room mycelium called spawn. In the early days of mushroom 

 growing "the spawn was made from mycelium found growing natu- 

 rally in the fields or in the caked horse manure of the mill tracks. 

 The spawn maker planted this mycelium in special beds which were 

 later broken up and sold to the growers. This type of spawn was 

 called French-flake spawn. The original wild mycelium used to 

 inoculate these beds was called virgin spawn or mill-track spawn. 

 Spawn made according to this method was loose and easily injured 

 by excessive heat and drying out. An improvement devised in 

 England early in the nineteenth century consisted of allowing the 

 mycelium from the bits of virgin or mill-track spawn to grow into 

 compressed bricks made of a mixture of horse manure, cow manure, 

 and partly rotted leaves. This product, known as English brick 

 spawn, was superior to French-flake spawn in keeping and shipping 

 qualities. But with both types of spawn it was difficult to maintain 

 pure varieties, and often fungus diseases and insect pests were 

 distributed with the spawn. 



Spawn was first made from pure cultures in France shortly before 

 1900 and in the United States a few years later. In France spawn 

 was grown from germinated spores while in the United States the 

 mycelium was obtained by the simpler tissue-culture method, which 

 consisted of sowing in bottles of sterile manure bits of mushroom 

 tissue extracted under aseptic conditions from the caps of young 

 mushrooms. After the original spawn was obtained in pure culture 

 by these methods it was used in the place of the virgin spawn to 

 inoculate the bricks. These methods enabled the spawn maker to sell 

 spawn of known varieties and to start cultures comparatively free 

 from disease. But the spawn sold to the grower was not a pure 

 culture and there was still an opportunity for diseases and insect 

 pests to accumulate during the incubation of the bricks and to be 

 distributed with the bricks. 



About 14 years ago the most successful spawn makers in the United 

 States abandoned the tissue-culture method for the spore-culture 

 method and a few years later began selling, direct to mushroom 

 growers, quart bottles of pure-culture spawn of the type formerly 

 used to inoculate bricks. Spawn of this kind has the obvious advan- 

 tage over the old brick spawn of being free from harmful fungi and 

 insects. At the present time nearly all the spawn used in the United 

 States is bottle spawn grown from germinated spores. (Fig. 4.) 

 It gives the grower a practical approximation of pure-culture spawn, 

 pedigreed and free from diseases and insect pests, the only disad- 

 vantage being the comparatively poor keeping quality. 



PURE-CULTURE BOTTLE SPAWN 



The methods used in manufacturing bottle spawn are adaptations 

 of ordinary pure-culture laboratory technic to large-scale produc- 

 tion. The principal operations are the collection of spores, the ger- 

 mination of spores, and the preparation, transferring, and incubation 

 of spawn bottles. 



In order to obtain pure cultures, mushroom spores are collected 

 and grown under aseptic conditions. Methods of obtaining a pure 

 collection of spores are based on the fact that the young gills of 

 disease-free mushrooms develop under approximately aseptic con- 



