6 



Scientific Proceedings^ Royal Dublin Societij. 



Method applied to the Estimation of the Sucrose content of &p5. 



It has been demonstrated by Dixon and Atkins (4) that the application of 

 intense cold renders tissues permeable, and so provides a means of extracting 

 by pressure a representative sample of the sap. Jn tlieir work liquid air 

 was employed ; as this, however, was not available, a freezing mixture of salt 

 and ice has been employed. That the temperature thus oljtained is capable of 

 rendering the tissues permeable is shown elsewhere. 



An experiment carried out on the leaves of Galanthus spicatus will 

 illustrate the method adopted for determining the sucrose-content, and will 

 give some idea of the accuracy that may be expected of it. 



The leaves were gathered at 9.30 a.m., April 26tli, from two clumps of 

 this plant growing side by side. Erom one clump light had been excluded 

 for live days. The leaves were then packed in large test tubes, which, after 

 corking and sealing with plasticine, were submerged in the freezing 

 mixture [- 16°] for two hours. On removal of the corks the tissues were 

 found to be frozen solid ; they were not, however, taken from the test tubes 

 till they were somewhat thawed. On withdrawal of the material it was 

 wrapped in linen, and pressed in a vice between two silver discs ; about 30 c.c. 

 were collected from each sample. In order to check the immediate activity 

 of the enzymes, the sap was collected in tost tubes and jacketed in ice. 



Fifteen cubic centimetres of each sample were then boiled to kill the 

 enzymes in half-inch test tubes, fitted with reflux condensers, by immersion 

 for one minute in a brine bath. The freezing-points of the sap before and 

 after this treatment are shown in Table IV ; a slight lowering of the depres- 

 sion took place in both samples. 



Table IV. 



Description of Sample. 



S.ip pressed from exposed leaves, 



of sap before boiling 

 and filtering. 



Sap pressed from leaves coveied for live days. 



O/o.-) 



OiOS" 



of sap after boiling 

 and filtering. 



0-7i8° 



0'69S° 



Two test tubes (about 10 c.c. capacity), each containhig 5 gm. of the 

 boiled and filtered sap of each sample, were tlien immersed in a freezing 

 bath [- 2=]. 



