372 McLean . — Field Studies of the Carbon 
per cent, of the photosynthesis gain. His work makes the dry weight 
observations of doubtful value for precise comparisons, but as here used 
they have some interest for comparison with results by gas analysis. For 
this purpose two full-grown, dark green leaves were selected from healthy 
canes of about the same size, and of the same variety and age, growing side 
by side. These were removed from the plants at 5 a.m. on May 16. One 
side of each leaf was stripped from the midrib, their green weights and 
areas were determined, and then they were dried in a double-walled 
oven at ioo° C. The remaining half-leaves, attached to the midribs, were 
placed with their cut ends in rain-water in glass phials, and one half-leaf 
was introduced into the test cylinder of the apparatus for determining 
the carbon dioxide absorption. The other was exposed beside the first, 
but left uncovered. 
Table I. 
Titration results from tests of carbon dioxide absorption by a detached half- . 
leaf of sugar-cane on May 14, 1918. Area of half- leaf, 194*9 sq. cm. 
(25*07 c.c. Ba(OH) 2 used in the apparatus was equivalent in concentra- 
tion to 2o*io c.c. of 0*0432 normal HC 1 ). 
Hour of 
Amounts of acid in c.c. 
Concentra- 
removal required to neutralize 
from ap- 25.07 c.c. of Ba(OH) 2 from 
Wash bottles of 
tion of HCl 
used in 
Weather conditions. 
paratus. 
Pettenkofer 
tubes of 
titration. 
Test. 
Control. 
Test. 
Control. 
A.M. 
17*60 
17*55 
19* 8 5 
19*85 
0.0432 
5. 35 a.m., quite cloudy. 
7 * 3 ° 
i 7* 6 5 
1 7*55 
19*85 
19 * 9 ° 
,» 
6.45-7*45, bright sun. 
17-60 
17*55 
19*85 
19*85 
33 
19*70 
1 8*oo 
19*90 
19*85 
7.45-8.20, dull. 
9.30 
19.70 
1 8*oo 
19.90 
19*90 
3 3 
8.20-9.20, bright sun. 
19.70 
18.00 
19.90 
19.90 
” 
1 
[ 19*75 
j8*io 
19.90 
19.90 
33 
9.20-1 1, dull. 
ii.30 
I 9 * 7 ° 
18.05 
I 9 * 9 ° 
19.90 
33 
1 1-1 1.35, bright sun. 
1 
l 19*75 
i8*io 
19*90 
19.90 
33 
P.M. 
19*50 
i8*io 
19*95 
19.90 
33 
11.35-n.48, dull. 
I.30 
19*50 
i8*io 
I 9*95 
19*95 
33 
i 9 * 5 o 
18.15 
19*95 
19*95 
3 3 
1 1,48-2.45, bright sun. 
t 
f i 9 * 7 o 
18.20 
19*95 
19*95 
„ 
3 - 3 ° i 
I 9 ' 7 ° 
18.15 
19*95 
19*95 
3 3 
2.45-3, cloudy. 
1 
l i 9*75 
18*20 
19*95 
* 9*95 
33 
3-3*35, bright sun. 
i 
f 2I *°5 
19*35 
21*25 
21*25 
OO4O5 
3*35-4*45, dull. 
5-30 
21*05 
: 9*35 
21.25 
21.20 
33 
1 
l 21*05 
19*40 
21.25 
21.25 
33 
4.45-6, bright sun one- 
half of the time. 
6.30 \ 
f 20*30 
20*25 
21*25 
21.25 
3 3 
20*30 
20*25 
21*30 
21.25 
33 
1 
l 20*30 
20*25 
21*25 
21.30 
3 3 
6.30, light quite dim. 
