This section is from "The Horticulturist, And Journal Of Rural Art And Rural Taste", by P. Barry, A. J. Downing, J. Jay Smith, Peter B. Mead, F. W. Woodward, Henry T. Williams. Also available from Amazon: Horticulturist and Journal of Rural Art and Rural Taste.
The next preparation is a quantity of good spawn, which may be made as follows: Take equal portions of unfermented horse and cow manure, and fresh earth from a pasture field; mix and work these together. Add sufficient water to reduce the mass into the consistency of stiff mortar. Mould into the form, and about the size of common building bricks; set into an open shed, and turn them over once a day, until nearly dried through; then cut a hole of an inch diameter into the centre of each; fill up with a piece of good spawn, and paste over the aperture with a little cow dung; build the whole into a conical heap, first strewing some littery stable manure underneath, and, as the work proceeds, fill in between each layer with an inch of half-fermented, dry, horse drop-Eings; cover with a few inches of the same, and as much litter as will enable the heap to acquire a gentle warmth, but not more, or the spawn will be killed. In the summer time, there is generally heat enough without any fermentation, and care should be used on this point.
If all goes on well, the rhizoma will have penetrated through the whole substance in three or four weeks, which may be known by its appearing full of fine, white threads; but if, when examined, it is found to be only so around the piece previously put in, the spawn is not sufficiently run, and it should be left undisturbed a week or two longer. After this time, examine again, and do not let it become too far advanced, or the keeping properties will be very much depreciated. When all is right, remove the bricks into a dry and cool room, protected from frost in winter, where they may be preserved good for several years. I have used Mushroom spawn five years old, and found it as good as when first made. Hitherto, we have only shown so far as to require a small portion of " leaven" to commence with, and there are many persons so situated as not to be able to get this. There are not many places, however, where horses, cows, or sheep, are not stabled, and the manure lying around, and it often happens that more or less has been accidentally protected from extreme wet These are the spots to look for natural spawn, and, when found, a very small portion is enough for a start.
Do not collect any that may be produced from decaying wood or leaves, for, notwithstanding it mar run in the prepared compost, there is danger of its not being the right kind. It may be another species of the same genus, and probably a poisonous one; while, by attending to this advice, the true sort is sure to be obtained. The edible Mushroom may always be known by its plump, solid, and fleshy appearance, brittle texture, and, above all, the beautiful pink color of the lamina, or gills, on the under side of the pileus, or cap; it has also a peculiarly delicate scent, while the poisonous species generally emit a rank and somewhat pungent odor, attended by a clammy or greasy excrescence on the outside.