Permeability 189 
parenchyma and medullary rays. Minimum values were found in 
the lower epidermis of the leaf in Helleborus and Fagus and in the 
cortex of the leaf stalk in Urtica. The mean values found by Ursprung 
and Blum for Fagus sylvatica are shown in the following table. The 
osmotic concentrations are given as concentrations of potassium 
nitrate. 
Table XXI 
Mean Values of the Osmotic Concentrations in the Cells of 
Different Tissues of Fagus sylvatica 
(Data from Ursprung and Blum) 
Organ 
Epidermis 
Spongy 
tissue Palisade 
Outer 
cortex 
Inner 
cortex 
Phloem 
paren¬ 
chyma 
Com¬ 
panion 
cells 
Cambium 
Xylem 
parem- 
chyma 
Cortical 
medul¬ 
lary 
rays 
Xylem 
medul¬ 
lary 
rays 
Leaf 
lamina 
} 0-371 
0*571 I*Oiy 
— 
— 
— 
— 
— 
— 
— 
Branch 
— 
— — 
0*667 
0*671 
o-573 
0*721 
0*64 
i*oo8 
0*808 
o-954 
Stem 
— 
— — 
0*696 
0*696 
0*562 
0*746 
0*638 
0*963 
0*929 
0*921 
Root 
— 
— — 
0*65 
0*671 
0*583 
0*70 
0*625 
o*979 
— 
— 
Differences of Osmotic Pressure in Species 
of Different Habit 
While the numbers quoted in the preceding section are 
sufficient to show that great variations of osmotic pressure may 
occur in different cells of the same species, it is certainly true that 
differences in the osmotic concentration of cells occur in relation to 
specific differences. Such differences are frequently related to the 
habit of the plants under consideration. Thus in succulents the 
osmotic pressures of the cells are relatively lower than in meso- 
phytes (Ursprung and Blum, 19160). In an investigation on the 
plants growing in the deserts of Arizona, Harris, Lawrence and 
Gortner (1916) found considerable variation of osmotic concentra¬ 
tion of different species, the different groups in order of increasing 
concentration being (1) winter annuals, (2) perennial shrubs, 
(3) dwarf shrubs and half shrubs, and (4) shrubs and trees. In a 
later investigation on the osmotic concentration of the leaf sap of 
plants from the Blue Mountains of Jamaica, Harris and Lawrence 
(1917 b) found that the osmotic concentration of the leaves of woody 
plants was greater than that of leaves of herbaceous plants, and the 
same result was obtained with plants of the Arizona deserts and the 
north shore of Long Island (Harris, Gortner and Lawrence, 1921 a, 
1921 b). Ursprung and Blum (1916 a), however, found the osmotic 
concentration of the palisade cells of Urtica dioica about the same 
