394 FIRST FORMS OF VEGETATION. 
tion called the fungus-stone, or Pietra funghaia,— 
supposed to be a species of truffle, but in reality 
nothing more than the spawn or mycelium of Poly- 
porus tuberaster, traversing masses of earth which 
it collects about it in a compact form,—constantly 
employed for the propagation of that favourite 
fungus, whose stem and pileus it readily produces 
when supplied with the requisite conditions of 
moisture and temperature. The cultivation of the 
common mushroom is too well known to require 
comment. Though considered a somewhat pre- 
carious crop, it is in the power of almost every- 
body to grow it, and when carefully conducted 
it yields a profitable return. This well-known 
species has almost entirely superseded the wild 
variety which is now very rarely to be met with in 
our woods; as is the case with all the animals 
and plants which man takes under his pro- 
tection. Mushroom spawn is sold by nurserymen 
in cakes, and for use is broken into pieces of about 
two ounces weight. When placed either ina cellar, 
out-house, or shed, where the covering is effective, 
in a bed of soil well worked into a compost by the 
droppings of horses and the parings of their hoofs, 
and allowed to heat to the temperature of new 
milk, it is certain to produce a plentiful crop. 
Microscopic fungi, such as moulds and mildews, 
may be easily cultivated in our houses by simply 
