Dixon and Atkins — Osmotic Pressures in Plants. 



453 



Table HI. 

 Ilex aquifolium : Leaves. Concentration and Ages. Mean Values. 



Ilex aquifolium : Roots. 



There is considerable difficulty in examining the sap of tlie roots of most 

 plants tlirougliout tlie year. The amount of roots required for each set of 

 measurements is considerable, and unless the plant is very vigorous it will 

 not survive this deprivation very often. Of the plants examined we found 

 Ilex aquifolium the most resistant to such treatment, and, consequently, we 

 selected it for this work. 



With regard to the preparation of the roots, it is necessary tliat they 

 should not carry on their surface any of tlie unabsorbed water of the soil; 

 at the same time, care must be taken tliat water is not abstracted from them 

 by drying. The method of bringing the roots to a uniform condition 

 before freezing and extracting the sap was to immerse them for a few minutes 

 in a large quantity of air-dry soil, and change the soil round them a few 

 times. In tliis way moisture and extraneous substances were removed from 

 their surfaces, while the soil, not being very dry, did not tend to extract 

 water from the tissues. 



The results of the experiments are shown in Table IV. In this the thin 

 roots, under 2 mm. in diameter, are marked 0, those over 2 mm. in diameter 

 A, while, when the sample from which tlie sap was extracted was a mixture 

 of roots of 4 mm. and under, it is denoted by B. These letters are also 

 attached to the points on the graphs in fig. 3, and indicate the nature of the 

 sample from which the results plotted were obtained. 



SCIENT. PROC. R.D.S., VOL. XIV.. NO. XXXIV, 4 C 



