In succeeding years much work has been done to check 

 the validity of the cycle, to investigate details of its mecha- 

 nism, and to establish its quantitative importance. 



From almost the beginning of these studies we have been 

 interested in reactions leading from the cycle to various other 

 synthetic intermediates and end products, such as amino acids, 

 sucrose and polysaccharides, and carboxylic acids. As a result 

 of this work we have found that the photosynthetic machine, 

 the chloroplast, is an even more complex and diversified ap- 

 paratus than had been suspected. Not only does it manufac- 

 ture sugars and other carbohydrates, but apparently nearly all 

 other organic materials necessary for its continued growth as 

 well. 



In this book we review the evidence leading to the formu- 

 lation of the carbon reduction cycle and discuss its quantita- 

 tive importance. We describe as far as possible the biosynthetic 

 pathways which we believe exist in the chloroplast. We show 

 how newly reduced carbon from the carbon reduction cycle 

 provides the starting material for these pathways. Our ob- 

 jective is to map complete synthetic sequences from carbon 

 dioxide to final products. Three papers, of fundamental im- 

 portance in the development of the theory regarding the path 

 of carbon in photosynthesis, are included as reprints. 



We are now just at the threshold of discovery of many of 

 the biosynthetic pathways. There is good experimental evi- 

 dence for some and a few clues for others, but for many we 

 must speculate, relying on known, but nonphotosynthetic, 

 pathways. We have called on our experience of some fifteen 

 years' study of carbon fixation patterns during photosynthesis 

 to provide us with clues. The clues help us to predict which 

 reactions, which pathways, and which intermediates may be 

 considered to be likely participants in the photosynthesis of 

 carbon compounds. 



This year Professor Calvin was awarded the Nobel Prize 

 for his work on the assimilation of carbon dioxide during 

 photosynthesis. Those who have worked with him and have 

 experienced the stimulation provided by his enthusiasm and 



vni 



