256 STUDIES OF AMERICAN FUNGI. 



or vegetative part of the mushroom. Sometimes the word " fiber ' 

 is used by the mushroom growers in referring to the mycelium 

 which appears in the spawn, or in the mushroom bed. The 

 mycelium is that portion of the plant which, in the case of the wild 

 varieties, grows in the soil, or in the leaf mold, in the tree trunk or 

 other material from which the mushroom derives its food. The 

 threads of mycelium, as we know, first originated from the spore 

 of the mushroom. The spore germinates and produces delicate 

 threads, which branch and increase by growth in extent, and form 

 the mycelium. So the term spawn is rarely applied to the pure 

 mycelium, but is applied to the substratum or material in which 

 spawn is growing ; that is, the substratum and mycelium together 

 constitute the spawn. 



Natural spawn or virgin spawn. This is termed natural spawn 

 because it occurs under natural conditions of environment. The 

 original natural spawn was to be found in the fields. In the early 

 history of mushroom culture the spawn from the pastures and mead- 

 ows where mushrooms grew was one of the sources of the spawn 

 used in planting. The earth containing the spawn underneath 

 clumps of mushrooms was collected and used. 



It occurs more abundantly, however, in piles of horse manure 

 which have stood for some time in barn yards, or very often in stalls 

 where the manure is allowed to accumulate, has been thoroughly 

 tramped down and then has been left in this condition for some 

 time. It occurs also in composts, hothouse beds, or wherever 

 accumulations of horse manure are likely to occur, if other conditions 

 are congenial. The origin of the natural spawn under these condi- 

 tions of environment is probably accounted for in many cases by 

 the presence of the spores which have been in the food eaten by the 

 horse, have passed through the alimentary canal and are thus dis- 

 tributed through the dung. 



The spores present in the food of the horse may be due to 

 various conditions. Horses which go out to pasture are likely to 

 take in with the food obtained in grazing the spores scattered around 

 on the grass, and in the upper part of the sod, coming from mush- 

 rooms which grew in the field. In other cases, the spores may be 

 present in the hay, having been carried by the wind from adjacent 

 fields, if not from those which have grown in the meadow. In like 

 manner they may be present in the oats which have been fed to the 

 horse. In the case of stable-fed animals, the inoculation of the 

 manure in this way may not always be certain or very free. But 

 in the case of pasture-fed horses which are stalled at night probably 



