THE DETERMINING FACTORS IN PHOTOSYNTHESIS 31 



actions are most intense here. The human eye is most sensitive 

 to light in the region of line D ; while photographic plates, because 

 of the silver salts they hold, are most sensitive to the rays between 



G and H. 



In 1864, Sachs found that plants placed under double-walled 

 glass jars with a colored liquid between the two walls, made more 

 starch under a red solution than under a blue one, which shows 



800 



600 



400 - 



200 





ABC D E 



Fig. 3. — Graph showing relative rates of carbon dioxide decomposition in 

 various parts of the spectrum. (After Timiriazef.) 



that the red rays are more important in photosynthesis than the 

 so-called " chemical" rays of the blue end. 



Sachs, however, had not localized the action more closely 

 than the red end of the spectrum. More exact experiments were 

 carried out by Timiriazef (1875) who placed bamboo leaves in 

 closed glass tubes with air containing 5% of carbon dioxide. These 

 tubes were then placed in various parts of the spectrum, and 

 at the conclusion of the experiment the gas was carefully an- 

 alyzed. Fig. 3 shows his results. The greatest decomposition 



