PROCEEDINGS OF THE OHIO ACADEMY OF SCIENCE. 257 



perature and rainfall constants during the development of the 

 plant, made by using the phenological data at Wauseon. Ohio, 

 shows that the most important period for temperature is for the 

 10 days following the date of blossoming. Cool weather is 

 necessary to insure a good crop. Rain is necessary during a 

 number of weeks before Ijlossoming. 



WEATHER AND WINTER WHEAT 



While most spring seeded crops, especially those of rapid 

 growth, have well defined periods when they are greatly alTected 

 by the weather, it is much more difficult to find the dominant 

 weather factor as well as the critical period of growth with fall 

 seeded crops or those with a long growing period. 



In connection with winter wheat, for example, the general 

 opinion is that particular weather conditions must have a great 

 effect upon the yield. Expressions like the following are com- 

 mon : "The weather of the fall was fine for the wheat crop." 

 "A poor crop of wheat will be harvested because the winter was 

 so severe." "It was so mild in January that a splendid wheat 

 crop is assured." 



Correlation coefficients have been calculated showing the 

 relation between the yield of winter wheat in Ohio and the 

 temperature and rainfall conditions, covering periods from 30 

 to 60 years. Some of these appear in table 9. 



Table 9. Correlation of the Yield of Winter Wheat in Ohio with 

 THE Temperature and Rainfall. 



Period. 



September 



October 



November 



December 



January 



February 



March 



April 



May 



Autumn (September to November) 



Winter (December to February) 



Spring (March to May) 



