30 SOME FUNGOUS DISEASES OF ECONOMIC IMPORTANCE. 



Experiment No. 29. 



1,200 c. c. formalin per 1,000 cubic feet of air space. 

 Temperature before mixing reagents, 70° F. 



Thielaviopsis spores suspended in water. 



Initial growth of 

 fungus. 



Micro- 

 spores. 



Macro- 

 spores. 



Check; fungus not exposed to formaldehyde gas 



Fungus exposed 15 minutes 



Fungus exposed 30 minutes 



Fungus exposed 60 minutes 



Hovrs. 

 29 

 

 

 



During the process of these experiments special attention was given 

 to the microscopic appearance of the spores before and after fumiga- 

 tion. No remarkable change was observed in the color, size, or 

 turgidity of the spores even when subjected to the gas generated from 

 formalin in quantities as high as 2,600 c. c. per 1,000 cubic feet of air 

 space. 



INOCULATION EXPERIMENTS. 



To determine what value fumigation may have in lessening or pre- 

 venting the loss of pineapples by Thielaviopsis, it is necessary to con- 

 sider the time and center of infection. Authorities differ upon this 

 subject, some contending that there is an incipient infection before 

 the fruit is pulled, others that infection takes place at the exposed cut 

 portion of the stem or at points of mechanical injury. The last two 

 possibilities presuppose the fact that the spores being abundant on 

 the plant in many instances find a resting place on the fruit. Cul- 

 tures of the fungus obtained from sound market fruit with super- 

 ficially adhering spores indicate a strong probability of this condi- 

 tion. In order to determine what effect the formaldehyde gas might 

 exert on spores superficially present on the fruit or in various stages 

 of development, the following experiments were made. Pineapples 

 were inoculated by pure cultures of the fungus being introduced into 

 six separate incisions. The fruit was then kept in a warm, damp, and 

 dark atmosphere for forty-eight hours, at the expiration of which it 

 was subjected to fumigation. Just previous to the treatment a few 

 spores were taken from the inoculated points and cultures started as 

 checks for the transfers made from inoculated points after fumiga- 

 tion. 

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