230 Scientific Proceedings, Royal Dublin Society. 



To quote examples illustrating this point : — 



Table I. 

 Ilex Aquifolimn. 



In this table, as throughout the paper, under A is given the depression 

 of freezing-point observed by the thermo-electric method, under P the 

 osmotic pressure calculated from it and under If the mean molecular weight of 

 the dissolved substances producing the osmotic pressure, calculated from the 

 dry -weight of the dissolved substances in a certain weight of sap and from 

 the freezing-point. It may be noted here that the osmotic pressures 

 calculated in this way will be somewhat lower than those obtained by the 

 plasmolytic method, as in this case the osmotic pressure is that which the 

 dissolved substances exercise at 0° C, while when measured by plasmolysis the 

 osmotic pressure found is that exerted at ordinary room temperature, viz., 

 about 15° C. 



With regard to the mean molecular weight of the dissolved substances, 

 the presence of colloids which are not removed by filtration will tend 

 to make our determinations too high. In any case the method for deter- 

 mining it, the usual chemical method, is not one of great accuracy ; and 



