Mercury,

Mercury, Dog's (Mercurialis), a genus of plants of the natural order Euphorbiaceæ. The Common Dog's Mercury (M. perennis) is very common in woods and shady places in Britain. It has a perfectly simple stem, about a foot high, with rough ovate leaves, and axillary loose spikes of greenish flowers. It turns a glaucous black colour in drying, and the root contains two colouring substances, one blue and the other carmine. It is very poisonous. The mercury which some old writers mention as a potherb is not this plant, but English Mercury, or Wild Spinach (Chenopodium bonus-Henricus). Annual Dog's Mercury (M. annua) is a much rarer British plant, and less poisonous. The leaves are indeed eaten in Germany as spinach. A half-shrubby species (M. tomentosa), found in the countries near the Mediterranean, has enjoyed an extraordinary reputation from ancient times; the absurd belief mentioned by Pliny being still retained, that if a woman after conception drink the juice of the male plant she will give birth to a boy, and if of the female plant her offspring will be a girl.