96 Scieniific Proceedings, Royal Dublin Society. 



clumping of the colloids during the exposure of the leaves to the anaesthetic. 

 It is not improbable, however, that it is associated with an increase in the 

 concentration of the hydrogen ion as a result of the stimulation of respira- 

 tion (12). In a similar way, the greater activity shown by the untreated 

 sap (Table V) would be due to a partial precipitation of the colloids during 

 the freezing of the leaves ; as ice separates out in the cell vacuoles, the 

 hydrogen ion becomes more concentrated, and will, as Harvey (8) has shown, 

 bring about a precipitation of some of the colloids. The temperature to 

 which the leaves are exposed must clearly be an important factor, according 

 to this view, in determining the activity of the enzyme in the sap after its 

 extraction. 



The permanence of the inhibition would on this assumption depend on 

 whether the colloid (anti-enzyme) on which the enzyme was removed was 

 reversibly or irreversibly precipitated. It may be that the activity of the 

 enzyme in the living cell is regulated by some such means. 



It has been demonstrated by numerous investigators that sucrose 

 accumulates in the assimilating cell during photosynthesis, and, as this 

 accumulation of sucrose is of a very pronounced character, it is obvious that it 

 cannot be stored in the presence of an enzyme actively engaged in bringing 

 about its hydrolysis. It would follow, therefore, that either invertase is 

 absent from the vacuoles where storage takes place, or else a mechanism is 

 present whereby its activity is controlled ; that the latter explanation is more 

 probable is indicated by the experiments recorded in this paper. 



Until such factors as temperature, traces of alkali dissolved from the 

 glass, changes in the hydrogen ion concentration of the sap, and the effect of 

 shaking have been considered, further discussion cannot be profitable. 



Opportunity for this research was provided by a maintenance grant from 

 the Department of Scientific and Industrial Research. 



The writer wishes to express his indebtedness to Prof. H. H. Dixon, f.k.s.> 

 under whose direction the work was carried out. 



