THE PHOTOTROPHIC ASSIMILATION OF CARBON 45 



fatty acids, like all naturally occurring fatty acids, contain 

 even numbers of carbon atoms (see Table 7) thus giving 

 evidence of their origin from Cg fragments. Again there is 

 the problem of w^hether the reductions required in this 

 synthesis are photochemical or only indirectly dependent 

 on photosynthesis. 



100 



5 



10 

 MINUTES 



IS 



20 



FIG. II. Distribution of radioactive carbon in Scenedesnius obliquus 

 after varying periods of photosynthesis in the presence of 

 carbon dioxide labelled with radioactive carbon. A, lipide 

 and pigment fraction ; B, water-soluble fraction ; C, residue, 

 water-insoluble fraction (after ref. 114). 



Demonstration of the existence of common intermediates 

 in photosynthesis and other metabolic processes leads to the 

 enquiry as to how these systems interact under the dynamic 

 conditions of the living organism. Much of the chapters to 

 follow are concerned with this problem but certain aspects 

 may best be considered at this point. The nature of the 

 interaction of photosynthesis and respiration deserves par- 



