34 



SOME FUNGOUS DISEASES OF ECONOMIC IMPORTANCE. 



Table II. — Results of experiments with different quantities of formalin per 1,000 

 cubic feet of air space for 15 and 30 minutes, respectively, showing the increase 

 in the relative humidity of the atmosphere and the maximum percentage of 

 increase in the grains of moisture per cubic foot. 



Formalin 

 per 1,000 

 cubic feet. 



Temper- 

 ature be- 

 fore 

 mixing 

 reagents. 



Relative 

 humidity 

 before 

 experi- 

 ment. 



Relative 

 humidity 

 after 15 

 minutes. 



Relative 

 humidity 

 after 30 

 minutes. 



Increase in relative 

 humidity. 



Increase in grains 

 of moisture per 

 cubic foot. 



Increase 

 in grains 

 of mois- 

 ture per 

 cubic 

 foot. 



After 1.5 

 minutes. 



After 30 

 minutes. 



After 15 

 minutes. 



After 30 

 minutes. 



c. c. 

 900 .. . 

 1,000.... 

 1,100.... 

 1,200.... 

 1,300.... 



F. 

 76 

 78 

 76 

 76 

 76 



Per cent. 

 38 

 38 

 39 

 39 

 37 



Per cent. 

 51 

 53 

 53 

 56 

 54. 5 



Per cent. 

 50 

 50 

 51 

 54 

 51 



Per cent. 

 13 

 15 

 15 

 17 

 17.5 



Per cent. 

 12 

 12 

 12 

 15 

 14 



1.412 

 1.714 

 1.857 

 1.961 

 2.117 



1.236 

 1.395 

 1. 559 

 1.615 

 1.762 



Per cent. 

 38.50 

 43.88 

 49.30 

 52.88 

 57. 02 



CONCLUSIONS. 



It is demonstrated by the experimental evidence presented in this 

 paper that formaldehyde gas,, even in small quantities, exerts a retard- 

 ing action on the initial growth of Thielaviopsis paradoxa, while 

 with certain quantities it is fatal in its fungicidal effect. It will be 

 observed that in exposures to small quantities of the gas the results 

 were not always identical in like experiments and did not exhibit a 

 uniformity of gradation in periods of growth, although conditions, 

 temperature excepted, were duplicated. From constant and uninter- 

 rupted observation of the fungus under different degrees of tempera- 

 ture in gaseous and nongaseous atmospheres it is not believed that 

 these irregularities are due to differences in the temperature at which 

 the experiments were performed, but may be attributed to a variation 

 of the organism itself. Though the degree of retardation varies in 

 like experiments, as just stated, it is constant in being proportional 

 to the length of exposure in each set, 15, 30, and 60 minutes, respec- 

 tively. 



The quantity of gas fatal to Thielaviopsis paradoxa was obtained 

 by the use of 1,200 c. c. or more of formalin per 1,000 cubic feet of 

 air space. The proportions were used under varying degrees of 

 temperature, ranging from 65° to 80° F., but with fairly constant 

 humidity, the average being 38 per cent. The determinations were 

 made by the use of an air-tight compartment in which all the gas 

 was available and the fungus readily accessible to its fumes. Ex- 

 posures of 30 minutes or more were found to be effective. The 

 quantities of formalin ranging from 1,200 to 1,300 c. c. are the 

 maxima which would be employed in the commercial use of the gas, 

 since they were determined under most drastic conditions of tem- 

 perature and humidity. The temperature in pineapple-growing 

 countries would normally be above that under which some of the 



171 



