Apr. 3, 1916 Climatic Conditions and Cercospora beticola 57 



Prior to August i , only isolated records of humidity were made in the 

 early field,^ but after this date continuous records of both humidity and 

 temperatures in both fields were available for comparison (fig. 10).^ 

 The temperatures prevailing in the two sugar-beet fields were quite com- 

 parable, but the humidity was generally different. For instance, from 

 August 2 to 23 the humidity remained above 60 for a longer time, and 

 the maximum humidity was, as a rule, higher in the early than in the 

 medium-early field; from August 23 to September i the maximum 

 humidity was lower in the early than in the medium-early field; after 

 the latter date strikingly lower, the difference ranging from 5 to 1 5 units ; 

 after September 5 the humidity remained above 60 for a shorter time 

 in the former than in the latter field; but from September 6 to 21 the 

 range of humidity in the two fields was much closer than during the 

 periods previously mentioned. 



The difference in the humidity of the two fields seemed to be due to 

 the difference in the amount of foliage present. Early in the experiment 

 the foliage was heavier in the early than in the medium-early field, but 

 owing to an extremely severe infection, which developed between July 

 29 and August 13 (fig. 9), the relative proportion of foliage in the two 

 fields was reversed after that period. As a result of this reversal, less 

 moisture was retained and the humidity was lower in the early than in 

 the medium-early field during September, and consequently at that time 

 the relative increase in infection was less in the former than in the latter. 

 Speaking more specifically, early in the experiment there was an aver- 

 age of 29 functional leaves per plant in the early field and 22 in the 

 medium-early; on August 15 there was an average of 26 leaves per plant 

 in both fields, while later on there were fewer per plant in the early 

 than in the medium-early field. On the other hand, on August 13 there 

 was an average of 23.5 infected leaves per plant, with an average of 710 

 spots per leaf in the early field, and on September 8 there was an average 

 of 21.5 infected leaves per plant, with an average of 508.3 spots per leaf, 

 in the medium-early field. 



A comparison of the death rate of the leaves in the two fields before 

 and after the disease appeared shows its destructiveness. For instance, 

 in the early and medium-early fields, from July 7 to 29 and from July 2 

 to August 25, when no leaves were killed by the fungus, the death rate 

 from normal causes was approximately one leaf per plant in three and 

 four days, respectively; while from July 29 to August 15 and August 25 

 to September 19, when the disease was most severe in the two fields, the 

 death rate averaged one leaf per plant in nine-tenths of a day and one 

 and three-tenths days, respectively. 



1 These and the later continuous records indicate that prior to August i the humidity was generally 

 higher in the early than in the medium-early field. 



* The temperature records taken at the Weather Bureau station were included in the comparisons and 

 were found to agree closely with those obtained in the two fields. 



