Dixon and Atkins — Osmotic Pressures in Plants. 



377 



of carboliydrates passing up through the tracheae in the transpiration stream 

 has about the same freeziug-point as a 0-25 per cent, solution of glucose, or a 

 0'50 per cent, solution of sucrose. The concentrations of the carbohydrates 

 of the root approximated to those of 0-3 per cent, solution of glucose, or of 

 0'7 per cent, of sucrose. 



These observations strikingly negative Sachs' view that the stream rising 

 from the roots to the leaves during transpiration is to be regarded as a very 

 dilute solution of salts only. 



It is interesting to note how much more concentrated the sap of the 

 vacuoles of the cells of the leaves was at the same time. This sap was 

 extracted by pressure from leaves which had been treated with liquid air to 

 render their protoplasm permeable without affecting the concentration (1). 



Contemporaneously with the experiments on Acer jKeHdojilatanus similar 

 measurements were made on the sap of Populus alba, and are recorded in 

 Table III. 



Table III. 



Sap of Populus alba. August 28, 1913. 



In this case the sap centrifuged from the traclieae of the stem and the 

 root gave no direct reaction with Fehling's solution. Evidently neither 

 glucose nor maltose was present. On inversion, however, a noticeable reduc- 

 tion took place, indicating the presence of sucrose to the amount of about 

 0'5 per cent, and 1 per cent, respectively in the stem and root. 



The sap from the cells of the bark of stem and root, and from the 

 leaves examined at the same time, showed, as appears above, much higher 

 concentrations. 



It was then determined to investigate the concentration and constituents 

 of the wood sap at different seasons of the year, and to see if variations of 



