. 



1923] 



LEHMAN — POD AND STEM BLIGHT OF SOYBEAN 167 



(7) The causal organism overwinters on diseased stems and in 

 diseased seed. Pycnospores are produced in abundance in the 

 spring on diseased stems which have lain in the field over winter. 

 Diseased seed have yielded isolations of the causal fungus in 

 April and May following the season in which they were grown. 



(8) Black Eyebrow is apparently more susceptible than any 

 of the other varieties observed. 



(9) Infection and dissemination of this disease during the 

 growing season is strongly dependent on relatively high humidity, 

 the disease being markedly more abundant during rainy than 



during dry summers. 



(10) The fungus has been grown in culture on a variety of 

 substrata. In general, pycnidia are not formed numerously on 

 agar media, cooked rice, or potato plugs. They are produced in 

 large numbers on sterile soybean stems and petioles and on stems 

 of Melilotus alba. Perfect strains produce perithecia on all 

 media on which pycnidia are formed abundantly. 



(11) In a nutrient solution containing inorganic salts and 

 glucose, pycnospores germinate over a wide range of hydrogen- 

 ion concentrations. The lower limit for germination lies between 

 P H 2.2 and 3.0 and the upper limit beyond 8.6. The range 

 P H 4.1-6.1 is apparently optimum for germination. 



(12) Certain changes occurring during growth of mycelium 

 in a nutrient solution containing inorganic salts and glucose have 

 been followed. Growth was nil at P H 1.8 and 2.2, and extremely 

 slow at 2.5. Growth starting at P H 3.1 was much slower than 

 at P H 4.0, but dry weight of mat produced at the former value 

 nearly equalled that attained in the latter. Maximum growth 

 occurred in the series started at P H 4.0 Good growth occurred 

 in the series started at P H 8.9 but was slower a id notably less in 

 amount than in the series started at 8.7. Sugar disappeared 

 from the solution concomitantly as the weight of mat increased. 

 All sugar had disappeared from the culture solution when 

 maximum growth had been attained. Changes in reaction of 

 the culture solution occurred during growth. Cultures initially 

 acid steadily became less so, and cultures originally alkaline 

 first became less alkaline, then reversed the direction of change 

 and became more alkaline than at the start. 





