368 



A Quantitative Analysis of the Growth of Helianthus annuus. 

 Part I. — The Respiration of the Plant and of its Parts 

 throughout the Life Cycle. 



By Fkanklin Kidd, Cykil West (Research Workers, Food Investigation 

 Board), and G. E. Briggs (Demonstrator in Plant Physiology, Botany 

 School, Cambridge). 



(Communicated by Dr. F. F. Blackman, F,E-S. Eeceived August 9, 1921.) 



CONTENTS. 



PAGE 



1. Introduction 368 



2. The Eespiratory Index as a Measure of the Effect of the " Internal " Factor 



upon the Eate of Kespiration 369 



3. Material and Methods 370 



4. Experiments to Determine the Eelation between Temperature and Eespira- 



tion, and a Suitable Temperature at which to Determine the Eespiratory 



Index 371 



5. The Decrease with Age in the Eespiratory Index of the Plant and of its 



Parts 375- 



6. Eespiration of Uncut Plants in the Field 379 



7. The Eelation of the Eespiratory Index to Eelative Growth Eate 381 



8. Summary 383 



1. Introduction. 



By means of a quantitative analysis of plant growth we attempt to 

 apportion the external and internal influences that determine tlie course of a 

 plant's development. The former can be analysed as various recognised 

 environmental factors, tlie latter at present may be grouped together as the 

 " internal " factor for growth. The general methods formulated for such an 

 analysis have been outlined in a previous paper (8). In the present series 

 of papers, of which this is the first, an account is given of such an analysis of 

 the growth of Helianthus annims. The present paper is mainly confined to 

 an account of the results obtained in an experimental study of the respiration 

 of Helianthus annuiLS throughout its life cycle. As far as the authors are 

 aware such a study of the respiration of a plant throughout its life cycle has 

 not before been carried out. 



The method has been to determine at frequent intervals throughout the 

 life cycle, the respiration at a given constant temperature of a representative 

 plant of a crop. From these results it is possible to estimate the respiration 

 of a mean plant of the crop at the recorded fluctuating temperature of the 

 field and so to obtain a measure of the rate of loss in dry- weight of the plant 



