PHOTOSYNTHESIS 23 



It is apparent, however, that the process is not so simple as 

 this hypothetical reaction would indicate, as water and carbon 

 dioxide can hardly be conceived to react together in any such 

 simple way as this. Various theories as to the exact nature of the 

 steps through which the chemical combinations proceed have been 

 advanced. A discussion of the experimental evidence upon which 

 these are based and of the conclusions which seem to be justified 

 from these experimental studies is presented below. The only 

 value which may be attached to the empirical equation just 

 presented is that it does accurately represent the facts that a 

 volume of oxygen, equal to that of the carbon dioxide consumed 

 in the process, is liberated and that formaldehyde is the synthetical 

 product of the reactions involved. 



It should be noted, in this connection, that formaldehyde 

 is a powerful plant poison and that few, if any, plant tissues 

 can withstand the toxic effect of this substance when it is present 

 in any considerable concentration. Hence, it is necessary to this 

 whole conception of the relation of formaldehyde to the photo- 

 synthetic process, to assume that, however rapidly the formalde- 

 hyde may be produced in the cell, it is immediately converted 

 into harmless carbohydrate forms. 



THE CONDENSATION OF FORMALDEHYDE INTO SUGARS 



As has been mentioned, it is easily possible to cause either 

 formaldehyde, or trioxymethylene, to condense into CeH^Oe, 

 using milk of lime as a catalyst. Of course, no such condition 

 as this prevails in the plant cell, and the mechanics of the proto- 

 plasmic process may be altogether different from those of the 

 artificial syntheses. Furthermore, the hexose produced by the 

 artificial condensation of these simpler compounds is, in every 

 case, a non-optically active compound, while all natural sugars 

 are optically active (see Chapter IV). Emil Fischer has suc- 

 ceeded, however, by a long and round-about process which need 

 not be discussed in detail here, in converting the artificial hexose 

 into glucose and fructose, the optically-active sugars which occur 

 naturally in plant tissues. The condensation of formaldehyde 

 directly into glucose and fructose in the plant cell is brought 

 about by some process the nature of which is not yet understood. 

 Probably synthetic enzymes (see Chapter XIV), whose nature 



