1923] 



LEHMAN — POD AND STEM BLIGHT OF SOYBEAN 157 



concentrations by the addition of increasing amounts of lactic 

 acid produced in 10 days colonies of greater diameter on media 

 having a P H value of 4.5 than on the same medium with P H 3.8, 

 4, and 7.4, the 3 other values used. On the other hand, conidiai 

 production was 25 to 30 times greater at P H 3.8 than at 4. 



Maclnnes ('22) observed that a strain of Fusarium sp. isolated 

 from scabby wheat grew on a modified Czapek's solution at P H 

 values ranging from 3 to 11.7. No determinations were recorded 

 for H-ion concentrations immediately above these values. 



The writer has studied the growth of Diaporthe Sojae on a 

 nutrient solution containing inorganic salts and dextrose in the 

 following volume molecular concentrations: M/3.636 dextrose, 

 M/5 KNO„ M/20 KH 2 P0 4 , and M/100 MgSO*. Three drops 

 M/1000 of FeP04 were added for each 25 cc. of solution. The 

 dextrose was of the grade designated ' ' difco standardized M and the 

 inorganic salts were of Merck's "highest purity" grade except 

 the KHjPO*, the grade of which was "C.P." The nutrients 

 were dissolved in water which had been redistilled from glass. 

 After sterilization the solution was adjusted to the desired P H 

 values by adding previously determined amounts of sterile 

 0.5766 N H,PO< of 0.5031 N KOH. The quantities added 

 caused only inconsequential change in the molar concentrations 

 of the nutrients and did not alter total NO s and dextrose. The 

 P H values were determined by the colorimetric method of Clark 

 and Lubs ('17). The cultures were grown in 100-cc. Pyrex 

 flasks which had been treated with cleaning mixture and thor- 

 oughly rinsed in tap and distilled water. Twenty-five cc. of 

 solution were placed in each flask. Four days after the solutions 

 had been prepared, inoculations were made by introducing into 

 each flask a single pycnidium together with a small amount of 

 mycelium from a young culture on soybean petiole. The cultures 

 were kept at 25° C. in a dark incubator during the period of 

 growth. By use of a suction filter the mats were collected on a 

 filter-paper, the dry weight of which had been previously de- 

 termined. The mats were dried for 3 days in an electric oven 

 kept at 100-105° C, cooled in a HjSO* desiccator for a uniform 

 period, and weighed. After the filtrate from each mat had been 

 made up to 50 cc. by the addition of distilled water, the hydrogen- 





