THE YIELD OF ORGANIC MATTER 35 



This was first noticed by Kostychev in 1921. During this so-called in- 

 duction period, which, depending on specific conditions, can last for 

 seconds, minutes or even hours, the photosynthetic quotient may be larger 

 or smaller than unity; it may even become negative, that is, plants may 

 consume (or liberate) both oxygen and carbon dioxide at the same time. 

 These phenomena must be ascribed to the restoration of enzymatic 

 systems and the regeneration of intermediate products, which have been 

 destroyed during the dark interval (c/. Vol. II, Chapter 33). 



Considering all known deviations of the photosynthetic quotient from 

 unity, we see no reason to admit the steady photochemical production of 

 compounds other than carbohydrates. However, the value Qp = 1 does 

 not preclude the formation of organic acids or other "underreduced" 

 compounds as intermediates in photosynthesis. Willstatter and StoU 

 quoted the constancy of Qp as an argument against Liebig's theory of 

 photosynthesis, in which plant acids were supposed to accumulate by 

 photosynthesis in summer, and to be slowly transformed into carbo- 

 hydrates in fall. However, this objection does not avail against those 

 modifications of Liebig's theory which assume that the plant acids are 

 only passing intermediates in the transformation of carbon dioxide into 

 carbohydrates. The observed value of Qp proves that no underreduced 

 (or overreduced) intermediate products accumulate during steady photo- 

 synthesis; but as long as these intermediates are consumed at the same 

 rate as they are produced, their presence cannot affect the photosynthetic 

 quotient (except during the induction period). 



2. The Yield of Organic Matter 



The photosynthetic quotient is the most easily measurable quanti- 

 tative characteristic of photosynthesis. However, it is not suflacient to 

 give a complete picture of the chemical reaction. It does not reveal the 

 absolute value of x in eq. (3.3), or that of the ratio x : y. Thus, it does 

 not allow one to identify the product of photosynthesis as a simple sugar 

 {x = y) or as a polymer {y < x, e. g., y = 5/6 x for high polymers of 

 hexoses). Furthermore, the photosynthetic quotient is not a very 

 sensitive criterion of the exclusive production of carbohydrates. A 

 deviation of Qp by 3% from unity — which is well within the limits of 

 error of most experiments — may mean the formation of as much as 12% 

 of protein (Smith, 1943), or 5% of fats. This makes it important to use 

 other and more direct methods for the determination of the chemical 

 nature of the "photosynthate." Interesting information could be pro- 

 vided by the determination of the amount of water assimilated together 

 with a known quantity of carbon dioxide, but this experiment encounters 

 considerable difficulties, because of the abundant presence of water in all 

 cells. The determination of the total increase in organic matter, caused by 



