58 PLANT PHYSIOLOGY 



made from formic acid or formaldehyde regardless of the C02:0 2 

 ratio in these equations. The fact that the ratio happens in 

 nature to be 1 proves only that carbohydrates are the chief 

 end products and not that formaldehyde is an intermediary 

 step. That an enzymatic factor occurs somewhere in the process 

 is indicated also by the work of Molisch (1925), who showed 

 that leaves killed by drying or freezing retain somewhat their 

 power of photosynthesis, while leaves killed by boiling or ether 

 do not. 



4. The formaldehyde is polymerized to sugar. 



The third step in this scheme is sometimes known as the " Black- 

 man reaction," because according to Blackman this is the step 

 which, under ordinary light conditions, controls the rate of photo- 

 synthesis. Thus Warburg has found that KCN affects this stage 

 of the process, but Emerson and Arnold (1932) have produced 

 evidence that this reaction is not affected by narcotics. They also 

 have concluded that the light reaction takes place in about 

 1/100,000 of a second, while the dark (Blackman) reaction requires 

 0.04 sec. at 25° C. and about 0.4 sec. at 1.1° C. It is thus easy to 

 see that various limiting factors may limit different stages in the 

 process. Carbon dioxide may seriously limit the first stage, light 

 the second, and temperature the third. 



Baly's Work. — Baly found that when a solution of formalde- 

 hyde was placed in a quartz tube and exposed to rays of high 

 frequency, at the end of the experiment about 34% of the ma- 

 terial had combined to form sugars of various sorts (10% glucose 

 and about 10% phloroglucin and inosite) and various impurities 

 (14%). He believes that the active formaldehyde forms a ring 

 compound when it first condenses: 



HOH 



C 



/\ 



HOH— C C— HOH 

 HOH— C C— HOH 



v 



C 



HOH 



and that from this ring four things may happen; 



