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Journal of Agricultural Research 



Vol. XV. No. 3 



One field, which we may call field A (fig. 2), was on the southeast slope of 

 a hill and surrounded by trees so that it was well protected from wind, 

 especially northwest wind. Field B was on the west slope of another 

 hill and freely exposed to wind. The original centers of angular-leafspot 

 in B were on the north side near the top. Thunder showers on July 12, 

 16, and 19 were accompanied by high winds from the north and west. 

 On July 29 it was noted that in field A the infested areas were strikingly 

 more delimited than those in field B. The difference could be explained 

 only as a result of the difference in exposure to winds. 



Another field was situated on a freely exposed west slope, and its rows 

 ran with the hill, east to west. No notes on disease distribution there 

 were taken until August 4. On that date there was a center of abundant 



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Fig. 2. — Diagrams of cucumber fields to show relation of wind and drainage water to angtilar-leafspot 

 dissemination. Double circles indicate the location of original centers of infection prior to storms. 

 Small circles represent secondary infections due to storms. In field A drainage water only was an im- 

 portant factor because of protection from wind while in the freely exposed field B wind also played a 

 part. Contour Unes indicate elevation above level of Lake Mendota, Madison, Wis. Broken lines show 

 the direction of the rows. For full explanation see text. 



infection in the seventh row from the north side and scattered infections 

 in all of the 16 rows south of it. North of this badly infested area the 

 adjacent row, the sixth, showed a very small number of infections, and 

 the 5 others were entirely free from the disease. Obviously the northwest 

 winds had played an important part here also in spreading the disease. 

 Faulwetter (7) has shown that wind in connection with rain is an im- 

 portant factor in the spread of a similar bacterial disease, the angular- 

 leafspot of cotton. 



The fact that the thundershowers mentioned as resulting in a marked 

 spread of angular-leafspot occurred during the daytime supports the 

 inference which may be drawn from the facts regarding the relation of 

 stomatal movement to infection, that rains which occur in the daytime 

 are more effective in the spread of the disease than are those occurring 

 at night. 



