1 68 
Redfern. — On the Absorption of Ions 
a maximum fairly early ; this absorption was followed by a definite 
excretion of ions, and this was succeeded by a period of intake, so that the 
absorption-curve exhibited .a series of maxima and minima. Pantanelli 
made a number of experiments to determine changes in the acidity or 
alkalinity of the culture solutions, and the results confirmed his former 
conclusions. 
Johnson ( 3 ) observed a slightly unequal absorption of ions in a series of 
experiments with beet, carrot, and maize (white field corn and sweet corn) 
in calcium chloride solutions. He found that more calcium was absorbed 
in proportion by dead tissue than by living tissue in the case of beet, carrot, 
and sweet corn. 
These results cannot be accepted without further confirmation, because 
neither Pantanelli nor Johnson took account of the magnitude of the bio- 
logical error arising from individual differences in the plants examined, and 
they give no indication whether the differences they record are within or 
without the limits of this error. 
How serious this source of error may be is well illustrated by some 
figures taken from the results of the present investigation. 
In one case the absorption of chloride by one member of a group of pea 
plants was 5-64 per cent., and by another member only 2*878 per cent., 
while the average for the group was 3*578 per cent., with a probable 
error of 0*506. 
A still more striking case of individual variation is taken from the 
results of a series of experiments with maize plants in which absorption of 
calcium by one individual was 5-291 per cent, and by another 30.23 per 
cent. ; the average of the group was 17*53 P er cent *, ; with a probable error 
of 2*7. 
Hoagland ( 2 ) questions the unequal absorption of ions from salts such 
as potassium chloride in solution ; in his experiment the nutrient solutions 
remained neutral, or, if acid or alkaline to begin with, they gradually became 
neutral after contact with plant roots. Analysis of sodium nitrate solutions 
showed that more nitrate than sodium was absorbed ; the bicarbonate was 
formed, so that the solution did not become alkaline. In the case of 
potassium chloride solutions the potassium and chloride were absorbed in 
equal proportions. 
In the present research it was considered advisable to limit the 
investigation in the first place to the absorption of a single salt by plants of 
one or two species, and to obtain sufficient data to enable the probable error 
of experiment to be calculated, rather than to attempt experiments with 
a wide range of salts and species, in which it would be impossible to obtain 
sufficient data with any one salt or species to indicate the degree of 
accuracy of the results. The salt selected was calcium chloride, and the 
species used were the edible pea and maize. 
