EVOLUTION BY Chlorella: 11 



425 



suspensions are shown in Fig. 6. Here the superposition of the burst 

 upon the very slight induction delay of the maximum sustained rate 

 by dark periods of 6 to 9 seconds causes a momentary overshoot. 

 Longer dark periods (2 minutes or more) delay the sustained rate 

 sufficiently to partially resolve the burst at lower magnitude, as 

 shown in the previous paper by much longer dark treatment (2 hours). 

 This further distinguishes the burst reaction from CO2 fixation. 



UJ 



20 



18 



z 

 . I 4 



CO 



I 2 



10 



E 6 



z 



- 4 



O 2 



t- 



3 



o 



> -2 



N 



O -4 



1 — r 



• 7.0 m^ MOLES OF O2 /ml. 

 A 2.5 m/i MOLES OF Og / mL 

 O 1.0 m^ MOLES OF O2 / ml. 



-^8P=M 



U L_ 



6 12 18 



TIME IN SECONDS 



J 1 1 1 1 \ 1 1 1 1 \ I I I ■ I ■ 



24 30 36 42 48 54 



60 



Fig. 7. Typical successive O2 bursts occurring at increasing O2 concentrations 

 showing disappearance of the secondary ma.ximum. First O, second A, and 

 third • bursts. 



Attention has been called above (Figs. 1 and 2, etc.) to the short 

 duration of the burst maximum when oxygen limited. Plotting, with 

 extended time scale, successive oxygen burst rates occurring at in- 

 creasing oxygen concentrations shows, detailed in Fig. 7, the resulting 

 progressive change leading to the disappearance of the secondary 

 maximum. By choosing proper conditions of light intensity and time 

 ratio of successive dark and light intervals, the transition stages of this 

 effect may be recorded (Fig. 8) and studied in detail. They are char- 

 acterized by a gradual increase of the secondary maximum leading to 



