n6 SCIENCE PROGRESS 



from formaldehyde to a glucose is then a step which can be 

 produced in the test tube by the use, for instance, of various 

 inorganic reagents such as calcium hydrate. 1 But in some very 

 important papers 2 in which the evidence to be obtained from the 

 distribution of sugars within the leaf is considered, the con- 

 clusion is reached that the first sugar in the series of up-grade 

 sugars is the di-saccharose cane sugar, a conclusion which is 

 more difficult to reconcile with the statement that formaldehyde 

 is the first detectable compound in the transition from carbon 

 dioxide. 



Considering the question from our present specialised view- 

 point, light may be thrown on the contradiction if we consider that 

 the series of sugar transitions are probably reversible reactions 

 and attempt to obtain light upon the up-grade series by consider- 

 ing the well-established steps in the hydrolysis of the starch 

 molecules with the aid of enzymes as it occurs under in vitro 

 conditions. 



The stages in the process are represented in the following 

 scheme : 



(by diastase [amylase]) 



Starch > dextrin 



(by diastase [dextrinase]) 



dextrin > maltose 



(by maltase) 

 maltose — > glucose 



It will be seen that cane sugar does not figure in this series 

 at all ; cane sugar, a di-saccharose, is itself broken down by 

 the action of sucrase (or invertase) into the mono-saccharoses 

 glucose and fructose. Beyond ^-glucose the catalytic reactions 

 by which the sugar is split up into simpler molecules are still 

 unknown owing to the difficulty in carrying out the process 

 away from the plant tissues. Glucose can be split up into 

 carbon dioxide and water, it is true, by the action of three purely 

 inorganic catalysts acting in series, 3 but this affords no proof 

 that the reactions in the plant proceed in the same manner. 



Zymase will give alcohol and carbon dioxide when in contact 



1 Fischer, loc. cit., p. 3. 



2 Brown and Morris, " A Contribution to the Chemistry and Physiology of 

 Foliage Leaves," /. Chem. Soc, 1893, 63, p. 604; Parkin, Biochemical Journal, 

 vol. vi. p. 1. 



3 See Euler, General Chemistry of Enzymes, Eng. trans, by Pope (pub. Wiley 

 & Sons), p. 52. 



