TISSUES FOR SYNTHESIS 133 



controversy over the exact chemical reactions involved, 

 and the two sets of reactions given represent possi- 

 bilities rather than actualities. 



= HOOOH+H 2 2 ; 



formic acid 



6(CH 2 0)=C 6 Hi 2 6 ; 



glucose 



(C 6 H 12 6 ), = (CeHioOs)* + (H 2 O),. 



starch 



2. 6C0 2 +5H 2 O = C 6 H 10 5 +60 2 . 



In the first set of reactions formic acid is formed 

 from carbon dioxide and water. An unknown number 

 of molecules of this acid is transformed into a substance 

 having the formula of a typical carbohydrate (CH 2 0). 

 This carbohydrate substance, by rearrangement of 

 the elements composing it, is transformed into glu- 

 cose. The glucose is converted into starch by the 

 elimination of a molecule of water. The second 

 reaction assumes a direct formation of starch from 

 the carbon dioxide and water with the liberation of 

 oxygen. The weight of opinion inclines toward the 

 building up of a series of intermediate compounds 

 as indicated in the first reaction. Chloroplasts and 

 light are essentials in both reactions. 



Although the exact nature of the chemical changes 

 occurring in the construction of starch substance 

 are in doubt, the manner in which the starch granule 

 is built up by the chloroplast is fairly well under- 

 stood. The chloroplasts are protoplasmic cell con- 



