G. E. BriggS, F. Kidd, and C. West 211 



(2) Correlation of Unit Leaf Rate with environmental factors (hiring 

 the carl// part of the life-cycle 1 . 



The environmental factors for which data are given by Kreusler 

 in the different years are as follows (Table V). 



Table V. 



+ means data for this factor are recorded. 



In calculating the coefficients of correlation with mean temperature 

 and hours of sunshine the procedure was as follows. In the year 1875, 

 since the weekly Unit Leaf Rates of the different varieties show r ed very 

 good agreement, the average for the five was taken as expressing the 

 best value. In each year only the values for the five weeks subsequent 

 to the initial rise were used, as the evidence before us indicates that 

 these are least subject to variations due to sampling error. Thus we 

 have a total of 20 cases from which to ascertain the correlation with 

 mean temperature. Since the hours of sunshine were the only record of 

 light intensity for three of the years, the correlation coefficients for the 

 hours of sunshine for the last three years were worked out giving a total 

 of 15 cases. 



The correlation coefficients are as follows: 



With weekly mean temperature, r = -77. 



With weekly mean temperature (years 1876-8), r = -64. 



With weekly hours of sunshine (years 1876-8), r = -47. 



The partial correlation coefficients for the years 1876-8 are as 



follows: 



With weekly mean temperature, r = # 53. 

 With weekly hours of sunshine, r = -24. 



Thus it is seen that the value of the Unit Leaf Rate is governed more 

 by the weekly mean temperature than by the hours of sunshine during 

 the week. 



1 Since the above was written a paper by Brenchley (3) has appeared in which the 

 writer has investigated the correlation between the rate of growth of garden peas grown in 

 water-cultures and environmental factors. In this paper, however, the rate of growth is 

 expressed per unit dry-weight and not per unit leaf-area as in the above. 



