727 



William Vidaver 



time course of oxygen evolution during illumination. 



c 

 o 



_2 

 o 

 > 



o 



q: 



_L 



_L 



3 4 5 

 Time.min 



Fig. 1. Induction time course of oxygen evolution in 

 Porphyra perforata . (15° C., 1000 psi.) 



In this study two types of observations of pressure effects 

 were made on the time course of oxygen evolution induction in al- 

 gae. One of these recorded oxygen evolution rates under constant 

 illumination; the other determined pressure influence on oxygen 

 evolved by algae in response to light flashes. 



Four algal species were observed in these experiments. These 

 were selected because they represent some of the wide variety of 

 algal types. A second consideration of selection was that the 

 marine species are extremely thin thalloid forms and consequently 

 present minimal barriers to light transmission and gas diffusion. 

 Porphyra perforata is a marine red alga one cell thick, while the 

 green marine alga Ulva lobata consists of two cell layers. Ilea 

 fascia , a marine brown alga, has a complex parenchymatous thallus, 

 but is quite thin in cross section. The green freshwater uni- 

 cellular alga, Ankistrodesmus f alcatus . was also used. 



METHODS 





Discs of algal thalli were placed in contact with a platinum 

 electrode polarized at -0,6 v., which along with a silver-silver 

 chloride reference electrode, could be enclosed in a pressurized 

 optical cell (described elsewhere)^ ^. Unicellular algae were 

 taken up on a disc of cigarette paper which was then applied to 

 the electrode. For marine algae, seawater was used as both the 

 medium and the hydraulic fluid. Tapwater was substituted for the 



