438 H. GAFFRON 



looked upon as a normal component of all aerobic induction 'periods. 

 [ believe Fig. 8 provides the answer. 



These algae happen to start actual photosynthesis very quickly 

 when the light is turned on — as, for instance, at the end of line c. In 

 Fig. 8, a, h, c, and d are parts of a continuous recording. They were 

 cut out of the chart and pasted below one another for easier com- 

 parison. If after a dark period the light is not left on for longer than 

 1 or 2 seconds, we obtain an immediate break in the respiration 

 curve — but no photosynthesis. 



Instead respiration remains compensated during the following 20 

 to 40 seconds in the dark (as after T in line h) before it resumes its 

 normal course. It is not difficult to find the right interval when a re- 

 newed flash of fight will prevent the reappearance of respiration and 

 prolong the compensation for another 40-second dark period. Be- 

 ginning with i on fine a this sort of play with properly timed flashes 

 produced a compensation period lasting here 8 minutes. Obviously 

 the size of pools of intermediates and the reaction rates determine the 

 outcome of such an experiment, and it is not too surprising to see how 

 an interposed illumination lasting 40 seconds (between lines h and c) 

 disturbs conditions. Now (fine c) 2 seconds of light not only start a 

 compensation reaction but also some photosynthesis followed by an 

 enhanced respiration long before the 40 seconds of the former com- 

 pensation period are over. By cutting the light as well as the dark 

 period in half — leaving the integrated times unchanged — that is, 

 giving now a 1 -second flash every 20 seconds — restores the original 

 compensation effect. Another minute of strong photosynthesis, be- 

 tween lines c and d, interferes with this arrangement. One second of 

 light produces a compensation period in the dark which ends short of 

 19 seconds. We see that respiration starts each time just before the 

 next flash initiates a new compensation. The last flash in this pic- 

 ture was given at t hne d, and folloAving the dark pause of 18 seconds 

 the carbon dioxide of respiration suddenly appears at a rate which 

 now is three times that at the beginning of the experiment. 



What do these recorded curves for carbon dioxide tell us about the 

 nature of induction periods and aftereffects? The last-described 

 effects make it clear that compensation reactions may occur even if 

 they are not so obviously visible as in Fig. 3, and that they precede 

 those reactions which lead somewhat later to the net uptake of carlwn 

 dioxide. Substances which in the dark usually decompose with the 



