188 
Walter Stiles 
volving material from 12 species of trees, of the osmotic pressures of 
expressed saps from leaves inserted at different levels, and found 
almost without exception that the osmotic pressure is higher in leaf 
cells the higher the insertion of the leaf. Some of their results are 
shown in the following table. The slight exception recorded in the 
table in the case of Betula lutea might easily be due to experimental 
error. 
Table XX 
Osmotic Pressure of the Sap of Leaves inserted at different 
Levels. (Data from Harris, Gortner and Lawrence) 
Height in 
Osmotic pressure 
Species 
feet 
in atmospheres 
Betula lutea 
66 
15-55 
52 
16-01 
39 
15-12 
25 
14-11 
11 
12-63 
Quercus Prinus 
47 
20-23 
36 
20-08 
30 
19-72 
19 
19-57 
Robinia Pseudacacia 
5i 
12-44 
39 
11-07 
29 
10-87 
9 
io -68 
An extensive series of observations made by Ursprung and Blum 
(1916 a) by means of the plasmolytic method scarcely supports the 
conclusions of Harris, Gortner and Lawrence, but the species used 
were not the same; they were: Helleborus fcetidus, Urtica dioica, 
Fagus sylvatica, Sedum acre and Funaria hygrometrica. Thus in the 
case of Fagus sylvatica Ursprung and Blum could find no connexion 
between the osmotic pressure of the cells and the height from the 
ground of the leaves containing them, while generally the cells of 
the same tissue (root, stem, leaf stalk and lamina) have a higher 
osmotic pressure the nearer they are to the base of the organ. Other 
conclusions of Ursprung and Blum are that cells of the same layer at 
the same height from the ground have approximately the same os¬ 
motic pressure if they are not too far apart, but neighbouring cells 
belonging to different layers may differ considerably in their osmotic 
pressures. In the cells of younger leaves the osmotic pressure was 
less than in older leaves. 
The highest values for the osmotic pressure were found in Helle- 
borus and Urtica in the palisade. The same was the case with Fagus, 
but here equally high values were found in the palisade, wood 
