368 Ale Lean . — Field Studies of the Carbon 
The investigation here reported was undertaken to devise a method of 
measuring the carbon dioxide absorption of field crops in situ under 
conditions as little modified as possible. The study was carried out during 
class work in plant physiology at the College of Agriculture, Los Banos, 
Philippine Islands. 1 
Method. 
The leaves to be studied were enclosed in a glass tube, 61 cm. long and 
3.5 cm. in diameter (see PL XVIII, Fig. 1). The lower end of the tube 
enclosing the bases of the leaves was left open. The other end was fitted 
with a one-hole rubber stopper, through which was passed a 6 mm. glass tube 
connecting the large tube enclosing the leaf with the carbon dioxide extracting 
apparatus. Air was passed through this apparatus, which consisted of the 
following parts arranged in the order named : a series of three wash bottles, 
each containing 60 c.c. of sulphuric acid, a Pettenkofer tube containing 300 c.c. 
of barium hydroxide of known concentration (0*035 normal, more or less), 
a wash bottle containing an equal volume of the same solution, and a glass 
stop-cock to regulate the flow of air. The air then passed into an aspirator 
consisting of a large metal tank of about 380 litres capacity, so regulated by 
the glass stop-cock as to give a flow of nearly 19 litres of air per hour 
through the apparatus. A similar set of apparatus, connected to the same 
aspirator tank, but without a leaf in the open tube, was run beside it 
as a control. 
The series of sulphuric acid bottles was introduced to equalize the 
moisture content £>f the air in the test and control apparatus, and also 
to prevent undue dilution of the barium hydroxide solutions in the 
Pettenkofer tubes. The air was introduced into the Pettenkofer tubes 
through glass tubes drawn out to 1 mm. top diameter. These regulated the 
size of the bubbles passing through the Pettenkofers so that they were about 
one centimetre long when they were flattened out along the tops of the 
tubes. Practically all of the carbon dioxide was removed from the air 
passing through the Pettenkofers. This was proved by the tests of the 
contents of the barium hydroxide wash bottles, which always showed a very 
small reduction in the alkalinity of the solution, and this reduction was 
found to be produced by the transfer of the solution from the bottle of 
stock solution to the wash bottle, and thence to the flask used for settling the 
solution after decanting. Furthermore the concentration of barium hy- 
droxide in the wash bottles after each test was found to be identical for the 
test and the control apparatus, thus showing that the carbon dioxide content 
of the air leaving the apparatus, if there was any, was the same for test and 
control. The difference between the amounts of carbon dioxide absorbed 
1 The measurements here reported were made by Messrs. A. Mangonon, T. Ventura, and 
G. Yap, working under my direction and supervision. 
