c 



O 



09 



G 



a 



30 25 20 15 10 

 Temperature 



5°C 



Fig. 219 Diagram of paper model to show the combined effects of 

 light and temperature on the rate of apparent assimilation of Fucus 



serratus. (After Hyde.) 



Table 19 



Percentage of normal assimilation re-attained on flooding 



after exposure 



Level 

 High littoral 



Top of 

 mid-littoral 



Middle 

 mid-littoral 



Lower 

 mid-littoral 

 Sub-Uttoral 

 fringe 



Species 

 Pelvetia 

 canaliculata 



Fucus 

 spiralis 



Fucus 



vesiculosus 



Fucus 



serratus 

 Laminaria 



digitata 



70-80% 8-9 hr. after 

 flooding : exposed 1 1 

 days previously 

 49% 8-9 hr. after 

 flooding : exposed 3 

 days previously 

 20% 8-9 hr. after 

 flooding : exposed 3 

 days previously 



Cannot tolerate 3 

 days exposure 



97% 



4 hr. after 



flooding : 



72% exposed 5 hr. 



previously 



in air 90% 



42% R.H. 



Cannot tolerate 

 2 hr. exposure 



There would seem little doubt that illumination and its effect on 

 photosynthesis is an important causal factor, and probably is 

 largely responsible for determining the lower limits of a number of 



403 



