472 LIGHT AND LIFE 



which ol tlic two transfers occurs. In those cells in which a strong hick of 

 water exists lor the protected clilorophylls, the unprotected receive a surphis 

 metastal)ie triplet excitation from them, while the accessory pigments transfer 

 singlet excitation. As mentioned in the discussion after Dr. Calvin's talk, the 

 metastable state can carry oat only one of the two photochemical steps con- 

 nected with one splitting of water: singlet excitation is needed for the 

 second step. Thus the cooperation l)etween the products of two absorption 

 acts of different wavelengths, i.e., the Emerson effect, is understandable. 



Dr. French: I am sure I have had that same experience, Professor Franck, 

 in having people not pay attention to what I think important. The only 

 thing that I have against this is that it is hard to think of a part of the 

 inside of the chloroplasts as being protected from water, water being such a 



small molecule. 



Dr. Franck: If I speak of protection from water, I mean only protection 

 against water as a fluid. Clertainly, protein contains water, but if for each 

 chlorophyll at the lipid layer one water molecule should be available, its 

 concentration should be high, as high as that of chlorophyll. Furthermore, 

 I expect only small water concentrations at the position where the chloro- 

 phyll is adsorbed; it is itself not water-soluble, and the fatty acid side of the 

 lipid will repel water, too. The proixibility of finding water at the phosphate 

 group is supposed to be much greater. 



Another point I want to mention is that your scheme does not contain 

 any explanation why (according to Duyscn's and your remarks) . the 

 fluorescence intensity of chlorophyll a in red algae is higher if the light 

 is absorbed by phycobilins than if chlorophyll n absorbs it. 



Dr. French: I am sure a lot of things don't fit in that little scheme. I 

 don't take it very seriously except as a means of correlating the facts we have 

 discussed. 



Dr. Rauinowitch: I just wanted to answer Dr. Franck. My manuscript 

 contains a discussion of your interpretation. I didn't have enough time to 

 mention it in my talk, and 1 thought you were going to bring it up anyhow 

 so I did not discuss it. It was just a question of time. The other thing that 

 I would say is that your interpretation suggests something about the 

 fluorescent capacity of the diflerent forms of chlorophyll. 



Dr. Weber: 1 would like to ask Professor Franck how he proposes to 

 reconcile the oI)ser\ed half-life of five seconds of the two effects with 

 metastable states which have a half-life of only a fraction of a second. The 

 two illuminations enhance each other even when one comes five seconds 

 after the other. How is this compatible with metastable states which last 

 only a fraction of a second? 



Dr. Franck: You speak of my older idea of a cooperation Ijelween a 

 metastai)le trii)Iet state and a singlet state, to reach a higher excited state 

 of chlorophyll. This idea, which I called 'physical cooperation," I supple- 

 mented by the picture of a •(hemi(al cooperation,' and finally gave up the 



