Wire Stem of Cabbage 25 



fluctuated between 15° and 19° C, twenty seed pieces were inoculated with 

 potato strains and five with the cabbage strain. The sprouting of the tubers, 

 as compared with those in the other tanks, was delayed a week or ten days 

 because of the low temperature. For the same reason, the initial inocu- 

 lation produced infection on only 25 per cent of the stems. Various meth- 

 ods of reinoculation were attempted, resulting in lesions on 65 per cent of 

 the stems. No lesions were produced by the cabbage strain. In this trial 

 many sclerotia were produced on the rootlets and even on the stems. Both 

 the potato and the cabbage strains produced sclerotia in abundance on 

 their respective hosts, but were never observed to do so on the opposite 

 host. When the cabbage seedlings were inoculated with the potato strains, 

 the soil and the base of the stems were frequently covered with the fungus 

 mycelium, but neither sclerotia nor lesions were observed. 



A total of 230 inoculations of potatoes were made with thirty-two 

 strains of the fungus freshly isolated from potatoes, and nineteen of these 

 strains were definitely pathogenic. The remaining thirteen likewise might 

 have proved pathogenic had the temperature been more favorable. These 

 negative results were obtained when the soil temperature fluctuated 

 between 22° and 25° C, a temperature too high for the rapid development 

 of the disease (Richards, 1923). This was demonstrated by inoculating 

 potato stems at these higher temperatures with strains previously proved 

 to be pathogenic. Under such conditions these likewise produced no 

 lesions. Parallel with the above-mentioned inoculation experiments, 

 sixty-five tubers were inoculated with the cabbage strain and placed under 

 these controlled conditions. No definite lesions developed, demonstrating 

 the non-pathogenicity of this strain on potatoes. In the light of the 

 hundreds of inoculations on cabbage seedlings with the pathogenic strains 

 isolated from potatoes, and the large number of inoculations on potatoes 

 with the cabbage strain, all under more or less favorable conditions, 

 it must be concluded that a specific pathogenicity exists. 



Longevity of the fungus in the soil 



Little is known concerning the actual length of time that this fungus 

 will persist in the soil. Since it is parasitic on a considerable number of 

 plants, the possibility is that it may live in the soil indefinitely. Further, 

 the organism is saprophytic on the organic matter in the soil (Rolfs, 1902, 

 1904), and the richer the soil is in humus, the more favorable are the 

 conditions for its development. When the investigations on this problem 

 were discontinued at the approach of the summer season in 1921, the pots 

 containing the fungus-infected soil were placed under the greenhouse 

 benches and permitted to completely air-dry. The following fall this 

 soil was thoroughly mixed and cabbage seed was planted in it. The 

 same procedure was followed also with the soil that was used the second 

 year. In both seasons the percentages of diseased plants were approxi- 



