1923] 



LEHMAN — POD AND STEM BLIGHT OF SOYBEAN 153 



from a culture 140 days old. However, pycnospores are usually 

 no longer viable when the culture has attained this age. 



Bright diffuse daylight exercises no apparent influence on 

 germination of pycnospores in tap water. In a number of tests 

 in which spores from the same source were germinated in light 

 and in darkness, approximately equal germination occurred. 



Since the introduction of convenient and accurate methods 

 for the determination of active acidity, certain workers have 

 recorded their observations relative to the effect of the concen- 

 tration of H and OH ions upon germination of fungous spores. 

 Webb ('19, '21), using 8 different fungi and different types of 

 media, found that the amount and range of germination as 

 influenced by H-ion concentration varied with the organism 

 and the medium. The greatest number of fungi employed 

 exhibited maximum germination between P H 3.0 and 4.0, the 

 percentage of germination decreasing rapidly at higher, and less 

 rapidly at lower, concentrations of H ions. Fusarium showed 

 marked tolerance, and C olletotrichum Gossypii favorable response, 

 to alkaline reaction of the culture medium. Hursh ('22), working 

 with urediniospores of 2 biologic forms of Puccinia graminis 

 Tritici, found marked differences in the germination quantities 

 at the same H-ion concentrations over the greater part of the 

 range where germination occurred . These differences were much 

 greater at temperatures of 10 and 30° C. than at 20° C. The 

 range indicated was approximately P H 2.5-8.0, and best ger- 

 mination occurred between P H 4.5 and P H 6-7. Maneval ('22) 

 found that teliospores of Puccinia Helianthi will germinate in 

 solutions having a range of H-ion concentrations represented by 

 the P H values 3.5-8.4. However, the limits for very good 

 germination and good sporidial production were approximately 

 P H 4.6-6.5. 



The writer tested the effect of H-ion concentration on the 

 germination of pycnospores of Diaporthe Sojae in a synthetic 

 solution consisting of inorganic salts dissolved in distilled water 

 in the following volume molecular proportions: M/5 KNO», 

 M/20 KH.PO,, and M/100 MgS0 4 . Three drops of M/1000 

 FePO* were added to each 25 cc. of solution. The desired H-ion 

 concentrations were obtained by adding previously determined 



