Jan., I92i] WIGGANS — OSMOTIC CONCENTRATIONS OF GUARD CELLS 3 1 
ordinarily high osmotic concentration for the guard cells when the stomata 
are open as compared with the osmotic concentration in the epidermis and 
leaf parenchyma. He found little or no difference between the osmotic 
concentration of the guard cells and that of the epidermis of the leaf 
parenchyma when the stomata are closed. The latter tissues always 
remained constant in their osmotic pressures. Table i will serve to illus- 
trate the extreme differences in osmotic concentration which Iljin found 
between the guard cells and the parenchyma of the leaves. 
Table i 
Pressure in Atmospheres 
Name of Plant 
Guard Cells 
Parenchyma 
over 80 
22.5 
108 
22.5 
Centaurea orientalis 
537 
21.4 
Centaurea orientalis 
98 
under 24 
Iris pumila 
90 
" 24 
98 
13 
Eryngium campestra 
98 
19.1 
Verbascum Lynchnitis 
80.5 
17.9 
Veronica incana 
90 
45(?) 
The concentration in all cases is expressed as pressure in atmospheres. 
The greatest difference in concentration between the guard cells and the 
parenchyma always occurred when the stomata were open to the greatest 
width. No determinations were made before the stomata were open in 
the morning, but the observations made at 8 a.m., 12 noon, 4 p.m., and 
7:30 p.m. showed a marked decrease in the difference in osmotic concentra- 
tion from 8 a.m. to 4 p.m., at which latter time the concentration was the 
same in all tissues. 
Iljin does not explain his method of calculating osmotic concentration 
in atmospheres of pressure. However, the osmotic concentrations reported 
in this paper will be calculated according to the tables and formula given 
by Jones (1907). All of Jones' calculations of osmotic concentration are 
based on the depression of the freezing point and the concentration of the 
solution. He gives table 2 for calcium chloride. 
Table 2 
Lowering of 
Concentration Freezing Point Atmospheric Pressure 
.102 mol 505 6.08 
•153 752 9-054 
.204 I.0I2 12.184 
.255 1.267 15.255 
.306 1.537 18.505 
•408 2.104 25.332 
.510 2.681 32.279 
•612 3-348 40.31 
I -000 6.345 76.394 
