Dog's mercury is one of the oddest English flowers I know. Each blossom has three small green petals, and either several stamens, or else a pistil, in the centre. There is nothing particularly remarkable in the flower being green, for thousands of other flowers are green and we never notice them as in any way unusual. In fact, we never as a rule notice green blossoms at all. Yet anybody who picked a piece of dog's mercury could not fail to be struck by its curious appearance. It does not in the least resemble the inconspicuous green flowers of the stinging-nettle, or of most forest trees: it has a very distinct set of petals which at once impress one with the idea that they ought to be coloured. And so indeed they ought: for dog's mercury is a degenerate plant which once possessed a brilliant corolla and was fertilised by insects, but which has now fallen from its high estate and reverted to the less advanced mode of fertilisation by the intermediation of the wind. For some unknown reason or other this species and all its relations have discovered that they get on better by the latter and usually more wasteful plan than by the former and usually more economical one. Hence they have given up producing large bright petals, because they no longer need to attract the eyes of insects; and they have also given up the manufacture of honey, which under their new circumstances would be a mere waste of substance to them. But the dog's mercury still retains a distinct mark of its earlier insect-attracting habits in these three diminutive petals. Others of its relations have lost even these, so that the original floral form is almost completely obscured in their case. The spurges are familiar English roadside examples, and their flowers are so completely degraded that even botanists for a long time mistook their nature and analogies.