1324 INDUCTION PHENOMENA CHAP. 33 



expected — strongly dependent on temperature; its temperature coef- 

 ficient appeared to be about 2. 



Steemann-Nielsen found, with Fucus vesiculosus, at 2.9° C, that the 

 duration of the recovery period (~30 minutes) was not affected by absence 

 of carbon dioxide during the first 10 minutes of illumination. If, however, 

 the plants were deprived of carbon dioxide for as long as 40 minutes in 

 light, the rate of oxygen production immediately after the readmission 

 of carbon dioxide corresponded only to the level usually reached in 10 

 minutes after the beginning of illumination. Steemann-Nielsen saw in 

 this an indication that Fucus contains an internal reserve of carbon di- 

 oxide, sufficient to maintain the normal course of activation for about 10 

 minutes. 



These observations contrast with McAlister's report (c/. section 3) that 

 "activation" of wheat in light can be completed in the absence of carbon di- 

 oxide, so that the carbon dioxide uptake begins at full rate instantaneously 

 after readmission of this gas. (Of course, carbon dioxide uptake by re- 

 plenishment of an empty "reservoir" of bicarbonate in the cells is not im- 

 mediately distinguishable from uptake by reduction, and could occur 

 without the liberation of an equivalent volume of oxygen.) 



It is known (cf. Vol. I, chapter 19) that illumination of plants in absence of carbon 

 dioxide causes photoxidation. The induction phenomena observed after a period of car- 

 bon dioxide starvation must therefore be related to induction phenomena that occur 

 after photoxidation (to be described in section 6). 



It will be noted that none of the experiments discussed so far has indi- 

 cated the occurrence of a "second depression" of oxygen liberation, match- 

 ing a depression often found in carbon dioxide uptake curves (cf. sect. 3), 

 and the "second wave" of fluorescence (cf. part B). Franck, French 

 and Puck (1941) therefore proposed an explanation of the second depression 

 not requiring a parallelism between oxygen liberation and carbon dioxide 

 absorption. Later, however, Franck, Pringsheim and Lad (1945) noted 

 that a second depression actually did occur in the oxygen induction ciu'ves 

 of ChloreUa, as determined by the trypoflavine phosphorescence-quenching 

 method (cf. chapter 25, p. 851). This method can be used only under ana- 

 erobic conditions; but Franck and co-workers considered these conditions 

 irrelevant in this case and concluded that the experiments indicate a second 

 depression of oxygen liberation occurring under the same conditions as the 

 depression of carbon dioxide uptake. 



Warburg and co-workers used the two-vessel manometric technique to 

 calculate oxygen and carbon dioxide exchange, in light and darkness, in 

 minute-to-minute intervals (for a description of the method, cf. chapter 

 25, p. 848; cf. also discussions in chapter 29, pp. 1109-1112, and chapter 

 37D, section 4). 



