Dixon and Axkins — Osmotic Pressures in Plants. 



423 



This may be illustrated by the experiments made on the sap of leaves of 

 Hedera Helix, sliown in table above (p. 422). 



A comparison of experiment 227 -with 229 shows the increase of the 

 depression of freezing-point we may expect from the saturation of the sap 

 with chloroform. Experiment 232 is added by way of comparison to indicate 

 the change in freezing-point which is experienced by the sap of untreated 

 leaves when kept for twenty-four hours in the dark. The depression of the 

 sap pressed from tlie chloroformed leaves is evidently much greater than can 

 be assigned to the action of the chloroform on the sap, or to the spontaneous 

 changes in the cells of the leaves, which appear in experiments 229 and 232 

 respectively. 



Another result which could be interpreted in the same sense was furnished 

 by two experiments on the sap of leaves of Ilex Aquifolium. In these it was 

 found that, if the leaves were killed by heat in a saturated atmosphere, they 

 yielded a sap having a much greater depression of freezing-point than that 

 pressed from similar leaves which had not been heated. 



Again, we found that, if a weighed quantity of leaves be desiccated, 

 reduced to powder, and again made up to the original weight with water, the 

 sap pressed from the mass will have a much greater depression than that 

 pressed from tlie fresh leaves without passing through this treatment. This 

 point is borne out by the following experiments : — 



Hedera Helix. 



In experiments 436 and 437 the specific electrical conductivities of tlie 

 saps at 0° 0. were also determined, and were found to be respectively 0'00485 

 and 0'00623. This shows that the quantity of electrolytes in the sap pressed 

 from the desiccated leaves has increased approximately proportionally with 

 the other dissolved substances. 



3r2 



