THE CARBOHYDRATES OF THE ANGIOSPERM LEAF 5 



great. Adopting as a unit the amount of maltose, ex- 

 pressed in grammes, which 10 grammes of the air-dried 

 leaf will produce from soluble starch by hydrolysis in forty- 

 eight hours at 30 C., they compiled a table in which the 

 relative diastatic activities varied from 240-30 for Pisum 

 sativum to 0-267 for Hydrocharis morsus-rance. The latter 

 is, however, unusually low, and this abnormality was subse- 

 quently found to be due to the marked inhibitory action of 

 the tannin contained in the leaves. With the exception of 

 the case of Hydrocharis, far more diastase was present in the 

 leaves examined than was requisite to transform all the 

 starch in them within a moderate period of time. Thus, 

 leaves of Pisum sativum contain sufficient diastase to 

 hydrolyze twenty-four times their own dry weight of 

 starch within forty-eight hours. Comparative experiments 

 showed that this represents about one-third the activity of 

 an average quality of barley malt. The Leguminosse have 

 high diastatic activity ; they also form starch readily. On 

 the other hand, certain of the Liliaceae form little or no 

 starch, and are very poor in diastase. Thus there is a 

 relation between the starch-producing and the starch- 

 dissolving power of plant tissues. The presence of tannin 

 is not as effective an inhibition in the living plant as in 

 dried leaves, for during life it is retained in separate cells 

 or portions of cells. 



Further experiments showed that the diastatic activity 

 of leaves undergoes periodic variations, increasing during 

 darkness or when the sugar content of the leaves is small. 

 Brown and Morris brought forward an hypothesis to account 

 for the production of the enzyme by the protoplasm, basing 

 it on the observed relation between diminution in sugar 

 content and increase in diastatic activity. They regard a 

 poor sugar-supply as a hunger stimulus, prompting the 

 protoplasm to form or liberate diastase. It was, however, 



