6 
The Philippine Journal of Science 
1913 
0.034 per cent of CO„. The jars used in most of the experi- 
ments reported in this paper contained three liters of water, 
which, under ordinary conditions, would absorb from the air less 
than 1.02 cc of CO,. The rapidity with which this amount 
might be used by the plants in the experiment was determined 
in the following manner. Ten plants, 10 cm in length, were 
placed in a three liter jar. The number and length of the plants 
was the same as that usually employed in the experiments, while 
the bulk was much less than would ordinarily occur in nature in 
the same amount of water. On a bright day, CO, from a gener- 
ator was passed through the water in the jar for ten minutes. 
After allowing an interval of fifteen minutes for the plants to 
become adjusted, the rate of absorption of CO, by the plants 
was calculated by measuring the amount of oxygen given off 
from the cut ends of the stems. This was found to be 1 cc in 
two minutes for the ten plants. Since this figure does not take 
into account all of the oxygen given off by the leaves and was 
probably not a maximum rate, it would seem that the plants 
could easily use up 1 cc of CO, in two minutes in the process 
of photosynthesis. This would mean that all of the COj which 
the water would absorb from the air could be used by the plants 
in two minutes ; and that, if the air were the only source of CO^, 
the process of photosynthesis would be retarded unless the 
amount of CO,, necessary to establish an equilibrium between 
the air and water, were to diffuse into the water every two 
minutes. This would, of course, be a much more rapid rate than 
could possibly occur. 
Since the bulk of the plants, in the experiment just discussed, 
was much less than would ordinarily occur in nature in the same 
amount of water, it would seem that the process of photosyn- 
thesis, and probably also growth, would be accelerated if CO, 
were added to the water from some other source besides the air. 
In nature such CO, might come from animals living in the water 
and from the decomposition of organic matter in the soil. If 
water, which did not contain living organisms, was standing over 
soil, which gave off CO, in any considerable quantity, the layer 
of water in contact with the soil would take up some or all of 
this CO, and would contain a higher percentage of it than water 
into which CO, diffused only from the air. The CO, would then 
diffuse from this lower layer to the upper ones where it would 
tend to diffuse into the air until the water contained a smaller 
