Chapter 38 

 EPILOGUE 



When this monograph was begun in 1938, .students could still read, in 

 most textbooks of plant physiology, that von Baeyer's formaldehyde 

 theory of 1870 — either in its original form, or as elaborated by Willstiitter 

 and Stoll in 1918 (c/. p. 287) — provided the most plausible picture of the 

 chemical mechanism of carbon dioxide reduction in photosynthesis. 

 The — still older — plant acid theory of Liebig {cf. p. 51), which we now 

 recognize as being much closer to truth, has been completely displaced by 

 von Baeyer's theory, even though no convincing support of the latter, 

 through identification of its suggested intermediates, could be obtained 

 during the many years of its sway. 



The formaldehyde theory made photosynthesis appear as something 

 quite different from, and unconnected to, all the other biochemical activities 

 of the organism. Because of the failure of the attempts to separate photo- 

 synthesis from the living cell, or to divide it into individual steps which 

 could be reproduced in cell-free preparations, it seemed that there must 

 exist one central "secret of photosynthesis," a simple photochemical 

 transformation, whose elucidation will suddenly make us "understand" 

 photosynthesis, and, very likely, will permit us to repeat it outside the 

 living cell. 



Looking back on the change which has come upon the field in the last 

 ten or fifteen years, it seems that it consists, above all, in the abandonment 

 of the idea of a single and simple "solution" of the photosynthesis problem. 

 We have come to realize that photosynthesis is a complex sequence of 

 photochemical and enzymatic reactions. If, for the sake of convenience, 

 we still speak occasionally of the "Blackman reaction" as the non-photo- 

 chemical component of this setiuence, it is generally understood that this 

 term covers a number of consecutive and parallel, forward, backward and 

 side reactions, set into motion, accelerated, or retarded, by the action of 

 light. 



As a sur\ival from the period when photosynthesis appeared a mys- 

 terious, but perhaps uniquely simple reaction, one or the other discovery 

 is still being occasionally hailed as the "final solution" of the problem of 

 photosynthesis. However, the complete mechanism of photosynthesis 

 cannot be revealed by a single new finding — however significant — any 



1979 



