Any one of the above, he admits, are as much entitled to classification as "distinct species" as the Arvensis.
The application of the title "horse-mushroom" to this last-mentioned species was generally supposed to be referable to the same popular traditions of which we see the analogies in the names horse-weed, horse-nettle, horse-balm, horseradish among the herbs--the prefix "horse" referring to the element of coarseness or rank growth. But in the instance of the mushroom it bears a deeper significance, as this ample cosmopolitan variety of the Campestris, which follows the horse all over the world, from stable and through lane to pasture, and which can only be grown in the manure of this animal, is now generally believed to be a secondary, exaggerated form consequent upon the following conditions:
The spores of the Campestris are shed in myriads in the pastures. The grazing horse no doubt swallows thousands of them, which, upon their return to the soil under especially favorable conditions for growth, vegetate into mycelium, and at length fructify in the full-formed mushroom. The dense white spawn of this species may often be seen beneath the manure in pastures where no sign of the mushroom itself is yet apparent.
During the writing of the present pages I have received from Arizona a letter accompanied with a sketch of a most astonishing mushroom, which my correspondent finds plentifully prevalent in his vicinity, growing in arid sand, even in an exceptionally dry season. He claims that "it is deliciously edible," and he has partaken of it several times. His sketch and description call to mind no existing form of mushroom known to me, though from one peculiarity in particular--namely, its frequently enormous size, "occasionally ten inches in diameter"--one would naturally expect to find it at least notorious, if not famous.
It is plainly an Agaric related to the Campestris, and from the fact of its having "pink gills darker in older specimens" I suspect it to be simply another local masquerade of this same Campestris, which suspicion, by the receipt of further data, I hope soon to verify.
This other and larger variety, so readily confounded with the Campestris, demands further and more detailed description. It may frequently be found growing in company with the former, and so closely do the two kinds merge in specimens of equal size that it is often a puzzle to separate the species. Indeed, as already mentioned by some mycologists, the larger form is considered merely as a variety of the Campestris. The accompanying plate (5) may well serve as a portrait of this species also. It frequents the same localities as the former, and is occasionally seen crowded in clusters of crescent shape, or in scattered rings, while its size is generally conspicuous, the solid cream-colored or white cap often expanding to the diameter of seven inches. Its substance discolors to yellowish brown on being bruised. The stem is less solid than in Campestris, often with a pithlike or even hollow heart. The gills are of unequal length, as in the former species, though of much the same tints of pink and brown and black, though more dingy in the lighter shades. The veil is often more conspicuous, and occasionally appears to be double, the outer or lower more or less ragged or split into a fringe at the edge. The species can hardly be mistaken for any poisonous variety, and, once recognized, its generous size, frequent profusion, and savory qualities make it a tempting quest to the epicure, being considered by many as superior in flavor to its rival, the smaller Campestris.