150 Journal of Agricultural Research voi. iv. no. 2 



several years will illustrate the point. A half-acre field was prepared. 

 Five pounds of pasteurized seed were sown on one quarter-acre and five 

 pounds of untreated seed on the other. As soon as the seedlings were 

 well out of the ground, examination was made for root sickness and 

 damping-off. No signs of damping-off were seen, but considerable root 

 sickness was in evidence on both the treated and untreated sections. 

 Cultures were started in the field by treating the seedlings for one minute 

 in a triturate of citric acid and bichlorid of mercury in water of such 

 strength as to give a i to 1,000 solution of sublimate. They were then 

 transferred to test tubes of sterilized water and were brought to the 

 laboratory, where they were plated. A period of 36 hours elapsed 

 between the treatment with the bichlorid of mercury and the plating. 

 From the untreated seed 95 seedlings yielded the following results : Phoma, 

 29; Fusarium, 19; Macrosporium, 2; Mucor, 6; miscellaneous, 18; no 

 growth, 21. From the treated seed 69 seedlings yielded : Fusarium, 23; 

 an unidentified ascomycete, 1 1 ; Macrosporium, 2 ; Mucor, 2 ; Penicillium, 

 i; miscellaneous, 8; no growth, 22. Phoma betae was not found in the 

 treated lot. The long interval before plating undoubtedly accounts for 

 the large amount of Fusarium and perhaps also for the failure to secure 

 growth in many cases. 



The average results secured from prompt plating may be seen from the 

 following series, which was from the same locality but was made two weeks 

 earlier. Many of these were plated immediately. Most of the Fusarium 

 resulted from seedlings which were carried in the water blanks for half a 

 day or more. Two hundred seedlings yielded cultures as follows : Phoma, 

 149; Fusarium, 29; Pythium, 3; miscellaneous, 11; no growth, 8. It 

 therefore appears that, while seed pasteurization rflay be employed suc- 

 cessfully to rid seed of Phoma betae for experimental purposes, it is not 

 applicable on a commercial scale. Moreover, such treatment does riot 

 guarantee freedom from physiological root sickness associated with sap- 

 rophytic fungi, since the vitality of the seedlings seems to be lowered by 

 pasteurization. 



A realization of these facts suggests the necessity of clean stock for 

 breeding purposes. It would seem that if the growers of elite strains 

 could rid their stock of this parasite it would thereafter remain clean, 

 provided a reasonable rotation were observed and the seed fields were 

 sufficiently isolated to escape reinfection with Phyllosticta. Danger 

 from this source would diminish with the increase in the supply of clean 

 seed. The experimental work already reported has shown the possi- 

 bility of eliminating the fungus from plants grown in isolation from pas- 

 teurized seed. These plants would produce clean seed which could again 

 be sown in isolation from infected stock and made the basis for a seed 

 supply for an entire community, from which the fungus would be elimi- 

 nated. This community could be employed as a breeding center where 

 the entire seed supply of a factory could be grown, and one of the most 



