6 CIRCULAR 2 51, U. S. DEPARTMENT OP AGRICULTURE 



culture is pure it will be at least four days to two weeks before any 

 growth appears even at a favorable temperature, 75° F. When agar 

 is used the mycelium is usually allowed to make a good growth on 

 the agar before it is transferred to spawn bottles. 



The material most generally used for filling spawn bottles is 

 manure, short in straw and composted longer than for use in beds, 

 screened and partly dried. This material is tamped firmly into 

 imperial-quart milk bottles and a hole is bored through the center 

 for ventilation. The bottles are then plugged with cotton and 

 steam sterilized. At a temperature of 70° to 80° F. the mycelium 

 usually runs through the sterile manure in about 30 days. The 

 spawn from these bottles is used to inoculate compost in other 

 bottles similarly prepared. As a rule, repeated transferring is 

 limited to three generations from the original cultures to avoid so- 

 called running out and the danger of accumulating contamination. 





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Figure 5. — Autoclaves used for sterilizing spawn bottles 



Bottles newly " run " with mycelium are suitable for immediate use 

 in planting beds. If not used immediately they are usually kept in 

 cold storage. 



The following special equipment is necessary for successful spawn 

 making: A microscope to discover the nature of contaminating 

 molds; a small autoclave for the preliminary culture work; one or 

 more large canners' retorts (fig. 5) for sterilization; and apparatus 

 for measuring the reaction of media and manure. In addition, most 

 spawn makers use laundry centrifuges to dry their manure and spe- 

 cial motor-driven cutters to shred it. (Fig. 6.) This apparatus 

 and machinery must be housed, special inoculating and incubating 

 rooms are necessary, and cold-storage facilities must be provided 

 for storing spawn. The establishments of the leading spawn makers 

 represent a total capital investment of ,from $20,000 to $50,000. 

 Because of this only a few growers in the United States have 

 specialized in making spawn. These few, however, make a high 



