PHOTOSYNTHESIS 25 



was no carbon dioxide, but which contained sufficient carbon 

 monoxide to give a concentration of this gas in the cell-sap equiva- 

 lent to that in which C02 is normally present, the plants grew 

 normally and apparently elaborated starch; third, other and more 

 extensive experiments indicated, however, that green plants in 

 general cannot make use of carbon monoxide gas for photosyn- 

 thesis, although this does not prove that von Baeyer's idea that 

 CO is a step in the process is necessarily erroneous; and finally 

 it was shown that carbon monoxide, in sufficient concentration 

 to produce the results with Tropaeolum mentioned above, usually 

 acts as a powerful anaesthetic towards most other plants. While 

 these considerations do not positively prove that von Baeyer's 

 hypothesis is incorrect, they render it so improbable that it has 

 generally been abandoned in favor of others which are described 

 below. 



Erlenmeyer, even before the experimental work mentioned 

 in the preceding paragraph had been reported, suggested that in- 

 stead of assuming a separate breaking down of the carbon dioxide 

 and water, it is easier to conceive that they are united in the 

 cell-sap into carbonic acid and that this is reduced by the 

 chlorophyll-containing protoplasm into formic acid and then to 

 formaldehyde, as indicated by the following equations: 



1. H 2 C0 3 = H 2 CO 2 +0 



2. H 2 CO 2 = CH 2 O+O 



Like von Baeyer's hypothesis, this assumes that formaldehyde 

 and oxygen are the first products of photosynthesis. 



Proceeding upon this assumption, many investigators have 

 studied the question as to whether formaldehyde actually is 

 present in green leaves. Several workers have reported successful 

 identification of formaldehyde in the distillate from green leaves; 

 while others have criticized these results and have maintained 

 that formaldehyde can likewise be obtained by distilling decoc- 

 tions of dry hay, etc., in which the photosynthetic process could 

 not possibly be conceived to be at work. Other investigators, 

 notably Bach and Palacci, reported that they had succeeded in 

 artificially producing formaldehyde from water and carbon diox- 

 ide, in the presence of a suitable catalyzer or sensitizer. Euler, 



