PHYSIOLOGICAL STUDIES 



57 



actual consumption of oxygen in photo-oxidation and for 

 this reason Franck (1949) has postulated that under condi- 

 tions of photo-oxidation there is produced in the cell a 

 depressant of photosynthesis. He has assigned a further 

 function to this substance or 'narcotic' which we shall dis- 

 cuss when we refer to work on fluorescence later in this 

 chapter. 



Chlorophyll. The effect of the concentration of chlorophyll 

 upon the rate of photosynthesis of the green plant was 

 investigated by Willstatter and StoU (191 8) whose pioneer 

 work on the chemistry of chlorophyll enabled them to 

 estimate accurately the concentration in different plants. 



TABLE 4.1 



VARIATION IN ASSIMILATION NUMBER IN LEAVES OF DIFFERENT PLANTS 



(from Willstatter and Stoll) 



(Measurements in 5% carbon dioxide, high light and at 25° C. See 

 also the data given in the Appendix) 



Firstly, they showed that as a result of photosynthesis there 

 was no change in the concentration of chlorophyll in the 

 plant. Then they attempted to determine for a number of 

 different plants, the maximal rate of photosynthesis, in mg. 

 carbon dioxide per hour, per mg. chlorophyll in the tissue 

 — a quantity they called the assimilation number. Measure- 

 ments were made with a flowing gas technique with a high 



