Dixon and Atkins — Variations in Osmotic Pressure, ^c. 241 



In addition to the depression of freezing-point A, the osmotic pressure 

 P, and, where filtration could be accomplished, the mean molecular weight M 

 of the dissolved substances in these tables, is given a record of the weather on 

 the day previous to and at the time of gathering. At the outset it was 

 expected that the conditions of lighting, humidity, &e., would have had a 

 large influence on the results, especially in the ease of the leaves taken from 

 the south aspect. As will be seen, however, this expectation was not realized, 

 or at least the influence of these factors was by no means very marked. 



In each ease the depression of freezing-point of the sap of the ultimate 

 leaves is less than that on the penultimate leaves, and generally the sap 

 of the younger leaves has a smaller depression than that of the older. The 

 observations on October 16th, 1910, show that smaller leaves, although older, 

 may have a smaller depression than larger leaves formed at a later date. 

 This is possibly due to the fact that these smaller leaves are more or less 

 covered over by the larger and often younger ones of adjacent shoots. 



The growth of Hedera shoots is more continuous than that of Ilex shoots, 

 and the limits of each growth are not defined by a crowd of scars as they are 

 in the latter plant ; consequently it is not so easy to keep the leaves of various 

 ages apart. Furthermore, the observation of October 16th, Table I, shows 

 that the size of the leaves has an influence upon the eryoscopic value of the 

 sap. Hence it was deemed best to collect on each date full-grown mature 

 leaves, and to make the determination of the freezing-point of the sap 

 pressed from these. In the following table these determinations are given 

 for the plants grown in both the south and north aspects. 



[Table III. 



2p2 



