72 CHAP. IX. EFFECT OF TRACES OF CHEMICAL SUBSTANCES 



photosynthetic activity. The effect of traces of formal- 

 dehyde in enhancement of activity is of special significance 

 in regard to the possible formation of formaldehyde as the 

 first product of photosynthesis. 



At first sight it seems inconceivable that infinitesimal 

 traces of certain chemical substances should have such a 

 potent influence in the life-activity of plants. There is, 

 however, no doubt of the reality of the phenomenon. 



