220 



Scientific Proceedings, Royal Dublin Society. 



described. It may be pointed out tbat the osmotic pressure determined in 

 this manner is the osmotic pressure of the sap at 0° C, and consequently will 

 be somewhat lower than the osmotic pressures determined by the plasmolytio 

 method, which are usually measured at about 15°-20° G. 



Buds of Syringa vulgaris gathered during the autumn of 1909 and during 

 the winter 1909-10 yielded no sap, or at least none in sufficient quantities for 

 tlie experiment. Consequently, during that period no determinations were 

 possible. It was not till February 19, 1910, that a sufficient amount (viz., 

 about 2 c.c.) could be pressed from a handful of buds. With this date the 

 determinations begin. 



The following table shows the depression of freezing-point A, the osmotic 

 pressure P calculated from it, and the mean molecular weight M of sub- 

 stances dissolved in the sap. The last figure is derived from the depression 



of the freezing-point and the dry weight of the dissolved substances. When 

 no molecular weight is given, the expressed sap was too viscid to allow of the 

 removal of colloids and undissolved substances by filtration. Consequently, it 



