315 



Jack Myers 



CONCLUDING REMAINS 



This discussion has not attempted to consider and explain all 

 observations on enhancement and related phenomena. It has omitted 

 consideration of a q.uite different model which can account for 

 enhancement and respiratory effects of light in Po2-phyridium. 

 The discussion has been based upon an intensive study of two al- 

 gae, Anacystis and Chlorella. With both algae we experienced 

 early difficulties under which we failed to see enhancement at all 

 or obtained inconsistent results. Once these difficulties were 

 recognized and solved we never thereafter failed to see a consist- 

 ent behavior of enhancement. We plan to extend the same rationale 

 to algae of other phyla. 



Finally, comment should be made on possible limitations which 

 accompany the very great advantage of a comparative approach. 

 Availability of algal phyla with different pigment complonents has 

 made it possible to reach the generalization that there are two 

 photoreactions in some way associated with two pigment systems. 

 For example, if we had only data on Chlorella we would still be 

 concerned whether enhancement was in some way peculiar to long 

 wavelength. However, the algal phyla also differ in cell organi- 

 zation. It seems doubtful a priori that characteristics of photo- 

 synthesis will differ between the phyla only in spectral absorp- 

 tion of their pigments. Ability of the green plant to use effi- 

 ciently a broad portion of the solar spectrum seems even more re- 

 markable in the face of the problem of running two photoreactions 

 at some fixed ratio. One cannot avoid the question why, of the 

 several pigment systems developed in the course of evolution, the 

 chlorophyll a- chlorophyll b system became a preferred choice. 



Acknowledgment : This work was supported in part by grant 

 G14365 from the National Science Foundation and grant GM11300-01 

 from the National Institutes of Health. 



