150 Journal of Agricultural Research voi. vi. No. 4 



in pure culture. In endeavoring to obtain such cultures, the following 

 procedure was adopted. Several watermelons were selected in which 

 the decay was just beginning to be apparent. A razor was flamed; 

 and with this, a funnel-shaped section, which included a portion of 

 both diseased and healthy tissue, the two being separated by a more or 

 less distinct line of demarcation, was cut from the melon. After the 

 razor had been flamed again, the section was divided along the line of 

 demarcation which distinguished the advancing edge of the decay, the 

 plug being cut from the inside toward the outer surface. This gave 

 access to a portion of the rind to which the fungus filaments were proba- 

 bly just advancing and which would be unlikely to contain concomitant 

 forms. From this region, using a sterile platinum needle, small portions 

 were removed from just below the surface and placed directly on syn- 

 thetic agar in sterile Petri dishes. After two days, during which the 

 plates were kept at a temperature of 27° C, an abundant mycelial 

 growth of a gray color appeared in every instance. A number of trans- 

 fers of the mycelium thus obtained were made to potato cylinders, and in 

 all cases a fungus developed which possessed the characteristics of the 

 genus Diplodia. In order to test the capacity of this organism for pro- 

 ducing the decay, the pure culture was inoculated into a sound water- 

 melon at three widely separated points, at each of which the character- 

 istic rot was reproduced. 



The direct connection between this fungus and the disease having 

 been thus indicated, 16 healthy watermelons were obtained for more 

 inoculations. They were bought at the wharf in Washington, D. C, 

 and came from the Pyankatank River district in Virginia, a region free 

 from the disease, so far as is known. It may be well to mention in this 

 connection that the decay has usually been reported as occurring on 

 the variety known as " Tom Watson." This is probably due to the 

 fact that in the last few years this melon has been grown somewhat to 

 the exclusion of other varieties. Of the melons chosen for inoculation, 

 three were "Excel" melons; the remainder were of the "Tom Watson" 

 variety. 



These melons were placed on a table near a large window which was 

 kept open the greater part of the day, and were protected from the 

 direct light of the sun by a cardboard screen. For a period of nine 

 days, during which time the melons were under observation, the average 

 temperature was 26.5° C. Of these 16 watermelons, 8, two of which were 

 of the "Excel" variety, were inoculated with the fungus, the cultures 

 used in this case having been derived from the original subculture. 

 This was accomplished by making with a sterile knife at a single point 

 near the stem an incision, into which a bit of the growing fungus mycelium 

 was introduced. A similar wound was made in the remaining 8 melons, 

 including the third "Excel" variety, but no infectious matter was 

 introduced. Within 36 hours the 8 inoculated melons began to show 



