369 
Dioxide Absorption of Coco-nut Leaves . 
by the solutions in the Pettenkofer tubes at the end of any test period thus 
shows the difference in the carbon dioxide from a leaf and from the free air, 
i. e. the amount of carbon dioxide absorbed by the leaf from the air. 
Diffusion of carbon dioxide from the outside air into the open end of the 
tube could not greatly increase the amount supplied to the leaf in this case, 
since the rate of flow of air into the tube was many times more rapid than 
the calculated rate of diffusion. Thus carbon dioxide was drawn in bodily 
into the apparatus at the rate of 6-2 m. per hour, many times as fast as it 
could possibly diffuse into the tube from a concentration of 0-0003 parts by 
volume to 0-00015 parts. 
The conditions surrounding the leaves tested by this method may 
be summarized as follows : The air supplied to the outer end of the 
leaf had the same carbon dioxide content as the outside air. Since this 
air was moving through the tube at the rate of 6*2 metres per hour, it 
was constantly being renewed. The tip end of the leaf was supplied 
with air, the carbon dioxide content of which was never reduced by the 
activity of the leaf to as low as one-half of its original value in any of 
the tests of coco-nut or abaca leaves. Thus the carbon dioxide supply 
to the tested leaves was not reduced to very much less than normal. It 
was, however, seriously reduced for part of the time during some of the 
hours of the preliminary test of a sugar-cane leaf. The intensity of the 
light falling on the leaves was materially reduced by the glass tubes 
enclosing them. No measurements were made of the light intensity inside 
of the tubes. The effect of all of the modified conditions produced by the 
apparatus on the rate of carbon dioxide absorption may have been 
appreciable. 
Procedure with Field Apparatus. 
Each test was of either one or two hours’ duration. Since the pro- 
cedure was similar in all, and most of the tests were for two hours each, the 
latter only will be fully described. It was found during preliminary work 
in adjusting the apparatus that the rates of flow of air through the control 
and test apparatus could not be maintained exactly alike. The differences 
were due almost entirely to differences in the setting of the glass stop-cocks, 
which could not be adjusted precisely enough, and to the bubble tubes, 
which were not exactly alike. These also became somewhat coated with 
barium carbonate. This was removed at the end of each test by means ot 
hydrochloric acid, and the tubes were rinsed before replacing them. 
It is, of course, essential to the success of this method that the amount 
of air passing through the test and the control apparatus be measurably the 
same, since it is desired to compare the carbon dioxide content of equal 
volumes of air from the same general source, the one having subsequently 
been acted upon by a leaf, while the other was not thus modified. In order 
