8 The Philippine Journal of Science 
191S 
own 
jar, the bottom of which was covered with a layer of soil, the 
plants in this jar had made an average growth of 2.3 cm, while 
those in the jar with the bag of soil had grown only 1.2 cm. 
At the end of twenty days those in the jar, with a layer of soil 
in the bottom, had made an average growth of 5.2 cm, were 
well rooted and had a vigorous appearance. At the same time 
two of the plants in the jar with the bag of soil were dead 
while the other eight were in an unhealthy condition and had 
on the average, only 2.1 cm. The differences between 
the plants in the three jars could not have been caused by the 
roots because these differences were apparent before any of 
them were formed. This confirms the conclusions drawn from 
the preliminary experiments. The results must have been due 
to some change produced in the water, by the soil. It did not 
seem probable that the differences in the plants in the jars, with 
soil, could have been connected with the amount of salts in solu- 
tion, for the water in the jar, with a bag of soil, was probably 
saturated for that soil. Later experiments will show that tap 
water contains a sufficient quantity of salts to keep ten plants 
alive for twenty days, and for them to make a much greater 
growth than any of the plants in this series. Differences in 
the amount of CO^ present seemed to be more probable explana- 
tion. The soil used contained considerable organic matter and 
gave off CO.. The layer of soil, in the bottom of the jar, afforded 
a larger surface for the entrance of O and the giving off of CO^ 
and besides contained more soil than the bag in the other jar. 
The jar with tap water and no soil received only the amount 
of CO2 which diffused from the air into the water. 
To test the effect of adding CO^ to water in which the stems 
were growing, the eight plants, in the jar with the bag of soil, 
which were still alive on the twenty-fifth of January were dis- 
tributed two in each of four jars. Two of the jars contained 
only tap water, while the bottoms of the other two were covered 
with a layer of soil from which all organic matter had been 
removed by burning. CO^, from a generator, was then passed 
through the water of one jar containing only tap water and 
one with the layer of soil. This was done by running a glass 
tube to the bottom of the jar and allowing the gas to pass 
through the tube. 
At the end of ten days the plants, in the jars to which CO 
had not been added, were dead; while the others had, despit^ 
their unhealthy condition, made a more vigorous growth than 
in the previous experiment. Measurements of the growth of the 
plants are given in Table II, 
