4 5 6 7 8 9 hrs. 

 —♦— Fucus serratus— Cloud 

 — • — Fucus serratus — Sunlight 

 — o— Fucus platycarpus —Cloud 

 —O— Fucus platycarpus — Sunlight 



9 hrs. 



12 

 10 



^ 8 



O A 



U 4 



^ 2 



txo *■ 



E 



-2 



-4 



Fucus platycarpi 



Respiration Curves 



Fig. 213 A, water loss, and B, assimilation in relation to exposure 

 (drying) on sunny and cloudy days. C, D, effect of temperature on 

 respiration and assimilation of Fucus. Investigational period for 

 assimilation, 5 min.; for respiration, 18 min. (After Stocker and 



Holdheide.) 



often occur at depths of 40-70 ft. in turbid water but at 90-100 ft. 

 or more in clearer waters. This has been further demonstrated by 

 Tschudy (1934)5 Stocker and Holdheide (i937) and also in New 

 Zealand. In the first-named study, maximum photosynthesis oc- 

 curred at the surface on choppy days but at about 5 m. on calm 



396 



