OSMOTIC PRESSURES IN THE POTATO PLANT 
pressure in the sap of the periphery of the leaflets as compared to that near 
the midribs. The leaflets were cut as shown in Fig. i. Both old and young 
plants were used. Errors were introduced into the determination by the 
evaporation from the cut surfaces, but the readings were at least compara- 
tive. The sap obtained from the periphery of the leaflets from both young 
and old plants recorded a higher osmotic pressure than the sap secured from 
the region of the midrib. The high percentage of sucrose in the peripheral 
portions must also be noted. Similar trials were made on August 19, 
when even greater preponderances in peripheral osmotic pressures and 
sucrose contents were evidenced. Similar cryoscopic results were recorded 
on August 22, although the sugar determinations were not made. 
Fig. I. Potato leaflet, percentage of water in the periphery, near the 
midrib, and in the midrib. 
Sunflower leaves were similarly tested on August 19, and showed reverse 
results both as to pressure and sucrose percentages. 
A determination was made on August 20 of the depressions of the saps 
secured from the tips and from the butts of the leaflets. The tips showed 
over an atmosphere greater pressure than the butts, due to higher sucrose 
percentages. 
The water content of the leaflets was determined by cutting them up into 
small pieces as indicated in Fig. 2, weighing, drying at 100° C. for 4 to 5 
hours and reweighing. While the leaflet periphery contained sap of a 
higher osmotic pressure than that in the midrib (2), the leaflet really is 
much more succulent along the midrib and toward the base than it is toward 
its outside. The leaflet, in spite of the higher peripheral osmotic pressure, 
