228 Report of the Department of Botany of the 



In this experiment, the tubers designated as dry were cleaned by 

 dusting off the excess dirt, while the tubers designated as wet were 

 washed with water. Just previous to placing these potatoes in the 

 fumigator, the washed tubers were immersed in distilled water for 45 

 minutes, and then all excess water was wiped from the surface. The 

 80 pounds (equal to 3.7 pounds per cubic foot) of potatoes were 

 subjected for 24 hours to the gas evolved from a double quantity 

 of chemicals. Sclerotia of about the same size and texture were 

 used in making the cultures. As there was a slight leakage of the 

 gas from the fumigator these results are only comparative. Of the 

 40 sclerotia taken from the dry tubers, 22J per ct. developed 

 Rhizoctonia, while from the 50 moistened sclerotia but 2 per ct. 

 showed growth. This experiment indicates that the state of dessi- 

 cation of the sclerotia has an important bearing on the results of 

 fumigation. One would be led to believe that the humidity of the 

 atmosphere ought to have some effect on the efficiency of this gas, 

 but the data in Table I show no correlation between humidity 

 and efficiency. 



The data in Table III show that by the formalin dip method as 

 high as 64 per ct. of the sclerotia may still be alive after the treat- 

 ment, and an average of 8 tests shows that 24 per ct. of the sclerotia 

 were not killed. A longer period of immersion of the tubers gave 

 more satisfactory results than did a two-hour bath, but the deficiency 

 of the treatment can not be overcome by using a stronger solution. 



That the formaldehyde, when used in any form, did not kill 

 resistant spores of the potato bacillus when they were inside the 

 sclerotia or particles of soil, is shown where "agar, one per ct. acid" 

 was used as a culture medium. In fact, so prevalent was this 

 organism that it was impossible to make cultures unless additional 

 acid was added to the medium. That other fungi are not killed by 

 formaldehyde treatments when these organisms are inside of the 

 sclerotia is noted in Table I— III under the heading " other fungi." 

 Most of these fungi were species of Penicillium, but several were 

 uncommon or produced no spores, and no effort was made to identify 

 them. 



Where a solution of mercury bichloride of a strength of one part 

 of the salt to 1000 parts of water was used, there was no indication 

 of the growth of Rhizoctonia or of any other fungus or bacterium. 

 Even where half of the above amount of salt was used to a like 



