BY JAMES M. PETRIE. 805 



(a) Carbon- assimilation. — Since the hypothesis was first 

 suggested by Baeyer in 1870(4) that formaldehyde is the primary 

 product of photosynthesis, much experimental work has been 

 clone,(5) most of which tends to uphold this view, though it has 

 never yet been completely proved. The most recent view as to 

 its formation is that, through the influence of light and chloro- 

 phyll, water is decomposed, the oxygen being evolved while the 

 hydrogen unites to the chlorophyll. The latter then acts as a 

 strong reducer on the carbonic acid in solution in the cell-sap, 

 whereby it is reduced to formic acid, then to formaldehyde. 



H 2 C0 3 carbonic acid ... (COOHOH) 



H 2 C0 2 formic acid (CO'OH-H) 



H 2 CO formic aldehyde (CO-H-H) 



This aldehyde is the probable starting point for the higher 

 synthesis wherein the various groups CH 2 , CHOH, COOH, 

 become linked together into long chains forming the carbohydrates 

 and fats. In the first stage of the mechanism of this change the 

 formaldehyde has ever proved elusive and difficult of detection 

 in the living plant. The only important facts on which we have 

 to depend are those established by Curtius, Reinke,(6) and later 

 by Pollacci,(7) who have certainly proved that formaldehyde 

 occurs in green leaves growing in light and air. The fact that 

 chemists were for a long time unable to reduce carbonic acid to 

 formaldehyde in vitro was used as an argument against Baeyer's 

 hypothesis, but now this has been accomplished by Fenton,(8) who 

 used magnesium as a reducing agent, at the ordinary temperature. 

 The formaldehyde radicle exists in combination with phosphoric 

 acid as " phytin," discovered independently by Winterstein and 

 Posternack. The latter author states that phytin is formed from 

 the inorganic phosphates during the actual process of the reduc- 

 tion of carbonic acid b}* - chlorophyll. 



The second stage, the synthesis of sugars and their conversion 

 into starch and fat, is more easy to comprehend, since it is 

 possible to perform these apart from the living cell, as for 

 example, the aldol condensation from formaldehyde to glucose. 

 Then it is possible to conceive the hydrolysis of starch into sugar 



