G. E. Briggs, F. Ktdd, and C. West 405 



elaborated this comparison. It was decided to present the majority 

 of the results in that paper in the form adopted (i.e. calculated by- 

 equation (2)) in order that the calculation might be perfectly intelligible 

 to non-mathematical readers. Mr Fisher's attack centres round this 

 point and amounts to a statement that for statistical purposes the 

 results obtained by equation (1) are preferable to those obtained by 

 equation 2. Since we did not attempt any statistical correlations in the 

 paper under consideration his criticism is irrelevant. 



Miss Brenchley, with Mr Fisher's help, has utilised Relative Growth 

 Rates calculated by equation 1 for determining the correlation between 

 growth rate and temperature and sunshine respectively (3). We agree 

 that the values calculated from our first formula (equation 1) are the 

 values to be utilised for statistical correlations provided due considera- 

 tion be given to the complexity of the problem. We propose to consider 

 this question in detail in another place. 



The explanation of Mr Fisher's misunderstanding is most probably 

 to be traced to the discrepancy between our definition of Relative Growth 

 Rate and Mr Fisher's and to the fact that he imputes his definition to us. 

 While w r e define the Relative Grow r th Rate as the weekly percentage 

 rate at which the dry- weight increases, in a previous number of this 

 Journal ((4), p. 104) we pointed out, as Mr Fisher himself quotes, that 

 "the principle of the proposed method of expressing rate of growth is 

 analogous to that of the method by which the rate of most reactions, 

 both chemical and physiological, are expressed, namely, amount of 

 change per unit of material per unit of time." This precise physico- 

 chemical definition, to which we say our definition is only analogous, 

 Mr Fisher adopts as a definition of Relative Growth Rate and imagines 

 we have done likewise, which we have not. Our attitude is that until 

 we gain a more thorough knowledge of the complexity of the processes 

 involved in plant growth, the adoption of a definite physico-chemical 

 conception is not warranted since it may lead to the mistaken impres- 

 sion that its adoption constitutes in itself an advance in physiological 

 knowledge. 



His charges of "inconsequent arbitrariness in method of calculation 

 when contrasted with precision of definition," and his imputation that 

 our choice of method of calculation is explainable by "the mistaken 

 impression that the use of the logarithmic formula involves the assump- 

 tion that the relative rate of increase is independent of time," when 

 viewed in the light of the above discrepancy of definition can be readily 

 explained. 



