Oct. 8,1921 Temperature and Humidity Studies of Fusaria Rots 71 



Table I. — Comparative amount of rot produced by Fusarium spp. under different con- 

 ditions of relative hum,idity 



In all cases where rotting was present the starch grains were not 

 corroded. Culture No. 8 seemed to have a much slower initial growth 

 than the others, thus showing a greater difference between the two sets. 

 In general, it can be clearly seen that the rotting was much greater in 

 set No. 2, where the atmosphere was saturated throughout the experi- 

 ment. Although the organisms were capable of starting a rot under the 

 moist conditions at the start of the experiment in set. No. i, they were 

 later considerably checked imder the drier conditions. 



Experiment 4, March 15, 19 17. — Further infection experiments were 

 started under conditions in which the relative humidity of the atmosphere 

 was controlled by the use of various concentrations of sulphuric acid. 

 Previous experiments conducted at the Michigan Agricultural Experi- 

 ment Station in 19 15 and described under experiment 5, in which the 

 relative humidities were carefully controlled, produced very good results 

 with Fusarium oxysporum. 



The apparatus used in experiment 5 was not available in 191 7, so the 

 relative humidities used in experiments 4 and 4A were determined from the 

 tables given by Stevens (aj). One-quart Mason jars were used, in which 

 were hung small wire baskets containing the tubers, the acid being placed 

 in the bottom of the jar. Tubers of the Rural New Yorker variety were 

 inoculated as in the preceding experiments. They were then placed in 

 the baskets in the sterilized jars and were sealed with paraffin and placed 

 at the desired temperatures. The experiment was run in duplicate. 

 Three strains of Fusarium oxysporum, two of F. trichothecioides , and one 

 of F. radicicola were used for the inoculations. The temperatures used 

 were 5°, 9°, 16°, and 25° C. While these temperatures varied somewhat 

 during the experiment, the extremes did not in any case overlap. The 

 relative humidities obtained by using sulphm-ic acid remained fairly 

 constant throughout the experiment. One hundred cc. of each of the 

 acid solutions were used for each jar. At the close of the experiment the 

 specific gravity of the solutions was taken, and the calculated humidity 

 at this time was compared with that at the start, with the result that the 

 one having 1.5 per cent relative humidity had changed to 3.6 per cent, 

 the 33 per cent to 49 per cent, and the 66.5 per cent to 74 per cent. These 

 variations were not considered great enough to cause conflicting results. 



