348 



Journal of Agricultural Research 



Vol. XX, No. 5 



plots from 1913 to 1918. Possible exceptions are ear corn in 191 5 and 

 silage corn in 191 8, for which the correlations are positive and perhaps 

 statistically significant in comparison with their probable errors. The 

 correlations for yields of sugar beets in 191 1 and yields of barley in 1919 

 are negative in sign and apparently statistically significant in compari- 

 son with their probable errors. We have no explanation to offer con- 

 cerning this apparent relationship. The average value, with regard 

 to sign, of the correlations between the yield of sugar beets and other 

 crops is —0.077. 



The correlations between the 9 different cuttings of alfalfa made during 

 1912^0 1914 and all other yields are generally positive and statistically 

 significant in comparison with their probable errors. The only excep- 

 tions are the negative correlation with sugar beets in 191 1 which have 

 already been noted and the slight and statistically insignificant correla- 

 tion for the 1 91 2 yield of alfalfa and the yield of silage corn in 191 8. 



vSince it is quite reasonable to assume that in a crop harvested more 

 than once a year thickness of stand and variation in the size of the indi- 

 vidual plants will have a large influence on the yields of the different 

 plots in the same year, the correlations between the different cuttings 

 of the same year as well as those between single cuttings and totals of 

 two or more cuttings in the same year have been omitted from the tables. 

 The correlations between different cuttings in the same year are given 

 in Table VIII. 



Table VIII. — Comparison of correlations between different cuttings of alfalfa in the 



same year 



We shall now consider the correlations between the yields of alfalfa 

 and between the yields of alfalfa and of other crops on the same plots in 

 different years. The individual constants may be studied in the funda- 

 mental table (Table IV). The averages are given in Table IX. This 

 shows that the correlations between different cuttings of alfalfa are on 

 the average larger throughout than those between the yield of alfalfa 

 and the yields of other crops on the same plots. 



