406 Quantitative Analysis of Plant Growth 



With regard to the second paragraph of Mr Fisher's summary 

 we do not wish to reopen the discussion on the significance of the 

 "Efficiency Index." Equation (1) given above for calculating relative 

 growth rates is the same as Blackman's formula for calculating the 

 "Efficiency Index (l)." There is nothing original in the formula itself, 

 but whereas we propose an analysis by an evaluation of the Relative 

 Growth Rate for weekly or for shorter periods 1 throughout the life- 

 cycle, Blackman(i) and Brenchley(2) used this formula indiscriminately 

 for periods of widely varying length and covering widely different 

 portions of the life-cycle. 



Botany School, 

 Cambridge. 



REFERENCES. 



(1) Blackman, V. H. The Compound Interest Law and Plant Growth. Ann. Bot. 



xxxm. 353, 1919. 



(2) Brencbxey, W. E. Some Factors in Plant Competition. Ann. Appl. Biol. vi. 



142, 1919. 



(3) On the Relations between Growth and the Environmental Conditions of 



Temperature and Bright Sunshine. Ann. Appl. Biol. vi. 211, 1920. 



(4) Briggs, G. E., Kidd, F., and West, C. A Quantitative Analysis of Plant Growth. 



Ann. Appl. Biol. vrr. 103, 1920. 



(5) West, C, Briggs, G. E., and Kidd, F. Methods and Significant Relations in 



the Quantitative Analysis of Plant Growth. New Phytologist, xix. 200, 1920. 



1 We have used weekly periods as no data for shorter periods are at present available. 

 Daily or half-daily measurements would provide data for a much deeper analysis. 



