10 Levi Otto Gratz 



indicators previously prepared. The medium of each fiask was poured 

 into petri dishes before the adjustment of the next flask was begun. This 

 method is particularly satisfactory because the dangers of contamination 

 are reduced to a minimum, and because it permits large numbers of repli- 

 cations on media of exactly the same pH value. 



In a preliminary experiment performed as described, with the exception 

 that lactic instead of hydrochloric acid was used for acidi/ication , it was 

 demonstrated that the minimum and maximum pH values for four differ- 

 ent strains of the fungus were beyond 2.4 and 8.5, respectively. The 

 optimum was not sharply defined. Considerable variation was in evidence, 

 both within each strain and between the different strains. 



In a subsequent experiment the same strains were compared, and the 

 above-mentioned aster strain also was included. Considerable variation, 

 due to some unexplained factors, again resulted. This experiment, how- 

 ever, clearly demonstrated that the maximum and the minimum were a 

 little above and a little below pH 10.0 and 2.4, respectively. Again the 

 optimum was not sharply defined. 



In a third trial, both the old 1920 culture and the freshly isolated 1923 

 culture of the cabbage strain were compared with the aster, the bamboo, 

 and the six potato strains. In this experiment the acid limit was reached 

 for all the strains, but for neither strain was the alkaline limit definitely 

 demonstrated (table 3). The rate of growth for the cabbage strain at 

 the different pH values for five days is illustrated in Plate II. Consider- 

 able variation was again exhibited by the same strains at the different 

 values. In general, the growth rate increased with an increase in pH up 

 to a definite value, but rather frequently a plate of higher pH would show 

 less growth than the one immediately below (table 3). A more sharply 

 defined difference, however, was that of the tolerance of the various 

 strains to acid media. The strain from bamboo was definitely more 

 tolerant than any of the others, as it produced a mycelial growth one 

 centimeter in diameter in four days at pH 2.0. The strains from potato 

 tubers produced less growth, consistently, than either the cabbage, the 

 bamboo, or the aster strain at this hydrogen-ion concentration (table 3). 

 The color of the mycelium at these high acidities was white, so that it is 

 not evident in the photographs of the petri dishes. By comparing table 

 4 and Plate III, it will be observed that at pH 2.4, the mycelium of both 

 the cabbage and the aster strain completely covered the petri dish in 

 twelve days. The potato strain (P 27) had covered an area of small 

 diameter, almost completely covered with sclerotia, while the bamboo 

 strain was a fluffy mass of white mycelium with minute sclerotia scattered 

 over the surface of the petri dish (Plate III). At a pH of 2.7, similar 

 results were again obtained. Here one of the potato strains (P 70) had 

 covered an area of only 2.6 centimeters in diameter, while practically all 

 of the other strains had covered the petri dishes (Plate IV). 



