The Philippine Journal of Science 
191S 
The object of the experiments was not to determine quantita- 
tively the optimum conditions for the growth of Elodea, but to 
find out the manner in which a soil would most likely affect the 
growth and distribution of such a plant and if possible to deter- 
mine the value of the rooted condition. 
MATERIAL AND METHODS 
The original stock of Elodea was obtained from Henry A. 
Dreer of Philadelphia under the name Anacharis canadensis 
var. gigantea. This plant is especially favorable for the study 
of growth as long unbranched stems, without roots, are easily 
obtained. All of the experiments were started with unbranched 
stems 10 cm in length. 
Stock cultures were kept in battery jars with and without a 
layer of soil in the bottom and in others through which CO 2 
was passed for from 5 to 10 minutes several times a day. The 
last method produced the best plants and so was used exclusively. 
The CO, was obtained from a generator and passed through a 
solution of NaHCOs to remove any trace of acid. Commercial 
CO,, put up in tanks, was found to be very detrimental to the 
growth of the plants. This was probably due to the presence 
of some poisonous gas. 
Since individual plants and stems of plants, of the same 
species, are known to vary in their rates of growth, it seemed 
advisable to determine this rate for all stems before using them 
in an experiment. This was done by taking a large number of 
stems, 10 cm long, unbranched and without roots, and placing 
them in jars, through which CO, was passed as in the stock 
cultures, care being taken that all of the plants received prac- 
tically the same amount of light. At the end of three to five days 
the increase in length was measured and a selection made of 
those showing approximately the same rate of growth. The 
plants were then cut down to 10 cm in length and employed in 
an experiment. The length of all plants was measured from 
the cut end to the tips of the longest leaves around the growing 
point. A single average example will illustrate the value of 
this method. On the first of April 178 plants 10 cm in length 
and similar in appearance were selected and treated as just 
described. Four days later the increase in length was measured 
in mm. The results are given in Table I. 
