278 PHOTOSYNTHESIS 



3,4-glucosendiol, is in Nef's opinion probably not formed, for it could re- 

 arrange to a mixture of all the theoretically possible aldo, 2-keto and 3-keto 

 hexoses, which is definitely proved not to be the case. On the other hand, 

 to the writer the formation of the 3,4-endiols (both of the glucose and 

 galactose series) is not entirely excluded owing to the fact that in all ex- 

 periments with hexoses a considerable amount of tar is formed. This 

 may arise from a splitting of the 3,4-endiols into two molecules of 

 glycerine aldehyde which may polymerize to a tar. The writer has 

 found that in the presence of a reducing agent (aluminium amalgam) 

 no tar formation takes place, but considerable quantities of aceton are 

 formed. 



Confining our attention for the moment to the hexoses, it is very in- 

 teresting that in the glucose series at equilibrium ketoses and aldoses are 

 formed in about equal quantities ; of the aldoses, glucose and mannose there 

 is present five times as much of the former as of the latter. Similarly in 

 the galactose series over 90 per cent of the sugars present is d-galactose. 

 These facts are of direct bearing on the problem of the synthesis of dif- 

 ferent sugars in nature. It gives a clue as to why allose, latose and talose 

 have not been found in nature : this presumably also applies to gulose 

 and idose and makes the presence of these sugars in formose highly im- 

 probable. These investigations of Nef ofifer the first chemical evidence 

 of the fact that certain of the hexose sugars are apparently more stable 

 or that the tendency' of formation of certain ones is greater than of 

 others. Why this is so, why the space relationship of one sugar makes 

 for greater stability than another we are as yet unable to say. But it 

 is significant that the proportions of the various sugars found in both 

 the glucose and galactose are, at least, of the same general character as 

 those found in nature. It remains to be determined whether there exist 

 certain enzymes which are capable of the same reactions as are produced 

 by the alkalies. Recently Spoehr and Wilbur •*•' have found that disodium 

 phosphate and neutral mixtures of phosphates produce the same isomeriz- 



ing effects. 



Nef carried out a similar line of reasoning with the pentose sugars and 

 concluded that only 12 pentoses can be formed in formose. 



In considering this phase of the Baeyer theory which deals with the 

 condensation of formaldehyde to sugars as was first discovered by 

 Butlerow, there remains the question whether this method of synthesizing 

 sugars has any application to the process taking place in the plant. The 

 methods thus far discussed all postulate the action of more or less strong 

 alkali on the formaldehyde. There is no evidence that the reaction of 

 the cell sap or of protoplasm even approaches that of the solutions used 

 in the methods of preparing formose, although protoplasm is probably 

 sUghtly alkaline. 



" Spoehr and Wilbur, Carnegie Inst. Washington Yearbook 1925, p. 158. 



