90 



Scientific Proceedings, Royal Dublin Society. 



For comparison, the freezing-points of the saps which had been boiled on 

 the day of extraction, and to which 0'33 gm. of inverfcase had been added, 

 are also shown. The increase in depression, corrected for dilution by the 

 iuvertase added, is given in the last column. 



Table V]. 



It will be observed that the inversion of the sucrose in the sap was not 

 complete after 120 hours' storage at 29"". 



It may be objected that a destruction of hexoses by respiratory enzymes 

 would afford an explanation of the apparent inhibition of hydrolysis recorded 

 in figures 1, 2, and 3. It must be admitted that such a view cannot be positively 

 set aside ; but the striking similarities in the freezing-points recorded under 

 A,j of Table VI for the saps (to each of which -33 gm. of invertase solution 

 was added) which were boiled on the day of extraction, and in which the 

 activity of all the enzymes was destroyed, to those in which the enzymes 

 were not killed until a period of 120 hours had elapsed, do not point to 

 such a destruction of sugar. If this destruction of hexoses by respiratory 

 enzymes had taken place during storage in the saps which were not 

 boiled on the day of extraction, it would presumably result in their showing 

 a smaller depression of the freezing-point than that shown by the samples in 

 which the enzymes were destroyed by boiling on the day the sap was extracted 

 from the leaves. That this is not so, as the figures recorded under A24 in 

 Table VI indicate, does not exclude the possibility of a destruction of hexoses, 

 but renders it very improbable. 



The interpretation of the decrease in depression sliown in figs. 1 and 3 of 

 the frozen and untreated saps is not clear ; it is possibly due to a condensa- 

 tion of the hexoses of the sap to form sucrose. Eobertson, Irvine, and 

 Dobson (11) observed an association of this nature while working with sludges 

 prepared from the leaves of Beta vulgaris. This condensation would, of course, 



