+ 
viii, c. 1 Brown: Growth of Elodea 3 
sure exerted by the weight of the water above the lower end. 
Barnes * suggests that the heating of the leaves may create the 
conditions necessary for the circulation of water in aquatics. It 
would appear that the three factors mentioned above are suffi- 
cient to explain the movements of the water in Elodea and that 
the movement is therefore a necessary consequence of the 
physical construction of the plant. 
That water should ascend in a plant under such conditions 
certainly does not justify the conclusion that the movement is 
of advantage to the plant by causing a condensation of nutrient 
salts or that roots are of advantage as absorbing organs. It may 
be noted here that proof is lacking for the theory that trans- 
piration causes a condensation of these salts in terrestrial plants. 
Pond ^ grew a number of submerged plants including Elodea 
canadensis, rooted in good soil; anchored over the same soil; 
rooted in sand; and floating over sand. The plants rooted in 
soil grew very much better than those in any of the other three 
conditions. Pond states that the six plants studied by him, 
''are dependent upon their rooting in the soil for optimum growth, 
and can not survive a single season if denied a substratum of 
soil." This writer did not reach any definite conclusion as to 
the explanation of this fact but seemed to incline to the view 
that the greater growth of the rooted plants was connected with 
the absorption of nutrient material by the roots. 
. Brown ^ observed that the submerged aquatics of Lake Ellis 
were distributed according to the nature of the soil substratum, 
Elodea canadensis and Sphagnum occurring on muddy soil con- 
taining large quantities of organic matter, while MyHophyllum 
and Eriocaidon compressum grew on a coarse sandy soil. This 
writer suggested that the distribution of the plants might be 
due to different amounts of CO.. given off by the two soils. 
The experiments, reported in this paper were carried on in 
the green house of the Botanical Department of the Johns Hop- 
kins University during the winter and spring of 1910. The 
writer wishes to express his thanks to Prof. B. E. Livingston 
for valuable suggestions and criticisms and for placing every 
possible convenience at his disposal. 
* Barnes, C. R. BoL Gaz. 49 (1910) 77. 
'Kept. U. S. Comm. Fish and Fisheries 29 (1905) 483-526. 
• Brown, W. H. The Plant Life of Ellis, Great, Little, and Long Lakes 
in North Carolina. Contr. U. S. Nat. Herb. 13 (1911) 323-341. 
