AMERICAN JOURNAL OF BOTANY 
[Vol. 8 
of the sap was made under a pressure of 50,000 pounds; conditions which 
would yield the highest values. 
Table 2. Zehrina pendula 
No. of Exp. 
Osm. Pr. in Atm. with 
Sucrose 
Osm. Pr. in Atm. with 
CaCI.2 
Average | Cryoscopic 
No. I 
No. 2 
No. 3 
No. 4 
4-233 
4. 121 
4.188 
4.211 
4.480 
4.650 
4.704 
4-569 
4-356 
4.385 
4-446 
4-390 
5-173 
6.425 
5-714 
5-293 
Table 3. Iresine 
No. of Exp. 
Osm. Pr. in Atm. with 
Sucrose 
Osm. Pr. in Atm. with 
CaCl> 
Average Atm. 
Piasmolytic 
Atm. Cryoscopic 
No. I . ! 6.720 
No. 2 6.496 
No. 3 6.944 
No. 4 1 6.329 
7.078 
7.IOI 
6.809 
6.918 
6.899 
6.798 
6.876 
6.623 
8.300 
9-443 
7-981 
8.016 
A comparison of the various data indicates that the cells must permit of 
the entrance of CaCl2 more readily than the sucrose, since the osmotic- 
pressure values as determined are higher when the plasmolyzing solution is 
CaCl2 than when the solution is sucrose. The values as determined by 
the cryoscopic method are in all cases higher than the osmotic-pressure 
values as obtained from the piasmolytic method. In the case of Zehrina 
pendula, hundreds of determinations made during the past ten years of the 
osmotic pressures of epidermal cells by the piasmolytic method, using various 
salts and sugars, give values which range between 4.0 and 4.5 atmospheres. 
It would appear, therefore, that in the case of Zehrina pendula the values as 
obtained by the piasmolytic method are not far from being the true values 
for the cells observed. It should be pointed out, however, that the pias- 
molytic values were obtained entirely from pigmented cells of the lower 
epidermis, and it is not improbable that the osmotic pressure of the chloro- 
phyllous cells is greater than that of the pigmented cells. Furthermore, 
the guard cells of the stomates, as pointed out by Iljin (6), may show a much 
higher osmotic pressure than the adjacent cells, the differences observed 
being as high as 80 atmospheres. In our laboratory, R. A. Wiggans has 
found by the piasmolytic method, differences not to exceed 7 atmospheres 
for Iresine and 6 atmospheres for Zehrina pendula. 
Another possible explanation to account for the great difference is that 
by the cryoscopic method the sap is expressed from the conducting tissue 
as well, and it is not improbable that the concentration of solutes in the 
conducting system may be in excess of that of the mesophyll cells. This 
idea is supported by the evidence of Davis, Daish, and Sawyer (i), who 
found that the ratio of hexoses to sucrose is higher in the midrib and stalks 
than in the remainder of the leaf, and also that total sugars are actually 
higher. 
