riz BOTANICAL GAZETTE | AUGUST 
exclude air. If the admission of air is unavoidable invert the appar- 
atus and allow it to collect under the funnel. 
After the plant has been allowed to stand for a few minutes obser- 
vations may be begun. 
Remove the cylinder of water at C and allow a bubble of air, 5™" 
long, to enter the tube, then replace. Note the exact time necessary 
for the bubble of air to traverse the calibrated portion of the tube as 
well as its separate divisions. When the bubble passes the calibrated 
portion of the tube open the stopcock and drive the bubble beyond the 
zero-point. The observation can then be repeated. 
The conditions of transpiration of the shoot may be controlled by 
means of a bell glass and by regulation of the temperature, light, etc. 
The collection of small air bubbles in the tube which are picked up by 
the moving bubble may be avoided by the use of freshly boiled water 
allowed to cool in a closed vessel. The increase in the size of the 
moving bubble would, of course, be a source of error. ‘The use of a 
horizontal calibrated tube avoids sources of error found in vertical 
tubes. 
For demonstration in the lecture room replace the cylinder of 
water with one of aniline dye after a bubble has been allowed to enter 
the tube, and use the end of the colored column as an indicator. A 
time piece and thermometer may be conveniently placed upon the 
support as shown in the illustration. 
The various precautions necessary to secure normal eanecudeie 
data must, of course, be observed. Thus, branches in which negative 
pressure exists must be allowed to stand in water several hours 
previous to use. This is illustrated by the following experience. A 
leafy shoot of fuchsia in which a negative pressure existed was cut off 
under water at 12:45 P.M. and fastened to the apparatus at 1 P.M. 
After a few minutes the following observations were made: 
1:27 P.M. Indicator bubble at o™, Temp. at0°C. 
1:50 ry e 2 ‘* 300 “21.0 
2205 os as ” “500 “21.0 
27.94 ” a ‘* 600 “21.0 
Readjusted 
ae 4 ag a 3 oh fe) ‘F208 
2228 i: a by *. 166 “20.7 
2:40 = a Y * 200 2S 
2 
. 57 ae se ae se 300 ae 20.0 
