84 



Scientific Proceedings, Royal Dublin Society. 



As soon as the freezing-point determinations were made the saps were 

 stored for approximately twenty-four hours at 29° in a thermostat. 



The increases in depression are shown in Table I in the last column 

 [A. - Ai]. 



In the absence of other changes affecting the depression, this increase 

 should afford a measure of the sucrose inverted. 



Table I. 



That sap pressed from tissues which have been exposed to intense cold 

 has a much greater depression of the freezing-point than that from untreated 

 material has been already demonstrated by Dixon and Atkins (5), and does 

 not call for further comment. On the otlier hand, it will be noted that the 

 increase in depression after storage is as great in the sap pressed from 

 untreated leaves as in that from the frozen material. 



Assuming the increase in depression is proportional to the sucrose- 

 content of the sap, this might be due to the greater permeability of the 

 protoplasm to sucrose than the other solutes ; or else that in the pressing of 

 the untreated leaves the rupture of the cells has set free the contents of the 

 larger vacuoles, where possibly the concentration of sucrose is greater than in 

 the protoplasm. 



In Table II the results of a somewhat similar experiment are shown. 

 Sap pressed from leaves, both untreated and frozen, was again employed, but 

 in this case, with a view to determining if the acidity of the sap was 

 responsible (by hydrolysing the sucrose) for any of the rise in depression on 

 storage, a sample of each was immersed with its containing test-tube for one 

 minute in boiling water ; a reflux condenser was fitted to each test-tube. 



