872 EXTERNAL AND INTERNAL FACTORS CHAP. 26 



The curves that would other\vise reach a saturation value high above fciAo 

 will be crowded into a narrow space immediately below fciAo, and the curves 

 with saturation values below fciAo, will all be depressed. A curve the satu- 

 ration level of which would otherwise be iSfciAo will be reduced by the im- 

 position of the ceiling to a saturation level of ^kiAo/(0 + !)• It follows 

 from this formula that, even if the saturation rate without the limitation 

 were only one tenth of the maximum rate of the postulated monomolec- 

 ular transformation of ACO3, it would nevertheless be reduced by 10% by 

 this "potential bottleneck." 



4. Internal Factors and the "Physiological Concept" of Photosynthesis 



The belief, referred to on page 860, that the rate of photosynthesis 

 must obey a simple and rigid kinetic law has been partly responsible for the 

 conclusion, reached by some plant physiologists, that it does not obey any 

 recognizable kinetic law at all. These physiologists, disillusioned by the 

 over-simplifications in which the preceding generation had indulged, turned 

 their attention to the complex relations between photosynthesis and other 

 phenomena of plant life, such as nutrition, respiration, growth or aging. 

 Factors often referred to as "internal" or "plasmatic" are supposed to be 

 responsible for these relations. Stressing the prime importance of these 

 factors in the regulation of photosynthesis, Kostychev and his pupils 

 minimized or denied the direct influence of the easily regulated "external" 

 factors, such as light intensity, CO2 concentration and temperature. 



Their revolt against the apphcatioa of kinetic laws to photosynthesis and similar 

 processes would perhaps be less violent if these physiologists would have reaUzed that the 

 "law of hmiting factors" is by no means the last word in the physicochemical approach 

 to photosynthesis, that, in fact, the concept of "hmiting factors" is foreign to reaction 

 kinetics. The belief that no other kinetic laws are possible led Chesnokov and Bazyrina 

 (19.30) to argue that since, according to Harder and Lundegardh, the factors "carbon 

 dioxide concentration" and "light intensity" are not "truly limiting" (z. e., that often 

 tne change in either of these factors can affect the rate) the "true" limiting factors must 

 be sought inside the plant. It did not occur to them that photosynthesis may have no 

 "true" limiting factor at all. 



Kostychev, in an article called "A New Concept of Photosynthesis" 

 (1931), suggested that "external" factors affect photosynthesis mainly, if 

 not exclusively, in an indirect way, by stimulating or inhibiting certain 

 unknown ])lasmatic activities. All the conclusions obtained by Blacknian 

 (and others l^efore and after him) on the basis of the "ph\sieochenii(ud" 

 approach were rejected Ijy Kostychev as spurious. A similar point of view 

 was taken by van der Paauw (1932) and by Kostychev's co-workers, 

 Chesnokov and Bazyrhia (1930, 1932), who sought to prove by experiments 

 that two external factors — carbon dioxide concentration and temperature — 

 have no direct effect on the rate of photosynthesis at all, and that the third 



