should therefore be made for a gradual renewal of the air in the
mushroom house. However, draughts must be avoided as tending to a too
rapid evaporation and cooling of the beds, an unfortunate condition
which cannot thereafter be entirely remedied.

=THE BEDS.=--The most common type of beds is known as the "flat bed." It
is made on the floor or on shelves as shown in the illustrations. It is
usually about 10 inches deep. Another type, principally used in France,
is known as the "ridge bed," and requires more labor than the flat bed.
The mushroom house and shelves, if used, should be frequently
disinfected and whitewashed in order to avoid danger from insects and
bacteria. The preparation of the beds and subsequent operations will be
shown in connection with the other subjects.

=PREPARATION OF THE MANURE.=--The best manure is obtained from horses
fed with an abundance of dry and nitrogenous food. The manure of animals
fed on greens is undesirable. Growers do not all follow the same method
of fermenting or composting the manure. When first unloaded, the manure
is left in its original state for a few days. It is then piled in heaps
about three feet deep and well pressed down. In this operation the
material should be carefully forked and well mixed, and wherever found
too dry, it should be lightly sprinkled. It is allowed to remain in that
condition for about six days when it is again well forked and turned. In
the latter operation it receives an additional light sprinkling; the dry
portions are turned inside in order that the whole mass may be
homogenous and uniformly moist, and the heap is again raised to about
three feet. About six days later the operation is repeated, and in about
three days the manure should be ready for the beds. It is then of a dark
brown color mixed with white, free from objectionable odor. It is
unctuous, elastic and moist, though not wet, and should not leave any
moisture in the hand.

Of course, the above rules are subject to modification according to the
condition of the manure, its age and previous handling.

=SPAWNING.=--The manure, having been properly composted, is spread
evenly on the floor or shelves and firmly compressed in beds about ten
inches in depth. The temperature of the bed is then too high for
spawning and will usually rise still higher. It should be carefully
watched with the aid of a special or mushroom thermometer. When the
temperature of the beds has fallen to abou