Gr. E. Briggs, F. Kidd, and C. West 



105 



matical accuracy the increase should be measured over an infinitely 

 short period. This procedure is manifestly impossible, and as we have 

 no exact knowledge of the way in which the relative rate of growth 

 varies over a given period we have adopted the following purely con- 

 ventional method of defining relative rate of growth. The relative rate 

 of growth of a plant during any given week in its life-cycle is the amount 



Relative growth-rate curves for " Badischer Friih " Maize, 1876 



240 



200 



.a 160 



120 



80 



40 



20 2 4 6 8 10 12 14 16 



Week from sowing 



Fig. 1. 



of dry matter which 100 g. of dry matter taken at the beginning of the 

 week adds during the week. A week has been chosen since this is the 

 usual interval between determinations of dry-weight in most experi- 

 ments on growth in plants 1 . It must be realised that the method does 

 not pretend to mathematical accuracy being merely an approximate 

 average for the week, but with such results as are at present available 

 nothing more accurate can be obtained. Even if measurements over 



1 When results are not given for a week we have calculated the increase per 100 g. 



for the period and divided the result by the number of weeks in the period: for example, 



if the period is 8 days and 40 g. increases by 20 g. during that period, then the relative 



. 20 x 100 8 

 rate ,8-^—--. 



