"The edible mushroom (Agaricus Campestris) is, after some little observation, easily distinguished from other species. In the pasture fields they vary in diameter from the size of a button to that of a saucer. In the young stage, which is the proper time to gather them, they are white on top and delicate pale pink beneath. As they get older the underneath side, or "gills," turn black."
January 1, 1970
https://en.wikiquote.org/wiki/Fungiculture