EVOLUTION BY Chlorella: I 



415 



{6) turiivS on aud off the recorders so that they respond only to the 

 steady value attained in each cycle. 



A slope recorder must, of course, be calibrated. For this purpose a 

 stepping switch produces a known pattern of potential as shown in 

 the first portion of Fig. 3 by the first recorder. The corresponding 

 slope record from the second recorder is shown in the second part of 

 Fig. 3. 



METHODS 



Chlorella cultures were growii aseptically as in (3) t)u1 in "lollipop" vessels 

 provided with more homogeneous bilateral illumination. Cell ronrentrations in 



18 

 16 — 



14 



z 



2 12 



z 



e 4 



z 

 ~ 2 



-It. 



H 



^-4 



'^ 



h 



-6- 

 -8- 



-10 



w 



I^^V*. 



!,-' 



.^ 



[•wM I 



"Nl/fl 



\f^ 



- 



I I I I I I I I — L 



J_J l__L 



TIME IN MINUTE INTERVALS 

 Fig. 4. Portion of original rate record using maximum gain with low CO2 sharply- 

 limiting the sustained rate of O2 evolution. 



all cases were 2^1. cells/ml. (0.2%). Illumination of the polarographic cuvette was 

 accomphshed by a D. C. operated General Electric AH-6 mercury arc through a 

 double Littrow monochromator set at 5780 A. The incident radiant power was in 

 the range of 500 to 600 microwatts and hence far below the saturating level. 



Comparison of our present records with those of our earlier photo- 

 graphic method (3) reveals little new under noi-mal conditions. How- 



