270 
RODNEY H. TRUE 
distilled water should be used with caution in laboratory work as a 
check medium intended to present a norm of plant action. Potomac 
water certainly furnished more favorable and natural conditions for 
root growth in the plant here concerned than distilled water. It 
should be noted, however, in this connection that all plants are not 
equally sensitive to injury from this source, it having been shown by 
True and Bartlett (39) that Canada field peas make a fairly healthy 
growth in distilled water in spite of the fact that they lose a consider- 
able quantity of electrolytes to the outer medium. 
Summary of Results 
It appears probable from the results given in the course of this 
paper that the problem of injury by distilled water is not a simple one 
capable in all cases of a like explanation. In some cases, distilled 
water obtained from apparatus having copper surfaces exposed to 
contact with the water undoubtedly derives certain toxic properties 
from minute traces of copper. In other cases doubtless it is possible 
for other harmful impurities to find their way into the product, but 
after the action of all the impurities has been accounted for there still 
remains a residuum of harmful action due to no known type of im- 
purity. This mode of harmful action seems to be most marked in 
water which shows the highest resistance to the passage of the electric 
current. 
It is shown here that those samples of distilled water which show 
the highest resistance are in general more harmful to lupine roots than 
waters containing a large quantity of electrolytes. It is likewise 
shown that these same samples of water withdraw electrolytes from 
the tissues of the roots when they remain in the water. This leaching 
of electrolytes is shown to be the probable mechanism by means of 
which purer samples of distilled water exert their harmful action on 
the roots. This extraction by distilled water is regarded as but a 
special case of the general type of injury wrought on cells by un- 
balanced solutions whereby certain necessary constituents, undoubtedly 
in part inorganic, are dissociated from their proper attachments in 
the complicated chemical and physical mechanism of the living cell. 
The distilled water seems to withdraw material required for the main- 
tenance of the efficient action of the protoplasmic limiting membranes 
with the result that the permeability of the cells is increased, and a 
further dissociation of electrolytes from their points of combination 
