DISCUSSION 389 



Ijioclicmital rcsulis gaiiitd wiili tlic mciliod of radioactive tagging. I have 

 the higliest regard for Dr. Oalvin's ehuidalion of the patluvay of carbon in 

 photosynthcsi.s, l)ut physical evidence seems to nic not in accordance with 

 this IiNpoihtsis that hght is nsetl in photosynthesis only lor photoionization. 

 Even tlie problem of ilie (piantuni yield of photoioni/ation is by no means 

 solved. 



Dr. C;-\i.vin: .Ma\ I answer Professor Franck? The cpianiuin yield on this 

 for carrier production is one. 



Dr. Franck: How do you know? 



Dr. Calvin: I measured it. 



Dr. Franck: How? 



Dr. Calvin: By electron spin and by conductivity, both. The two things 

 together. 



Dr. Franck: In the photosynthetic apparatus of the chloroplasts? 



Dr. Calvin: No. I am not talking about chloroplasts. 1 am talking about 

 this system. 



Dr. Franck: Well, I must say this is a much better system than the less 

 ordered chlorophyll layers of the chloroplasts. How great in the chloroplasts 

 is the ratio of the concentrations of quinone and chlorophylls? 



Dr. Calvin: Dr. Franck, may I paraphrase yoiu" remarks? Dr. Franck 

 doesn't believe at the moment there is enough quinone, that is, enough 

 electronic acceptor present in the chloroplast. I don't know the exact num- 

 ber. Do you, Dr. Bishop? 



Dr. Bishop: Yes, approximately 12% of the chlorophyll on a molar basis, 

 and that's a minimum. 



Dr. Franck: That's disagreeable. 



Dr. Calvin: That's a disagreeable minimum? 



Dr. Franck: Yes. 



Dr. Calvin: No, that's quite all right as far as I am concerned. You don t 

 need very many, you know. There will be one quinone for a number of 

 chlorophylls. Some of these chlorophylls, as you yourself have said, are not 

 in active position. 



Dr. Franck: But if certain chlorophyll molecules are not in contact with 

 quinone, how w^ill the quantum absorbed by them be used? 



Dr. Calvin: Resonance transfer to the place where they are. 



Dr. Franck: .Ah. resonance transfer. Once you accept it, I see no need to 

 introduce the concept of electron transfer in photosynthesis. 



Dr. Calvin: That is precisely what we do need. Eventually there must be 

 an electron transfer to the quinones to produce a reducing agent. I believe 

 that a charge migration with little or no temperature coefficient is the best 

 way to separate the high-energy products of the quantum conversion and 

 reduce non-productive back reaction to a minimum. 



I sincerely regret that Dr. Franck has had to offer his criticism of this 

 proposal without having had the opportunity to hear it presented with the 

 evidence. Fortunately the manuscript, which presumably will appear in 



