NUTRITION 



59 



ing the starch molecule are known, and therefore it is custom- 

 ary to give either the minimum formula or to indicate by 

 n that the starch molecule should be represented by some mul- 

 tiple, probably high, though still undetermined, of the mini- 

 mum proportional formula. The proportional amounts of 

 the end substances are indicated, therefore, by this equation 



n(6 CO, + 5 H 9 0)=n(C 6 H 1 .O fc + 6 O f ) 



Starch, though frequently termed the first visible product of 

 photosynthesis, is not formed in all chlorophyll-containing 

 cells (e.g. those of onion leaves), and should never be re- 

 garded as the first product of photosynthesis. The com- 

 plexity of the starch molecule and the simplicity of the 

 molecules of carbon-dioxide and water, indicated by their 

 respective proportional formulae and still more plainly by 

 their structural formulae, * make it extremely doubtful if even 

 the commoner sugars are formed directly. These, because 

 they are formed and remain in solution, can be recognized 

 only by chemical means, while starch, a solid with a refrac- 

 tive index different from the other substances in the cell, is 



* The structural formula of CO 2 is probably O = C 

 " " " " H 2 O " H O H 



" " n (C. H 10 ) may be 



As examination of this structural formula shows, 

 C fi H 10 O 5 is only an approximate proportional for- 

 mula for starch. It would be more correct to rep- 

 resent starch thus, n ( C 6 H 12 O 6 ) ( n 1 ) H 2 O. 

 Evidently, the higher the multiple represented by n, 

 the nearer this formula will come to the propor- 

 tional C 6 H 10 O 5 . These proportions were obtained 

 by analysis. The exact numbers can be learned only 

 by synthesis, and no one has yet been able to make 

 starch. 



= O 



n 





H 



I 

 H-C-OH 



H C-OH 



H-C-OH 



I 

 H-C-OH 



I 

 H-C-OH 



H C-OH 

 H-C-OH 



H-C-OH 



I 

 H-C-OH 



H C= O 



