Apr. 3, 1916 



Climatic Conditions and Cercospora beticola 



51 



the probably higher humidity of the former. Only during a very favor- 

 able period (fig. 7, July 19 to 21) or where the leaves were turned up or 

 protected by other leaves was the conidial production on the upper 

 surface equal to that on the lower surface (fig. 8, series E, July 21). At 

 times, conidia were formed more abundantly on the upper surface than on 

 the lower (fig. 6, series N, August 11, and series S, August 28). Because 

 of the spongy parenchyma and the greater number of stomata on the 

 lower surface, it might be supposed that conidiophores could be produced 

 more readily on this than on the upper surface; but, as above indicated, 

 humidity would seem to be the controlling factor in this connection. 



S-'^ 



•\% 



\ % '\i ^ \ ^ 



Fig. 7. — Curves of the maximum and minimum temperatures and humidities, the number of hours that the 

 humidity remained above 60 from noon of the preceding to noon of the given day among the plants, 

 and rainfall and irrigation records, taken in a medium-early sugar-beet field from June 10 to September 

 22, 1913, at Rocky Ford, Colo. 



A comparison of the conidial production as shown in Table IV and 

 figure 6 and the climatic data shown in figure 7 indicates many definite 

 relations. When the spots were first found, on June 20 and 24, conidia 

 were fairly numerous (fig. 6, curve A) on all except six spots, which had 

 evidently just developed on the latter date, as no conidia were present 

 at this time and conidiophores only were produced the next two weeks. 

 The following week there was but little increase, and during the next few 

 days many of the conidia were disseminated. The small production of 

 conidia was evidently due directly to the high temperature and the low 

 humidity which prevailed during this period (fig. 7), as conidia were pro- 

 duced in great abundance from July 9 to 12 (fig. 6, curves C, D, E, F), 

 when the temperature was lower and the humidity higher (fig. 7). Dur- 



