60 



PLANT SUCCESSION AND CROP PRODUCTION 



feet, may be twenty days apart in the length of the growing season. 

 For example, at Milligan twenty-three years of frost records give 

 an average of 145 days in the growing season. Eighteen years 

 of records give Somerset 174 days. 



More important than the length of the growing season, how- 



23-5-2+5^ 



z^s:us/ 





«4 v5 -tSS 



MEAN EFFECTIVE HEAT 



MtPifS TE.MPE.R.,ATURX. A&OVt. 4Z.° rRJDM APRJL IS 

 TO OCTQCE-R. I aj 



Fig. 11 



ever, is a chart of the mean effective heat (Fig. 11). The data for 

 this chart were obtained through the kind cooperation of Mr. W. H. 

 Alexander, meteorologist and section director in the U. S. Weather 

 Bureau, who allowed the writer to examine the records on file in 

 the Columbus Weather Bureau office. The temperature normals 

 from all the weather observation stations in the state were ob- 

 tained and the average temperature from April to October found. 

 From this average 42 was subtracted, since 42° F. can be regarded 



