20 The Philippine Journal of Science 1913 
taking nutrient salts from the soil and organizing them into 
vegetable matter. "Upon the decay of the vegetable matter this 
food material is believed to pass into solution in the water. It 
should there nourish the plankton algae.'' Reighard and Pond 
ascribe Kofoid*s results to the fact that the vegetation with 
which he was dealing was largely Ceratophyllum, and therefore 
not rooted. 
The experiments with Elodea would seem to show that such 
a plant would compete with the plankton algae for both CO.. and 
nutrient salts and would therefore be very detrimental to their 
growth. This is in agreement with the results obtained from 
experiments with algae; see Brown ''; and with the conclusions 
reached by Kofoid. 
Summary 
Sufficient CO, to keep Elodea growing or even alive does not 
diffuse from the air into the water at Baltimore during the 
winter and spring months. 
The substratum may serve as an important source of CO,. 
Elodea is not dependent on its roots for the absorption of 
nutrient salts. 
A solution of eosin may rise in the vessels of a cut stem of 
Elodea at the rate of 4.2 cm a minute. This appears to be due 
to certain physical factors and does not show that the roots are 
of advantage as absorbing organs. 
The chief function of the roots seems to be that they anchor 
the plants to the substratum, which may be of great advantage 
to the plants when the soil contains organic matter and gives 
off CO,. This appears to explain the fact that plants rooted in 
a good soil grow better than those anchored over the same 
substratum. 
When CO, was not given off by the soil used in the experiments 
but was supplied from a generator the rooted and floating plants 
grew about equally well. When similar soils were used and no 
CO, supplied from a generator the floating plants grew better 
than the rooted ones. In this case the air was the chief source 
of CO2. 
It would seem that under natural conditions variations in the 
amount of CO, in the water are more likely to affect the growth 
of Elodea than variations in the percentage of nutrient salts in 
solution. 
"^Contr, V, S, Nat. Herb. 13 (1911) 323-341. 
