11. THE INTERNAL FACTOR IN PHOTOSYNTHESIS. 

 INTRODUCTORY DISCUSSION. 



It has been realized for some time that in the photosynthetic 

 process taking place in chlorophyllous leaves there is an essential 

 internal factor the nature of which has thus far not been discovered. 

 That such a factor exists is concluded not only from the failure of all 

 attempts which have been made to reproduce photosynthesis outside 

 of the living cell, but recently also from direct experiments with living 

 leaves. The existence of such a factor is especially noticeable under 

 circumstances where the rate of the photosynthetic activity varies 

 quite independently of external conditions. The nature of this 

 factor and the seat of its activity have been given a large variety 

 of purely hypothetical explanations. 



In the course of investigations on certain phases of the problem 

 of photosynthesis which have been in progress for a number of years, 

 it was recognized that a better understanding of the internal factors 

 affecting respiration was a prerequisite to a rational interpretation 

 of photosynthesis. Considerable information on the nature of car- 

 bohydrate consumption in leaves has been gained and has aided 

 materially in the experimental work on photosynthesis. It now 

 seems highly probable that a solution of the problem of the internal 

 factor in photosynthesis can be found in the intimate interrelation 

 between photosynthesis and respiration. 



Pantaneli^ maintained that in photosynthesis the major role is 

 to be ascribed to the protoplasmic function of the colorless com- 

 ponents of the chloroplasts. Willstaetter and Stoll,^ in their splendid 

 and thorough investigation of the relation of the chlorojihyll com- 

 ponents to photosynthesis, attempt to determine whether the 

 differences in the photosynthetic activity of a leaf can be explained 

 by ascribing a dual function to a single chemical component of the 

 chlorophyll. That this factor is not to be sought in the chlorophyll 

 components or in such physical conditions as the degree of dispersion 

 of the chlorophyll pigments follows from the great and irregular 

 disproportionality which has been found to exist between the chloro- 

 phyll-content and photosynthetic activity. Willstaetter and Stoll 

 are of the opinion that besides the chlorophyll there is another 

 chemical agent essential to the photosynthetic. process. The func- 

 tion of this agent they believe can be ascribed either to the general 

 behavior of the plant protoplasm or, in attempting to enter more 

 deeply into its chemical nature, it must be ascribed to a definite 



• Pantaneli, E. Jahrh. f. wiss. BoL, 39, 165 (1903). 



= Willstaetter, R., and A. Stoll. Untersuchungen uebor die Assimilation der Kohlensaeure, 

 41-166 (1919). 

 76 



