Quantitative Analysis of the Growth q/" Helianthus annuus. 383 



temperature. In view of this and of the fact that the correlation coefficient 

 of this ratio with temperature is — 0'34, it would seem either that the relative 

 growth rate (when not limited by such factors as carbohydrate or salt supply) 

 has a lower temperature coefficient than respiration, or that the relative 

 growth rates at higher temperatures are limited by some factor. 



In view of the close relation between the respiratory index and nuclein 

 nitrogen, as established by Palladin (7), on the one hand, and that between 

 tlie respiratory index and the relative growth rate, as demonstrated above, on 

 the other, one would expect the growth rate to be intimately connected with 

 the concentration of nuclein nitrogen per gramme dry-weight. It must be 

 realised, however, that whereas the first relation was established for wheat, 

 the second was established for Relianthus annuus. 



The only type of evidence availalile with regard to the third suggested 

 relation is that provided by the results obtained by Hornberger (3), who 

 determined the protein nitrogen-content of maize. These results are for the 

 same plants as those for which we have already calculated the relative 

 growth rate (1). The growth per protein nitrogen for successive weeks, 

 which we have calculated, is as follows : — 



Grammes dry-weight per gramme Nitrogen per Week. 

 22-0 32-4 

 42-5 20-0 

 25-9 15-2 

 27-7 16-2 

 38-1 27-5 



As to the relation of nuclein nitrogen to protein nitrogen we at present 

 have no evidence. 



It is proposed to reserve further consideration of the relation between 

 respiration and growth until we have presented the growth data in full. 



8. Summary. 



The respiratory index has been defined as the respiration determined per 

 gramme dry-weight per hour at 10° C. when the amount of respirable 

 material is not limiting and when the external concentration of oxygen is 

 that of the atmosphere. The respiratory index is consequently a measure of 

 the effective amount of respiring cell-matter per gramme dry-weight, that is 

 the " internal " factor for respiration. 



The respiratory index of the entire plant falls off continuously from 3 

 to about one-tenth of this value at the end of the life-cycle. The respiratory 

 index of the stem of individual leaves and of the flowers respectively 



