1316 INDUCTION PHENOMENA CHAP. 33 



tion is complete without determination of both the carbon dioxide and the 

 oxygen exchange — a icHiuirement satisfied by very few of the available 



studies. 



In addition to induction losses, induction gains, in the form of "bursts'' 

 or "gushes" of oxygen, or "gulps" of carbon dioxide, also have been ob- 

 served, sometimes simultaneously, and sometimes independently of each 

 other. We can speak in such cases of inverse or positive induction, in con- 

 trast to normal or negative ones. Here, again, the maximum volume of the 

 bursts or gulps is restricted by the maximum amount of "carrier" or "ac- 

 ceptor" molecules that can accumulate in the cell in darkness. 



The determination of the induction losses or gains is dependent, as 

 are all measurements of photosynthesis, on the assumptions made concern- 

 ing the course of respiration during the light period. Here, too, the picture 

 is becoming more, rather than less, confused as a result of recent studies. 

 The exchange of both oxygen and carbon dioxide, which has become con- 

 stant (or only slowly changing) after a long dark period, undergoes consid- 

 erable fluctuations after an illumination period, reminiscent of the induc- 

 tion phenomena in light, but in general more prolonged; in fact, it may 

 take the respiration a half hour, or even longer, to settle again to a steady 

 rate after a hght period of the order of ten minutes. 



Altogether, it seems that the chemical systems of respiration and photo- 

 synthesis are connected by channels, perhaps on several different levels of 

 reduction, and that several chemical reservoirs in both systems are open 

 to the atmosphere, i. e., capable of exchanging oxygen or carbon dioxide 

 with the medium (through the mediation of appropriate enzymes). While 

 photosynthesis is suspended, all connecting reservoirs are filled to certain 

 levels, depending on the intensity of the oxidative metabolism in the cell. 

 When photosynthesis begins (or its rate changes suddenly), many reservoirs 

 are forced to change their levels, by taking up or absorbing oxygen or car- 

 bon dioxide from the medium, until a new stationary state is reached. In 

 addition to this readjustment of the stores of various respiratory and photo- 

 synthetic intermediates, induction effects may be further complicated by 

 the deactivation, in the dark, of some enzymes needed for photosynthesis, 

 and their gradual reactivation in light ; this may cause some reservoirs to 

 be filled, at the beginning of illumination, above their final steady level; 

 delayed inhibition waves can be caused by such temporary roadblocks. 



If, during the dark period, the plants are deprived of oxygen, they fer- 

 ment (plants left in enclosed spaces can create anaerobic conditions by their 

 own respiration). After a period of such fermentation the induction 

 phenomena are changed. As shown by Gaffron (1935, 1937, 1939, 1940) 

 they can involve, in certain algae, the absorption or liberation of hydrogen 

 {of. chapter 6, and section A7 of this chapter). In other organisms, where 



