347 



L. R. Blinks 



Figure 1. Apparatus for 

 measuring pH changes due to 

 CO2 exchange in membranous 

 algae. A thallus (th) is held 

 by capillarity against the 

 active glass electrode surface 

 (the remainder being waxed). 

 The tip of the tissue dips 

 into sea vater. KCl-agar salt 

 bridges (sb) connect to 

 calomel electrodes. 



At the beginning of the recent work on algae, a few records 

 were taken with the "fluid" arrangement, in an everted electrode 

 especially with the filamentous green alga Chaetomorpha , and 

 the delicate branched red alga Antithamnion (in normal sea water) . 

 The results with the former are shown in Fig. 2. The pH drifts 

 downward in the dark, then after a slight "acid gush" Increases 

 rapidly in the light. With less intense monochromatic light at 

 702 mi-i, compensation was just reached, at which the pH remained 

 constant. The same was approximately true at 6U5 my, (absorbed 

 by chlorophyll b). If the intensity of either of these was 

 doubled, the rise of pH just about equalled the fall in the dark. 

 On the other hand if the two wave lengths were given together, 

 the rise of pH was about twice as fast as the previous fall in 

 the dark. This gives an enhancement of some 50^ or a factor 

 E of 1.5, where E= a,b (simult.)/ a + b. Just as with oxygen 

 evolution, CO2 fixation shows good enhancement. 



With the second arrangement, (membranous algae) normal air 

 (sat-urated with water vapor) was passed slowly through the jar; 

 in a few cases air enriched with l/o CO2 vas used, but this tended 

 to buffer the tissue too well, and gave smaller pH changes on 

 illumination. The tissues, especially Enteromorpha and Porphyra 

 perforata , tolerated this exposure to moist air very well, and 

 could be used for several days. In the case of Porphyra , some 

 of the intercellular wall materials (comparable to agar) no doubt 



