The Evolutionist at Large by Grant Allen — Read

The hedge and bank in Haye Lane are now a perfect tangled mass of creeping plants, among which I have just picked out a queer little three-cornered flower, hardly known even to village children, but christened by our old herbalists 'dog's mercury. ' It is an ancient trick of language to call coarser or larger plants by the specific title of some smaller or cultivated kind, with the addition of an animal's name. Thus we have radish and horse-radish, chestnut and horse-chestnut, rose and dog-rose, parsnip and cow-parsnip, thistle and sow-thistle. On the same principle, a somewhat similar plant being known as mercury, this perennial weed becomes dog's mercury. Both, of course, go back to some imaginary medicinal virtue in the herb which made it resemble the metal in the eyes of old-fashioned practitioners.

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.