10 
The Philippine Journal of Science 
1913 
those in the other jars. By this time the plants in the jars, 
through which CO, had not been passed, had ceased growing, 
while the others were still making a good healthy growth. This 
would seem to show that under the conditions of this experiment 
the amount of CO, which diffused into the water from the air 
was not sufficient for the growth of the plants. Since the stock 
cultures were kept in jars through which CO, was passed, and 
all of the plants were making a healthy growth at the time that 
the experiment was started, it would also seem that a deficiency 
of CO 2 affects the growth of the plants very quickly. 
On February eighteenth, two series were prepared which 
were similar to the last except that a jar, the bottom of which 
was covered with a layer of good soil, was added to each series. 
As in the last experiment ten plants, 10 cm long and without 
roots were placed in each jar. CO^, from a generator, was then 
passed through the water in the jars of one series for from five 
to ten minutes several times each day. The average growth of 
the plants in each jar, for periods of three and ten days, is given 
in Table IV. 
Table IV. — Growth of Elodea with and without addition of CO2 to water. 
(All figures are averages for 10 plants.) 
r 
! 
Time, 
Tap water 
diluted 100 
per cent. 
Tap water. 
Tap water 
and burnt 
soil. 
Tap water 
and soil 
containing 
organic 
matter. 
Growth with addition of CO2— 
Days. 
Cm. 
Cm. 
Cm. 
Cm. 
3 
1.0 
1.1 
0.9 
1.3 
10 
3.2 
3.5 
3.0 
4.2 
Growth without addition of CO2. 
3 
0.3 
0.35 
0. 25 
0.5 
10 
0.3 
0.35 
0.25 
1.6 
At the end of three days the plants in all of the jars to which 
CO 2 had not been added, except those in the one with a layer of 
good soil, had ceased growing ; while at the same time the plants 
in the corresponding jars, through which it had been passed, had 
made about three times as much growth as these, and continued 
to grow vigorously during the course of the experiment. 
These results are similar to those obtained in the last experiment. 
The greatest growth was made by the plants in the jar, the bot- 
