150 



Scientific Proceedings^ Royal Dublin Society. 



Fresh leaves were pressed at various times duriug February and March, 

 1912, and determinations of reducing power, rotatory angle, osmotic pressure, 

 mean molecular weight, and electrical conductivity were made. It may here 

 be remarked that though these values are recorded as being roughly com- 

 parative, they are neither absolute nor even strictly comparative values. 

 For it has been shown by Dixon and Atkins (10) that the true concentration 

 of the cell-sap is only obtained after the protoplasm is rendered permeable 

 by immersion of tlie tissues in liquid- air before pressing. 



Under A, P, M and x 10* in the following table are recorded the freezing- 

 points determined by the thermo-electric method of cryoscopy (Dixon and 

 Atkins (9)), the osmotic pressures calculated from them, the mean molecular 

 weights obtained from the freezing-point and solid residue determinations, 

 and the electrical conductivities: — 



It is clear that the low values of the mean molecular weiglits exclude 

 the presence in quantity of the hexoses or higher sugars. With the excep- 

 tion of No. 443, the extracted dried leaves, the values found lie fairly close 

 together. 



It will be noticed that the electrical conductivities increase towards the 

 close of the spring. This is probably an apparent effect, due to the greater 

 number of young leaves employed. 



The sugar analyses showed that the amounts of sugar present were not 

 very great. In one case (No. 44b), 0*48 grm. of dextrose and levulose was 

 found per 100 c.c. of sap. with 0-65 grm. of cane-sugar. Yet this sap gave the 

 strong reducing action and inhibited Hedera oxydase. In another case 

 (No. 448) 3-32 grm. of dextrose were present, 190 grm. of levulose, and a 

 small quantity of cane-sugar. Owing to the absence of starch in the leaves, 

 these calculations were made on the assumption that no maltose was present. 

 In making the analyses, the sap colloids were removed by basic-lead acetate 



