9 
c, 1 Broivn: Growth of Eloclea 
Table II. — Growth of Elodea with arid without addition of COi. 
No. of experiment. 
Growth in cm with ' 
addition of CO2. ' 
Growth in cm without 
addition of CO2. ; 
Tap water. 
Tap water 
and soil. 
Tap water. 
i Tap water 
1 and soil. 
1.8 
1.6 
3.4 
1.7 
1.6 
3.2 
Dead. 
Dead. 
Dead. 
1 Dead. 
1 Total 
The results show little difference between the plants in the jars 
with and without soil, but the beneficial effect of the addition of 
CO 2 is very evident. 
In order to test, more accurately, the effect of the addition of 
CO 2 , two series of three-liter jars were prepared on February 
sixth. One jar in each series contained tap water diluted with 
an equal volume of distilled water; another only tap water; 
while the bottom of the third was covered with a layer of burnt 
soil and the jar filled with tap water. Ten plants, 10 cm in 
length and without roots, were then placed in each jar. CO,, 
from a generator, was passed through the water in the jars of 
one series for from five to ten minutes several times each day. 
The water was not changed during the experiment. The average 
growth of the ten plants in each jar, for periods of three and ten 
days, is given in Table III. 
Table III. — Groivth of Elodea with and without addition of CO2. 
(All figures are averages for 10 plants.) 
Time. 
Tap water | 
diluted 100 iTap water, 
per cent. | 
Tap water 
and soil. 
With addition of CO2 — 
Days. 
Cm. ( 
Cm. 
Cm. 
3 
0.9 
1.0 
i 0.8 
10 
3.2 
3.3 
2.8 
Without addition of CO2— 
3 
0.3 i 
0.3 
1 0.25 
10 
0.3 
0.3 
I 0.25 
These results show comparatively little difference between the 
plants in either series but a decided advantage in favor of those 
in the jars to which CO 2 had been added. At the end of the 
third day these had made about three times as much growth as 
