Chapter 33 



TIME EFFECTS. I. INDUCTION PHENOMENA* 



The preceding chapters dealt with kinetic relationships in the stationary 

 state, even if we have not quite succeeded in eliminating all references to 

 time, for example, when speaking of the effects of high temperature (chapter 

 31), or excessive light (chapter 28), or when discussing the influence of 

 chlorophyll content on oxygen yield in flashing light (chapter 32). The 

 following two chapters deal specifically with two tj^pes of "time effects": 

 the phenomena occurring in the initial period of steady illumination (induc- 

 tion effects), and the consequences of regular alternation of darkness and 

 light (photosynthesis in intermittent light). 



When these chapters were first written a few years ago, one could be 

 relatively optimistic about the possibility of organizing the various findings 

 in the field of induction phenomena under a few simple headings. Induc- 

 tion appeared simply as delayed dart of photosynthesis after a period of 

 darkness, with the extent of the delay depending on the duration of the 

 dark period and the conditions to which the cells had been exposed during 

 this time. 



Investigations of fluorescence changes at the beginning of illumination 

 first revealed, and application of rapidly registering methods of oxygen and 

 carbon dioxide determination subsequently confirmed, that induction is 

 not, or not always, so simple. It may involve a brief initial burst of ac- 

 tivity, followed by one or more waves of inhibition. Furthermore, the 

 time courses of oxygen evolution and of carbon dioxide consumption dur- 

 ing the induction period are not always parallel; instead, the photosynthetic 

 quotient, Qp( = AO2/— ACOo) may vary during this period, deviating far 

 from its normal value of +1.0, and occasionally even changing its sign (for 

 example, carbon dioxide may be liberated simultaneously with oxygen). 



The chapter was rewritten in the light of these new observations, and 

 became, in this process, one of the longest in the whole monograph. 



This, unfortunately, was not the end of the trouble. The controversy 

 over the maximum quantum yield of photosynthesis (see chapters 29 and 

 37D) has caused several observers to study very closely the transient 

 phenomena accompanying the transfer of cells from dark to light, or 

 changes in the intensity of illumination, since the interpretation of these 

 transient effects appeared highly important for many quantum yield cal- 



* Bibliography, page 1429. 



1313 



