434 BOTANICAL GAZETTE [NOVEMBER 
The other potatoes were placed in a dark box and inclosed in an 
ice chest the temperature of which was 2-5° C. At different 
intervals specimens were taken from each collection, washed care- 
fully, peeled so that considerable cortex was left with the central 
part of the potato, and then they were broken down with a glass 
scraper in a porcelain dish and the sap expressed from the potato 
pulp. This was tested in the Beckmann apparatus, the directions 
given by HAMBURGER in Osmotischer Druch und I onenlehre being 
followed. 
Procedure and results © 
The accompanying graphs indicate the readings at stated inter- 
vals. Graph 1 (fig. 1) shows the gradual rise of osmotic pressure in 
the ice box Burbank 
pin’ sa sy mw mf sn soe su o_o =t—2~| potatoes between the 
es beginning and the 
be close of the experi- 
ae ment, October 31, 
He 1911, to January 23; 
LAN {i 1912. At the latter 
u 









yaaa date the pressure of 
ma EE the potato sap meas- 
/ \ : ured in atmospheres 
we CURVES oF osmoTiC PRESSURE was 14.051. Ty ¢ 
oa pressure measure- 
SaeRing PiSep Fiterea = Boom Md 
+ 2 the room potatoes In 
this experiment 
Fic, 1 ber 
ceased on Decem 
5, When the osmotic pressure, measured in atmospheres, reached 
7.4. During the progress of this work it seemed possible that 
filtration might prove interesting, consequently a set of tests Wt 
the filtered sap paralleled those made with the unfiltered sap- In 
most cases the readings of the unfiltered were higher than those of 
the filtered sap. 
The notable diminution in the pressure curve for December 5 
was very difficult to account for at the time the reading Ws 










ae 
i 















