Quantitative Analysis of the Growth 0/ Helianthus aniiims. 381 



7. Tlhc lidation of the Respiratorij Index to Relative Growth Rnte. 



The relative growth rate, whicli we have elsewhere (8)* termed K., is the 

 average rate of increase in dry-weigiit per unit dry- weight per week (expressed 

 as a percentage). In previous papers (1 and 4) we have shown that the 

 relative growth rate appears to vary with age in a manner slightly different 

 for different plants, hut to be always characterised by a fall beginning at an 

 early period in the life cycle ; this fall is very similar to the fall which we 

 have recorded above in the values of the respiratory index of Helianthus 

 anmius. In the present research we can make a direct comparison between 

 the respiratory index, whicli is the rate of respiration per unit dry-weight, and 

 R., since we have the results for the relative growth rates of the same crop of 

 plants as that used for determining the respiration. The comparison is 

 represented in fig. 3 and Table VIII. Fig. 3 shows three curves : — The 



relative growth rate values, the values for the respiratory index and the 

 values for the respiratory activity at the average temperature obtaining in the 

 field, that is, tlie respiratory index corrected to the average temperature in 

 the field by means of the temperature-respiration relationship established 

 above, plotted in each case against days from germination. Table VIII also 

 gives the ratios of relative growth rate to the respiratory index and to the 

 respiratory activity at the average temperature obtaining in the field. 



* = loge W2 - loge Wj, where and Wj are the dry-\veights at tlie end and 

 beginning of the week respectively, and e the base of the natural logarithms. 



2 F 3 



