Wire Stem of Cabbage 19 



comparatively. From a macroscopic and microscopic examination some 

 of them could apparently be identified conclusively, so that_ only six 

 different types remained for physiological studies. All strains could 

 hydrolyze starch and invert cane sugar. All showed increased growth 

 at a pH lower than 7.0, and all grew abundantly at 3.8. Four of the six 

 strains exhibited different minimum, optimum, and maximum temperatures 

 for growth. Their diastatic activity was unlike, and there was a striking 

 difference in the conversion of cane sugar. There were indications of 

 differences in the cellulase activity of the different strains. A difference 

 in the growth on casein, on peptone, and on asparagin was noted. Only 

 two strains could utilize potassium nitrite. All strains exhibited different 

 acid ranges. Fusion of hyphae was observed between some strains only, 

 and a striking difference in virulence was observed. It was noted that 

 greatest virulence was always manifest when inoculation was made on 

 plants belonging to the same host as that from which the culture originated. 

 Matsumoto concluded that there is a definite specialization among the 

 strains tried, but that all are forms of Rhizoctonia solani Kiihn except one, 

 which may have exhibited sufficient differences to be considered of specific 

 rank. This had been isolated from potato. 



Reviewing, then, the whole problem in the light of these investigations, 

 it is evident that the questions of biologic specialization needs further 

 study. It might be of value to observe here that of the investigators who 

 actually performed cross-inoculation experiments (Shaw, Sherbakoff, 

 Peltier, Edson and Shapovalov, and Matsumoto), none, according to the 

 evidence at hand, have inoculated cabbage seedlings with potato strains, 

 or have used the cabbage strain to inoculate potato plants. Sherbakoff 

 (1917a), working with but one strain from potato, may have conducted 

 such cross-inoculations, as he states that some strains were tried on cabbage, 

 cauliflower, cucumber, garden beans, and other plants, and proved able 

 to produce damping-off . 



Experimental data 



Early in his experimental work, the writer found indications of the 

 existence of specialization in the strains which he was using. In the 

 spring of 1921, twelve cabbage seeds were sown in each of twenty-seven 

 4- inch pots of sterilized soil. When the seedlings were two inches high, 

 they were inoculated by placing a bit of potato agar containing mycelium 

 at the base of the stem and covering lightly with soil. The plants in 

 six of the pots were inoculated with a strain from cabbage isolated the 

 previous summer; those in six others, with another culture isolated at the 

 same time; those in a third group of six, with a strain from potatoes from 

 Canada; and those in a similar group, with a strain from potatoes from 

 Maine. The remaining pots were kept as controls. Both the cabbage 

 strains produced 100 per cent damping-off and typical wire stem. Neither 

 of the strains from potatoes produced the disease. The checks likewise 



