1909} MERWIN AND LYON—SAP PRESSURE IN THE BIRCH 457 
curve B.) Therefore, 32°° is close to the amount supplied by the roots 
and therefore about 34°° came from expansion within the tree. The 
experiment of two days before showed the amount of gas in this tree 
to be 45 to 80°°, an amount which, by expansion, is sufficient to 
account for the flow here considered. 
20 
‘ 5:25 6:05 6:45 7:25 AM 
\ it 
> 
% 
‘ 
Sects 
oe ore 
; a oe 
™S 
\ : 
SS 3 
x => —— 2 B 
——+$_ —__-— ot Re ae A 
a 
= 
9 min, 10 20 30 40 50 
Fic. 5 —A, pressure ay the base of a white birch, April 16, 1906, while flow was taking place from a hole 
ff up; B, rate of flow in drops per minute of the hole above A; the continuation of curves A and B are D 
a in another tree the decline of pressure while sap was flowing freely is shown by C 
EXPERIMENT 3.—To determine the amount of expansion of 
saturated cell-wall substance of birch wood. 
Across the grain of a white birch plank thin shavings were taken. 
From these the air was entirely expelled under the receiver of an air 
pump. The shavings were then transferred to a 100°° pycnometer. 
The pycnometer was filled up with freshly boiled, distilled water, and 
weighed at 6° C., and again at 32° C. The weight of the pycnometer 
