24 Levi Otto Gratz 



was used to inoculate cabbage seedlings at different times. Negative 

 results were consistently obtained. The cabbage strain under the same 

 conditions produced 100 percent of damping-off, and the checks remained 

 healthy. To further test this particular strain, seedlings were inoculated 

 as follows: two rows on one end of a flat were inoculated with the cabbage 

 strain, and two rows on the other end with the aster strain. The three 

 rows at the center served as controls. The center rows and those inocu- 

 lated with the aster strain remained healthy. Of the plants inoculated 

 with the cabbage strain, 80 per cent damped-off. Therefore the aster 

 strain tested here is not pathogenic on cabbage. Inoculations on asters 

 at this time demonstrated that the strain is pathogenic on that host. 



In a study of the question as to whether or not the strains freshly isolated 

 from potato tubers are pathogenic on potatoes, the following experiments 

 were performed. Tubers of the Bliss Triumph variety, treated with cor- 

 rosive sublimate as before, were planted in the temperature tanks (page 26,) 

 where both the temperature and the moisture of the soil could be con- 

 trolled. Richards' (1921, 1923) strain of Corticium vagum could infect 

 potatoes at a wide range of temperature, 9° to 27° C, with the optimum 

 near 18°. The optimum for the host was about 24° C. In view of these 

 facts, the soil temperature was maintained at 22° in order to hasten ger- 

 mination but still remain within the range of infection. The moisture 

 content of the soil was maintained at about two-thirds of its water- 

 holding capacity. Sterilized soil in glazed earthenware gallon jars, meas- 

 uring 19 by 19 centimeters, was used in all cases. One seed piece was placed 

 in each jar, and five jars were used for each strain and twenty-five jars 

 for each tank. One set of five jars was inoculated with the cabbage strain 

 as a check on the previous experiment (table 8). The inoculum was placed 

 around the seed piece and in the same plane as the upper surface of the 

 tuber, to insure the contact of the sprout with the fungus. When the 

 plants were three inches high, 70 per cent of all the stems inoculated with 

 the potato strains had distinct lesions. All the strains tested were path- 

 ogenic, each producing lesions on from two to five of the five stems inocu- 

 lated. Wounding and reinoculating the uninjured stems increased the 

 total number of injured stems to 80 per cent. The initial inoculation with 

 the cabbage strain gave negative results, and a reinoculation after wound- 

 ing produced slight discoloration on three stems. It is not positive that 

 this discoloration was caused by the fungus, as these lesions became no 

 more pronounced after ten days. In a second tank, maintained at exactly 

 the same temperature and moisture conditions, twenty-five tubers were 

 inoculated with the cabbage strain as before. Here three stems developed 

 small, superficial, apparently positive lesions, but these failed to develop 

 further. All the stems, except the three mentioned, were wounded and 

 a large amount of inoculum was pressed tightly against the wound, but no 

 further lesions developed. Again, it is doubtful whether the cabbage 

 strain caused these lesions. In a third tank, where the soil temperature 



