20 BULLETIN 127, U. S. DEPARTMENT OF AGRICULTURE. 



of the gas may prove injurious. Formaldehyde has a distressing 

 effect upon the eyes, and also attacks the mucous membranes, with 

 consequent discomfort. 



The potassium permanganate may be placed in the receptacles first, 

 which should be of selected size, so that it will just cover the base of 

 the receptacle. This was the method followed in the cultural experi- 

 ments, but, as already stated, for general practice it was found more 

 convenient to place the formaldehyde in the receptacles first. 



The formalin-permanganate method of fumigation differs radically 

 from other methods. The potassium permanganate is decomposed 

 b}" a part of the formalin, and the heat of this chemical reaction serves 

 to liberate formaldehyde gas. 



Formaldehyde gas is explosive when in a confined place, such as a 

 mushroom house; consequently, all lights must he kept away from the 

 houses while they are being fumigated. Even after the receptacles 

 containing the formalin are placed in the houses, they should not be 

 entered by persons with lights. 



The houses should be kept closed for at least 24 hours. If possible, 

 they should be unopened until just before the new beds are to be 

 installed, thus preventing any chance of their being infected meantime. 

 Under no circumstance should the houses be opened until the manure 

 which had been taken from them has been removed and the ground 

 where it was placed thoroughly disinfected in the manner described. 



CONCLUSIONS. 



The disease of cultivated mushrooms is the cause of extensive losses 

 to growers in this country, who state that unless precautions are taken 

 to prevent its spread it will necessitate the abandonment of the indus- 

 try in infected localities. 



The disease of cultivated mushrooms apparently is the same as that 

 which has caused great losses to foreign mushroom growers for many 

 years. 



This disease is caused by a fungus, a species of Mycogone, which has 

 two forms of spores, one possessing thin and the other thick walls. 

 Experiments prove that the thick-walled spores retain their vitality 

 under ordinary cultural conditions for considerable periods of time. 

 A moist atmosphere is essential for the growth of the fungus, as 

 moisture rather than heat favors luxuriant growth. Cultures kept 

 in a dry place were found to retain their vitality about 18 months. 

 This would indicate that under natural conditions the life of the spores 

 would be much longer. 



The removal of the diseased mushrooms as soon as they appear will 

 prevent the production of the thick-walled spores and thus lessen 

 the spread of the disease. 



