ECOLOGICAL FACTORS 



359 



thrin-rich red algae assimilate far better in green light than the 

 green and brown algae, and this is valid for both surface and deep- 

 living species. In blue-green light, on the other hand, the per- 

 formance of the fucoxanthin-rich Phaeophyceae far surpasses that 



GrowtK 

 In. mrrt. 



200 



t 



100 



GrowtK 

 In mm. 



300r 



200- 



100 



SCYTOSIPHON 

 LOMENTARIUS 



t 



100- 



ECTOCARPUS 



CON FERVO IDES 



20 



10 



FUCUS 

 VE5ICUL0SUS 



J_ 



J L 



LTL 



2 4 



8 



10 



Fig. 205. Rate of growth of various algae at different depths in sea water, New 

 Brunswick. (After Klugh.) 



of the Rhodophyceae. It has also been found that the algae of all 

 three groups can be divided into those which are shade algae and 

 those which are sun algae, each possessing a structure that permits 

 of maximum assimilation under the respective conditions. 



Table XXIII 



Shade algae 



Cladophora rupestris, Chlorophyceae 

 Dictyota dichotoma, Phaeophyceae 

 Rhodynienia palmata, Rhodophyceae 



Sun algae 



Ulva lactuca, Chaetomorpha linum 

 Fucus serratus, Pelvetia canaliculata 

 Ceramiuyn rubrum, Porphyra laciniata 



Ehrke (193 1), however, divided the algae into sun and shade 

 groups on the basis of their compensation points, i.e. the light value 

 at which respiration and assimilation are equal. On this criterion 

 the Chlorophyceae and Phaeophyceae form one group, the sun 

 algae, and the Rhodophyceae behave as shade algae. It is evident 

 that the division into sun and shade algae is of considerable 

 significance, but the basis upon which the division ought to be 

 made would appear to necessitate further experimental work. For 



