104 



JOURNAL OF ECONOMIC ENTOMOLOGY 



[Vol. o 



tr° ne" nf" tie' 107' lot* 



6?" a&' 



Fig. 2. Map of the United States showing the discrepancy between the theoretic 

 and actual date of safe-sowing in relation to normal annual precipitation. A = Actual 

 date of safe-sowing as determined by sowing experiments. T = Theoretic date of 

 safe-sowing figured according to "Hopkins' Law of Latitude and Altitude" from 

 the actual date of Columbus. 



differences between Ohio and the eastern Kansas series and between 

 the eastern and. western Kansas series, moisture stands out alone. 

 The following table well serves to bring out the existence of a ratio 

 between the difference existing betw^een theoretic and actual date of 

 safe-sowing and the difference in normal annual precipitation. The 

 ratio appears to be about one day to the inch — one day earlier if one 

 inch greater and one day later if one inch less. 



Correlation between Safe-sowing Date and Normal Annual Precipitation 



