W. A. Davis and G. C. Sawyer 357 



by the fact that in Brown and Morris' experiments the heating up of 

 the leaves in drying was much slower and allowed far more diastatic 

 action to occur than in Kluyver's experiments. Kluyver especially 

 points out that his leaves, which were dried in thin layers in a baker's 

 oven heated to 105°, were exposed to the drying process during only 

 5 to 10 minutes. We have ourselves made several experiments with 

 Tropwolum leaves dried rafidly in a steam oven and by our own methods 

 have invariably found no maltose to be present, just as in the case of 

 the same leaves dropped into boiUng alcohol. 



From the above facts we have concluded that the maltose which 

 was undoubtedly present in Brown and Morris' experiments in relatively 

 large amounts and in Kluyver's experiments in far smaller proportions 

 owing to the greater rapidity of drying, was not formed in the tissue of 

 the leaf as such during growth, but was produced by the degradation 

 of starch by the diastatic enzymes remaining after the nialtase in the 

 leaf had been destroyed in the first stage of the drying process. As 

 regards the mechanism by which starch is utilised in the plant when, at 

 the end of the day, the reserves in the leaf are called upon, ire consider 

 that the starch is hydrolysed conifletehj to dextrose by the leaf enzymes, 

 which resemble the enzymes of Aspergillus oryzae in containing an 

 abundance of maltase. Brown and Morris' main view that the starch 

 is utihsed by a purely enzymic process seems to us perfectly correct, 

 but we regard the enzymic degradation as stopping, not at maltose, 

 as supposed by Brown and Morris, but at the stage of dextrose, the 

 final product of starch hydrolysis. One of us has shown (Davis, 

 Chemical World, 19U, p. 271) that yeasts which do not contain the 

 enzyme maltase, for example, S. anomalus and S. exiguus, are quite 

 unable, even when in the throes of starvation, to make use of maltose 

 in the solution in which they are growing ; similarly we find that Tortda 

 monosa, which does not contain invertase, is unable to make use even 

 of cane sugar. Plant tissue, we consider, in exactly the same way 

 before it can utilise starch, maltose or saccharose, for purposes of growth, 

 must break these substances down to the simple hexoses by enzyme 

 action. This view explains the significance of the fact that the sugars 

 in the stalks of all the plants we have examined consist largely of the 

 simple hexoses ; these sugars are capable of being directly assimilated 

 by the cambium layer of the stems or by other growing points. The 

 necessity of transformation of saccharose into invert sugar thus explains 

 the almost ubiquitous presence of invertase in the plant, except in 

 such storage reservoirs as the mangold root, where cane sugar is 

 permanently housed. 



