THE MYCOGONE DISEASE OF MUSHROOMS AND ITS CONTROL. 11 



ing drab in the center and finally light brown. As the method of 

 growth is centrifugal and the marginal growth of the culture is the 

 youngest, it is the last to become brown. The most important 

 physical factor concerned in the growth of the fungus in culture 

 proved to be humidity. While ordinarily low temperatures are not 

 conducive to the growth of fungi, in the present instance it was found 

 that a moist atmosphere was more important to the growth of the 

 cultures than a high temperature. This observation was made from 

 the study of numerous cultures in flasks and tubes and on various 

 media subjected to different degrees of humidity maintained at 

 various temperatures. Cultures grew at a temperature as low as 

 2° C. (35.6° F.) when considerable moisture was present, while cul- 

 tures at a temperature 

 of 35° C. (95° F.) in a 

 dry atmosphere failed 

 to produce any growth. 

 This peculiarity of the 

 fungus is an important 

 factor in the method of 

 fumigation. 



Treatment with Formal- 

 dehyde Gas. 



In view of the impor- 

 tant role of formalde- 

 hyde as a disinfectant 

 and fungicide and the 

 success obtained from 

 its use in inhibiting the 

 growth of certain para- 

 sitic fungi (Patterson, 

 Charles, and Veih- 

 meyer, 1910), a series of laboratory experiments was performed 

 to determine the effect of formaldehyde upon the Mycogone disease 

 of cultivated mushrooms. 



The apparatus used in these experiments is fully described and 

 illustrated in Bulletin No. 171 of the Bureau of Plant Industry. It 

 consists of a large air-tight box provided with a glass door and a set 

 of drawers, whereby cultures can be withdrawn from the box at any 

 time during the process of fumigation with a minimum loss of the 

 formaldehyde gas. 



Chemicals Employed. 



The formalin employed in these experiments was purchased in the 

 open market and was supposed to be of full strength, which should 

 contain 40 per cent by volume of formaldehyde gas (37 per cent 



Fig. 3. — Petri-dish culture of Mycogone on com meal, 211 J hours 

 after inoculation made from an infected mushroom. 



