Dixon and Ai'Kins — On Osmotic Pressure in Plants, ^c. 30l 



At the eud of the experiment, some of the leaves in sample b had bei^un 

 to wilt. It is evident that in this case the concentration due to loss of water 

 was responsible for the greater part, but not all, of the rise in osmotic pressure. 



In the figures given above (see Table VII.) experiments Nos. 31 and 32, 

 leaves gathered in the evening were set aside, kept from light, and pro- 

 tected from evaporation, and were then compared with others gathered next 

 morning. On examination the evening sample gave a greater depression of 

 freezing-point. It is evident that some or all of this increase might be due 

 to some change taking place during the night in the gathered leaves. 



Experiments 41 and 42 bear upon this point. In these it is shown that 

 the keeping, although introducing a change, will not account for the total 

 difference observed. The loaves gathered, after seven hours' insolation, were 

 divided into two lots — a and b. From a the sap was pressed immediately, 

 and kept over till next morning for investigation. Lot b was set aside 

 uninjured, protected from light and evaporation till nest morning. Its sap 

 was then pressed and investigated. The figures are repeated here. 



Table XV. 



Si/ringa vulc/ans : leaves. 



During the night changes have gone on in the sap of the intact leaves 

 which did not progress so rapidly in the expressed sap. Observations 64 

 and 65 afford a similar instance, in these experiments the leaves were 

 gathered on the afternoon of the 14tli. Of these two lots, a and b, were 

 formed by dividing eaoli leaf down the midrib, which was always rejected. 

 Tlie sap of lot a was extracted and examined immediately. Lot b was 

 kept over till the afternoon of the 15th. Its sap was then expressed and 

 examined. The results substantiate the former observation^ and, as the 

 difference in both cases is similar, indicate that considerable changes in 

 osmotic pressure did not occur in the pressed sap of No. 41. 



3b2 



