60 LEVINE: SPORADIC APPEARANCE OF NON-EDIBLE MUSHROOMS 
pasture, and filling them with thoroughly fermented manure. 
The vigorously growing mycelium spreads into this manure after 
several weeks. When this occurs, the manure is taken out of the 
trenches and slowly dried. This constitutes “virgin spawn,”’ 
from which the commercial spawn is made. By this method 
it is conceivable that the mycelia of a number of fungi may be 
found growing in the “virgin spawn” and be propagated in the 
commercial spawn. This at least seems to be a plausible explana- 
tion for the introduction of P. venenosus into mushroom houses. 
This is supported by the fact that the fungus appeared only 
after the beds were spawned; as mentioned above it appeared in 
two widely separated mushroom establishments, both of which, 
however, were using the spawn from the same spawn maker. How 
P. venenosus escapes observation in the field is still a question that 
remains unsolved. 
It is possible that the plant is a species of Psilocybe or Inocybe 
made aberrant by cultural conditions. Another possibility may 
be that the mycelium never has conditions in the open favorable 
to the development of sporophores but produces fruit bodies under 
cultivation only. 
Clitocybe dealbata Sow. (PLATE 2, FIGS. 15-17). A species of 
Clitocybe which I have identified as belonging to the variable 
species known as Clitocybe dealbata also appeared. These plants 
were found in several mushroom houses in great abundance, 
growing in large clumps in the beds of Agaricus campestris. The 
Clitocybe species were found in these houses from January to 
May. 
There are three recognized varieties of Chlitocybe dealbata Sow.., 
namely, var. minor Cooke, var. deformata Peck, and var. sudorifica 
Peck. The var. sudorifica was later made a species by Peck. 
The essential diagnostic characteristics of these plants, as given 
by: Peck follow. C. dealbata has a white, fleshy pileus with a 
Wavy margin; the gills are close, thin, adnate, and white in 
color; the stipe is fibrous, equal, and stuffed or hollow. Var. 
minor differs from the typical form of the species in its smaller 
and more regular form, its opaque gills, and the pleasant farin- 
aceous odor. Var. deformata has a thin white, and very irregular 
pileus with a wavy or lobed margin; the gills are adnate or 
