176 TRANSPIRATION AND ASCENT OF SAP 



CH. 



noticeable, owing to the presence of chlorophyll cor- 

 puscles embedded in them. It seemed allowable to assume 

 that, where the component cells are so completely disin- 

 tegrated as is indicated by this observation, all the sap 

 of their vacuoles must be shed into the expressed fluid ; 

 or at least there would be no reason to suspect a difference 

 in composition between the latter and the sap which 

 remained behind in the organ. 



Fairly early in this research, however, observations were 

 made which, in the light of subsequent work, might have 

 borne a different interpretation. For example, when leaves 

 were exposed to the vapour of chloroform, it was found 

 that the sap was pressed out with much greater ease, and 

 its freezing-point was very much lower, than that of the 

 sap coming from the untreated leaves. 



This may be illustrated by the experiments made on 

 the sap of leaves of Hedera helix, shown in Table 20. 



Table 20. 

 Sap ikom Chloroformed and Fkesh Leaves of Hedera helix. 



No. of 

 Expt. 



Description of Sap. 



227 

 229 



232 



233 



Pressed from untreated leaves on gathering . 

 Same sap as in 227 to which a few drops of 



chloroform had been added, kept 24 hours . . 

 From leaves similar to those used in 227 after 



they had been 24 hours in the dark 



From leaves similar to those used in 227 after 



they had been 24 hours in the dark and in 



chloroform vapour 



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. Experi- 

 ment 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 the 



