yo Journal of Agricultural Research voi. xxn.No a 



25° C. The characteristic rot under these conditions is a soft we trot with 

 no sharp line of demarkation between the healthy and diseased tissue. 

 The organism appears to be unable to attack whole starch grains, which 

 accumulate in a granular mass with the myceliimi, as in set 2. The 

 tuber-rot under these abnormal conditions is not typical of the rots 

 usually found in storage. 



Experiment 2, February 23, 1916. — Further tests were conducted at 

 the same temperature but with a lower relative humidity to test the abil- 

 ity of the organism to cause a rot under conditions not so adverse for the 

 host as in the previous experiment. Tubers of the Up-to-Date variety 

 were inoculated by wounding and then placing a little of the fungus 

 mycelium and spores in the wound. The tubers were then placed in a 

 sterile moist chamber but were not wrapped in paper. Controls were 

 treated and wounded in the same way. The experiment was run at 25° 

 C. Twelve different strains of Fusarium oxysporum were used for the 

 inoculations, two tubers being used for each strain. Results were taken 

 after five weeks. 



In only one case had the rot extended three-fourths of the length of 

 the tuber. In all the other tubers there was only a slight rotting extend- 

 ing for a short distance from the point of inoculation. The controls 

 remained sound in every case. The tubers were in a saturated atmos- 

 phere at the beginning of the experiment, gradually becoming drier until 

 at the end the tubers were considerably dried out. Compared to the 

 preceding test the amount of rotting was very slight, and its inhibition 

 may be directly attributed to the dryness of the air. The slight amount 

 of rot around the point of inoculation would indicate that the fungus 

 progressed a short distance into the tuber at the beginning of the experi- 

 ment when the humidity was high but was unable to advance further 

 under the drier conditions. This would indicate that the rotting of 

 tubers already started could be checked by submitting the tubers to 

 lower humidities. 



Experiment 3, April, 26, 1916. — A further test on the relation of 

 humidity of the atmosphere to the rot of the tuber was started. The 

 inoculations were made as in the previous experiment, and the same 

 variety of potatoes was used. 



Set No. I. The inoculated tubers were placed in sterile chambers, and 

 moist filter paper was placed in the chambers at the start of the experi- 

 ment to produce a favorable humidity for the initial penetration of the 

 tuber. 



Set No. 2. The tubers were placed in moist chambers in which the 

 atmosphere was kept saturated throughout the experiment. 



Both sets were kept at a temperature of 25° C. The results were taken 

 after seven weeks. (Table I.) 



