent, by accident, as it were, then it would exercise a slightly deterrent effect upon nettle-eating animals. The more stinging it grew, the more effectual would the protection be; and as in each generation the least protected plants would get eaten down, while the more protected were spared, the tendency would be for the juice to grow more and more stinging till at last it reached the present high point of development. It is noticeable, too, that in our warrens and wild places, most of the plants are thus more or less protected in one way or another from the attacks of animals. These neglected spots are overgrown with gorse, brambles, nettles, blackthorn, and mullein, as well as with the bitter spurges, and the stringy inedible bracken. So, too, while in our meadows we purposely propagate tender fodder plants, like grasses and clovers, we find on the margins of our pastures and by our roadsides only protected species; such as thistles, houndstongue, cuckoo-pint, charlock, nettles (once more), and thorn bushes. The cattle or the rabbits eat down at once all juicy and succulent plants, leaving only these nauseous or prickly kinds, together with such stringy and innutritious weeds as chervil, plantain, and burdock. Here we see the mechanism of natural selection at work under our very eyes.