282 



PHYSIOLOGY, SYMBIOSIS, ETC. 



invalidated in that no allowance was apparently made for any 

 temperature effect. 



Tshudy inserted the algae to be investigated into test tubes 

 which were then placed horizontally in wire baskets that could be 

 lowered to any required depth. The oxygen was measured in these 

 tubes before and after each experiment by the Winkler method. 

 Estimations were also made on blank controls, but as these exhi- 

 bited some fluctuations the conclusions from the experiments 

 themselves ought to be accepted with some degree of caution. 



Tshudy found that: 



(i) At 25 m. depth respiration takes place more rapidly than 

 photosynthesis, but for the species investigated in that particular 

 area there is a sHght balance in favour of photosynthesis at 22-5 m. 



B 



-^<— Iridaea. 

 -« — TurnereUa 

 Voter Contrvl 



J L. 



15 20 22-5 25 



o-sU- — --.^__ ?=^o-^- 



1 3 5 7-5 10 15 2022-525 13 5 7-5 10 



Depth in metres 



Fig. 180. Assimilation of two species of the Rhodophyceae in relation to depth 

 and weather conditions. A, cloudy day and water slightly choppy. B, clear, 

 calm day. (After Tshudy.) 



(2) Photosynthesis is materially affected by the degree of cloudi- 

 ness and the state of the w^ater, w^hether it is calm or choppy. The 

 influence of these tw^o factors can be seen from an examination of 

 fig. 180. 



(3) On clear calm days maximum photosynthesis occurred at a 

 depth of about 5 m., but on choppy days it occurred at or near the 

 surface (fig. 180). 



From the above results it was concluded that the red phycoery- 

 thrin acts largely as a colour screen, the plants utilizing the light in 



