268 
RODNEY H. TRUE 
ternal medium, since the sugar introduced equals the osmotic aggregate 
of the river water. This substitution seems to leave the water with 
harmful properties undiminished, although sugar in itself at this con- 
centration can hardly be called distinctly harmful. As was observed 
by Loeb (30) in his work on Gammarus, one finds here no marked 
improvement following the addition of the sugar. Indeed, the main 
features of the experiment strikingly resemble those of the check 
culture in which distilled water alone was used. Leaching was not 
hindered by the presence of the sugar but was perhaps somewhat 
accelerated. 
The addition of sodium chloride in quantity osmotically equal to 
the dissolved material in Potomac water exerts a marked beneficial 
action in the first 24 hours, but this seems to be lost during the second 
day. It is obvious that although the presence of this salt protects the 
roots to a certain degree, the protection is of a decidedly temporary 
nature. It also confirms the conclusion based on the action of the 
sugar solution that simple aggregate osmotic pressure is not the most 
important feature in the case. 
The addition of calcium chloride in osmotically equal quantity 
produces a strikingly different result. The growth rate assumes an 
apparently normal character throughout the course of the experiment, 
the peculiar "distilled water " action being absent. Since the Potomac 
water approaches in conductivity to a Mji ,000 KCl solution, giving a 
conductivity under the conditions of these experiments of about 
37 X io~4 reciprocal ohms as against 44.5 X lO""^ like units for 
ilf/1,000 KCl, it appears that the sugar solution behaves essentially 
like distilled water in showing an increasing conductivity on account 
of the extraction of electrolytes from roots. This assumes that the 
sugar is not significantly conductive under these conditions. It is 
also clear from the higher resistances that roots absorb electrolytes 
from the isotonic solutions of NaCl and CaCU in a way comparable 
with the absorption from Potomac water in the foregoing experiments 
(p. 266). In the case of these isotonic salt solutions, it is probable 
in the absence of considerable quantities of other electrolytes in the 
distilled water, that the absorption of NaCl and CaCU takes place. 
If such is the fact, the growth rate during the second day should reflect 
to a certain degree the effect of such absorption. If this assumption 
is justified, the absorption of NaCl is less favorable than the absorption 
of CaCU. On the other hand this difference in effect may be due to 
