VIII, a 1 Broivn: Growth of Elodea 7 
percentage than the air. The result would be that the water, 
near the soil, would always contain more CO^ than that near the 
surface. In view of this it would seem that submerged plants 
might grow better anchored near the soil than floating near the 
surface, and that roots, by keeping the plants near the soil, 
might, in some cases, be an advantage to them. 
On the 14th of December, while carrying on experiments to 
determine the best way of keeping stock cultures, a large number 
of plants, which were for the most part without roots, were 
put in various kinds of jars, with and without a layer of soil 
in the bottom. At the end of three weeks it was found that 
all of the plants, in the jars without soil, were dead, while those 
in the jars with soil had made a good growth. There appeared, 
moreover, to be few if any more roots on the plants in the jars 
without soil than when the plants were first placed in them; 
while there was a vigorous growth of roots in the jars with soil. 
If the presence or absence of the rooted condition was the primary 
cause of the difference in the growth of the plants in the two 
cases, roots should have been formed in both, for they had to 
be produced in the second before the plants could become rooted. 
If would seem from this that the growth of the plants in the 
second case and the death in the first was not connected, prim- 
arily, with the presence or absence of the rooted condition ; but 
rather that the production of roots was an expression of the more 
vigorous condition of the plants. It would seem, moreover, that 
this vigorous condition must have been due to some change 
produced by the soil, in the water in which the stems of the 
plants were growing, 
To test this point more accurately a series of three-liter bat- 
tery jars was prepared on the fifth of January. The first con- 
tained only tap water. The second was filled with tap water to 
which was added a bag of cheese cloth containing about 200 cc 
of good soil; the idea being that the water would be a saturated 
solution of this soil, while the plants would not have a chance 
to become rooted. The bottom of the third jar was covered 
with a layer of the same soil as that used in the second. At the 
end of three days the plants in the jar with only tap water 
had made an average growth of 3 mm, but after this there was 
no further growth and in less than twenty days all of the plants 
were dead. During the twenty days of the experiment no roots 
were produced by the plants in either the jar with only tap 
water or the one with the bag of soil. At the end of ten days, 
when roots were just beginning to appear on the plants in the 
