^"i- c. 1 Brotvn: Growth of Elodca 15 
growth would be retarded more frequently by a scarcity of CO 
than by a deficiency of nutrient salts. ' 
VALUE OF ROOTED CONDITION 
The different rates of growth, shown by the plants in the 
solutions of nutrient salt of various strengths, were all apparent 
before roots were formed on any of the plants. It is evident, 
therefore, that different concentrations of nutrient salts as well 
as of CO2 may affect growth independently of the roots. It 
remains to be seen, however, whether the rooted condition is 
of value to the plant. 
An attempt to test this point was made in the following 
manner. Three ten-liter battery jars were filled with tap water 
and the bottom of each covered with a layer of good soil con- 
taining organic matter. Ten plants 10 cm in length were then 
placed in each jar. Those in the first were held against the 
soil by small glass rods and soon became rooted. The plants in 
the other jars were left floating near the surface of the water. 
The roots of the plants in the second jar were allowed to grow 
down into the water while those of the plants in the third were 
removed as soon as formed. The stubs left on the plants 
collapsed very quickly so that it is not likely that they serv^ed 
as absorbing organs. The cut ends of all the plants were plugged 
with parafine. No CO. was passed through the water in any of 
the jars. 
Very early in the experiment a flourishing growth of algae 
covered the soil in the jars containing the floating plants. At 
the same time the jar containing the rooted plants appeared to 
be free from algae. Several attempts were made to grow algae 
in this jar by transferring to it rather large quantities from the 
jars with floating plants. In every case the algae failed to make 
any appreciable growth and soon disappeared. The most reason- 
able explanation of this seemed to be that the CO, from the soil 
could be used by the algae when the plants of Elodea were floating 
near the surface while it would be largely taken from the water, 
by the latter, when they were anchored to the soil. The fact 
that these algae did not do well in ordinary tap water, except 
when CO2 was passed through it, is in harmony with this con- 
clusion; see Brown.8 From what has been said it would seem 
that the rooted plants of Elodea should receive more COo and 
make a better growth than the floating ones even though the 
roots were of no advantage in absorbing nutrient salts. 
'Contr. U. S. Nat, Herb, 13 (1911) 323-341. 
