148 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



[Vol. 10 



The writer wished next to test the effect of light of reduced 

 intensity. Accordingly, 6 tubes containing sterile soybean 

 petioles were inoculated with strain 7, 6 with strain 11, and 6 

 with strain 14. The 18 tubes were then divided into 3 lots, 

 placing 2 cultures of each strain in each lot. Lot 1 was placed 

 in an undarkened covered glass dish; lot 2 was kept in a covered 

 glass dish lined with light-proof paper; and lot 3 in a similar 

 covered glass dish lined with sufficient waxed paper to reduce 

 the normal light intensity to approximately one-half. The 3 

 lots were kept on an open shelf between a north and a west window 

 of the laboratory where they received indirect light during the 

 day. The cultures were inoculated on June 12, and the first 

 examination was made on August 3. Lots 1 and 3 had formed 

 many pycnidia and were exuding pycnospores freely, while lot 

 , which had been kept in total darkness, had produced no 

 pycnidia. There was no obvious difference in the number or 

 state of development of pycnidia in cultures kept in full and in 

 reduced light. A light intensity of much less than half normal 

 apparently suffices to induce pycnidial formation when cultures 

 of Diaporihe Sojae are exposed continuously to it. 



In order to test the relation of length of exposure to normal 

 daylight to pycnidial production in cultures of the soybean 

 fungus, the following experiment was carried out : On September 

 7, 12 tubes containing sterile soybean petioles were inoculated. 

 The cultures were allowed to grow in complete darkness at room 

 temperature (20-30° C.) for 7 days. They were then divided 

 into 6 lots of 2 tubes each, and the different lots were exposed to 

 light for periods varying from to 60 hours of actual daylight 

 and then returned to darkness. The tubes which had been 

 exposed to 42 hours of actual daylight (72 hours of light and 



darkness) had already formed visible pycnidial initials when 



returned to darkness. The tubes were examined 10 days after 

 returning to darkness, and all had formed many pycnidia and 

 were exuding pycnospores. The shortest exposure was 14 hours. 

 In these cultures, pycnidia were fewer and somewhat less well 

 developed than in those exposed for longer periods. The tubes 

 were returned again to darkness, and when they were reexamined 

 on September 5, the pycnidia were about as numerous but were 



