14 OPENING ADDRESS 



efficiency in energy utilization, the quantum number remained about 

 nine, and constant. If purple bacteria and adapted algae use only one 

 half of the mechanism shown in Fig. 3 which is required for full 

 photosynthesis— i.e., for the complete photolysis of water— then there 

 is no obvious spot for the noncyclic phosphorylation which everybody 

 likes now to place at the junction of the two-pigment systems. The 

 bacteria are forced to put extra energy into cyclic phosphorylation. 

 This too might explain an equal quantum number per carbon dioxide 

 reduced. 



If we accept at all the idea that green plant photosynthesis evolved 

 from the simpler system still to be found in purple bacteria, it is not 

 so unreasonable to believe that the twin-pigment arrangement is al- 

 ready present in the latter. Only the differences in potential between 

 the left and right halves of the tandem arrangement did not yet shift 

 far enough apart to allow for a spontaneous dismutation of [OH] into 

 free oxygen with the aid of newly added enzymes such as the 

 manganese- containing one I mentioned earlier. Complicated as this 

 all sounds, I need not remind you that in reality it will eventually turn 

 out to be more intricate still. There are the various sets of accessory 

 pigments, for instance, which seem to be attached either to the bright 

 red or to the dark red absorbing chlorophyll. Why under these circum- 

 stances van Niel's simple concept of an intermediary photolysis of 

 water should have aroused so much opposition, I cannot see. If a 

 theory explains a series of rather diverse observations in a consistent 

 manner, and makes sense from the point of view of increased metabolic 

 potentialities, I prefer it to a disjointed set of explanations of which 

 each one does not reach further than a narrowly circumscribed set of 

 experimental conditions. I am quite confident that despite the great 

 number of new phenomena we are going to discuss during the coming 

 session, there will not be one observation which clearly demands that 

 we abandon van Niel's hypothesis of 1935. In other words, at the end 

 of this week it will be just as much alive as during the years gone by. 



