214 MELVIN CALVIN 



magnetic, bivalent cation such as zinc, then this molecule can have a long-lived 

 triplet state, which is essential for the energy-migration and conversion with any 

 high degree of efficiency. 



I suspect that the rudimentary beginnings of a chlorophyll-t)'pe of photo- 

 synthesis may have occurred in the precellular period, in a period in which one 

 had already seen the appearance of Upid-type coacervates and in which the disc- 

 like molecules of chlorophyll could assume a pseudo-crystalline arrangement, 

 facilitating the energy transport and conversion. In all probabiht>', it was at 

 this point, or very near this point, that the ceUular habit of life took shape. 

 Finally, the generation of the oxygen-evolving mechanism, perhaps requiring 

 the participation of the carotenoids and other such materials, occurred, leading 

 to the higher plants, and to the whole potential of oxidative evolution. 



I 



