AMERICAN 
JOURNAL OF BOTANY 
Vol. Ill February, 1916 No. 2 
THE EXCHANGE OF IONS BETWEEN THE ROOTS OF 
LUPIN US ALB US AND CULTURE SOLUTIONS 
CONTAINING THREE NUTRIENT SALTS^ 
Rodney H. True and Harley Harris Bartlett 
Elsewhere in this Journal the authors have given data on root 
absorption from solutions containing a single nutrient salt,^ and also 
from mixed solutions of two salts.^ It may be recalled that the roots 
of young seedlings of Lupinus alhus actively absorb calcium salts. 
Magnesium salts are absorbed to a less extent and only from solutions 
which are so weak that toxic action does not occur. Potassium and 
sodium stand in marked contrast to calcium and magnesium. Their 
solutions greatly resemble distilled water in that the roots placed 
in them either excrete electrolytes regardless of the concentration or 
else effect a minimal absorption. The somewhat different effect of 
different salts of the same base indicates that absorption is influenced 
not only by the cation but also by the anion. 
The addition of even a very small amount of a calcium salt to 
a solution of a magnesium salt increases absorption to a remark- 
able degree. The same effect is also observed when calcium is 
added to a potassium salt. In mixtures of two nutrient nitrates there 
usually seems to be a ratio which is more favorable to absorption 
than any other. In certain cases where the total salt concentration 
was 240 N X io~^ the absorption from mixtures was found to be 
greater than from either constituent salt alone. In weaker solutions 
^ Published by permission of the Secretary of Agriculture. 
2 True, R. H., and Bartlett, H. H., The Exchange of Ions between the Roots 
of Lupinus alhus and Culture Solutions Containing One Nutrient Salt. Amer. 
Journ. Bot. 2: 255-278. 1915. 
3 True, R. H., and Bartlett, H. H., The Exchange of Ions between the Roots 
of Lupinus alhus and Culture Solutions Containing Two Nutrient Salts. Amer. 
Journ. Bot. 2: 311-31. 1915. 
[The Journal for January (3: 1-46) was issued Feb. 5, 1916 J 
47 
