1923] 



LEHMAN — POD AND STEM BLIGHT OF SOYBEAN 149 



obviously less well developed in the cultures exposed for 14 hours 

 than in those subjected to light for longer periods. 



A second test much like the one described above was started 

 on October 1. The cultures were allowed to grow at room 

 temperature (about 20° C.) for a period of 8 days in total darkness 

 in a large covered tin box kept in a dark desk. Different lots 

 were then exposed for periods of time varying from 6 to 36 hours 

 of actual daylight and then returned to darkness. The tubes 

 which had been exposed to 36 hours of daylight already bore 

 numerous visible pycnidial initials when returned to darkness. 

 The cultures were examined on October 29, and at this time all 

 except the checks bore numerous pycnidia, mpny of which were 

 exuding spores. The shortest exposure was 6 hours and in these 

 cultures the pycnidia were not appreciably less numerous nor 

 less well developed than in the tubes exposed to light for longer 

 periods. During the period of the shortest exposure, namely, 

 6 hours, the sky was so cloudy that the normal light intensity 

 was less than one-half that of normal daylight. The checks, 

 which had never been exposed to daylight, developed no pycnidia 

 even though they were continued in darkness until December 6. 

 Obviously, light is essential for pycnidial production in cultures 

 of Diaporthe Sojae. However, daylight of less than half normal 

 intensity acting for a period no longer than 6 hours suffices to 

 stimulate pycnidial development and spore formation. This is 

 in accord with the findings of Coons ('16) who reports the for- 

 mation of a small number of pycnidia in cultures of Plenodomus 

 fuscomaculans exposed for 2 hours to strong indirect light. 



The writer wished to try the effect of artificial light on pycnidial 

 production. This was done in a rather crude way by the follow- 

 ing experiment. Four cultures on sterile soybean petioles were 

 enclosed in a white glass Mason fruit jar and 4 similar cultures 

 were kept in a card-board box provided with a screw top to ex- 

 clude light. These two lots of cultures were kept in an incubator 

 at a distance of one foot from a 50-watt Mazda lamp. Since the 

 lamp was being used as the heating element for the incubator, it 

 burned intermittently. The cultures remained in the incubator at 

 28° C. during the entire time of the experiment, but the total 

 time of actual illumination was less than half this period. At 



