Oct 8, 1921 Temperature and Humidity Studies of Fusaria Rots 73 



been kept in cold storage from the previous year. The experiment was 

 conducted in the same way as experiment 4, and the same cultures of 

 Fusarium oxysporum, F. trichothecioides , and F. radicicola were used for 

 inoculations. Only two temperatures were used, 13.5° and 25° C, as 

 well as two humidities, 33 and 100 per cent at each temperature. The 

 results shown in Table III were taken after six weeks. 



As in experiment 4 the rotting was much greater at the high tempera- 

 tures and the high humidities. At the lower temperature of 1 3.5 ■^ C. there 

 was no distinct difference between the amount of rotting in the old and 

 new tubers, due to the very slight penetration at this temperature. In 

 the old tubers at 25° the infection in every case had been rapid and the 

 rotting had progressed much further than in the new tubers. These 

 results support the statement of Bisby (j) that old tubers are more sus- 

 ceptible to rot than new tubers. 



Table III. — Extent of penetration of old and new tubers 



Experiment 5, 19 15. — The results of earlier experiments having 

 indicated that the influence of the relative humidity was nearly as great 

 as that of temperature, it was decided to run a more complete test on 

 the effect of the relative humidities at different temperatures. Since 

 no apparatus was available by which the relative humidity and tempera- 

 ture could be controlled at will, it was necessary to construct one. 



The principle employed in experiment 4 of using sulphuric-acid solu- 

 tions of varying specific gravity in a closed chamber to obtain the different 

 relative humidities was not used in this test. In preliminary experi- 

 ments conducted in the same way as experiments 4 and 4A, the infection 

 usually resulted in a softrot which gave good comparative results, but 

 the type of rotting was not similar to that usually found in storage. 

 Cultures from these softrots invariably yielded the Fusarium sp. used 

 in the inoculation, and no bacteria were present in any case. Apparently 



I 



