12 



BULLETIN 127, U. S. DEPARTMENT OF AGRICULTURE. 



weight U. S. P. standard). The formahn-permanganate method was 

 used to generate the gas in all the experiments, since it has been 

 found that it is the only practicable way of using the gas in mushroom 

 houses. By this method formalin is poured on crystals of potassium 

 permanganate, and this was the procedure in the laboratory experi- 

 ments, but in the practical application of the method it was found 

 necessary to deposit the potassium permanganate in the receptacles 

 containing the formalin. Chemically pure potassium permanganate 

 in finely divided crystals was used. In each of the experiments the 

 proportions were 100 cubic centimeters of formalin to 50 grams of 

 potassium permanganate. 



Exposures of Cultures. 



In the laboratory experiments, pure cultures of the fungus were 

 subjected to the direct action of the formaldehyde gas. The cultures 



were exposed to the gas 

 in Petri dishes and 100- 

 cubic-centimeter flasks. 1 



Transfers for checks 

 were made from the cul- 

 tures to be subjected to 

 the action of the gas im- 

 mediately before the fumi- 

 gation and again imme- 

 diately after fumigation, 

 in order to determine the 

 effect of the formaldehyde 

 gas on the vitality of the 

 fungus. Figure 4 shows 

 the manner in which the 

 inoculations were made in 

 every case in Petri dishes. 

 There were four centers 

 of inoculation, and the 

 amounts transferred from 

 the fumigated cultures were large enough to allow abundant chance 

 for the fungus to grow. In the flask cultures four inoculations were 

 also made. 

 Results op Fumigation with Formaldehyde on Cultures of the Fungus. 

 The results of these experiments are given in Table I. The efficacy 

 of formaldehyde in destroying the parasite is clearly shown by these 

 experiments. As stated by McClintic (1906), and also by Patterson, 

 Charles, and Veihmeyer (1910), it seems that higher temperature and 

 humiditv increase the fungicidal action of the gas. 



Fig. 4.— Check culture, experiment 5: Transfer made from 

 culture before it was subjected to formaldehyde gas. 

 From a photograph made 189J hours after inoculation. 



i The cultures contained Mycogone and Verticillium. as in no instance was it possi 1 le to cultivate the 

 Verticillium alone. 



