120 SCIENCE PROGRESS 



this direction. In leaves such as the snowdrop, where cane 

 sugar seems to be stored to the complete exclusion of starch, 1 

 the enzyme disastase is yet present, and leaf extracts exert 

 a rapid hydrolytic action on starch. No maltase however 

 can be extracted, and possibly in the absence of this enzyme 

 no maltose can be formed, 2 and therefore no starch. In cases 

 where maltose is presumably freely formed, that is, on this 

 view, in all cases where starch is subsequently formed, it is 

 difficult to know at present whether the often reported presence 

 of emulsin in such leaves may or may not have significance. 



From starch to maltose the down-grade stages are by no 

 means clear. As was suggested in the scheme given earlier, the 

 process probably takes place in two main stages, associated with 

 different enzymes or more probably groups of enzymes. At 

 present it is perhaps only worth pointing out that the statements 

 in the older literature 3 as to a portion of the starch molecule 

 incapable of complete hydrolysis, arose from a mistaken inter- 

 pretation of an equilibrium point which is very definitely 

 obtained in the hydrolysis of dextrin to maltose. 4 



It is not unnatural that it should have proved impossible as 

 yet to form starch granules by merely reversing the enzyme 

 mechanism in vitro, seeing that the process in the plant is 

 apparently so complicated that it never occurs but in association 

 with a controlling plastid. Everything points to a complicated 

 process involving the use of a series of enzymes under close 

 protoplasmic control, and presumably held to definite places in 

 the internal surfaces of the solid phase of the granule — indeed, 

 so carefully controlled apparently that they are not liberated in 

 death, so that I do not think it has ever been found possible to 

 detect appreciable disappearance of starch from the plastid after 

 death produced by chloroform or other anaesthetic, although the 

 diastatic activity of an aqueous extract of such a leaf seems to 

 be fully adequate to the hydrolysis of the amount of starch 

 present. 5 



In view of these facts one has to interpret very tentatively 



1 Parkin, loc. cit. 



1 The statements as to the distribution of enzymes in the snowdrop leaf are 

 based on work done in this laboratory, but not yet published. 

 3 See for instance, Reynolds Green, Fermentation. 

 * Bayliss, loc. cit., Chap. VI., p. 55 (1st ed.). 

 5 See Brown and Morris, loc. cit., p. 651, discussion of Wortman's results. 



