BE. P. I.—699. 
- ABSORPTION AND EXCRETION OF SALTS BY ROOTS, 
AS INFLUENCED BY CONCENTRATION AND COM- 
POSITION OF CULTURE SOLUTIONS. | 
I—CONCENTRATION RELATIONS OF DILUTE SOLUTIONS OF 
CALCIUM AND MAGNESIUM NITRATES TO PEA ROOTS. 
INTRODUCTION. 
In the course of work carried on several years ago by R. H. True 
in collaboration with Lyman J. Briggs, the change in salt concentra- 
tion of culture solutions in which seedlings of Lupinus albus were 
grown was followed during the growth of the plants by means of the 
method of electrical conductivity. The results (which have never 
been published) indicate that lupine roots, when grown in distilled 
water, excrete electrolytes which render the water so used a better 
medium than fresh distilled water for the growth of.a second set of 
seedlings. This clue has led to the use of the conductivity method 
in studying the influence of concentration on absorption and excretion 
of salts by roots of plants growing in dilute culture solutions. This 
bulletin reports the results of a series of experiments with field peas 
grown in solutions of calcium and of magnesium nitrates. It is to 
be followed by studies of other plants and of other solutions. Future 
work will be directed toward determining the chemical composition 
of the culture solutions after plants have grown in them, and also of 
the plant roots themselves, in the hope that the results may throw 
light upon the mechanism of permeability. The purely physical 
results already obtained, however, are of so much interest that they 
are presented at this time. 
CULTURE METHODS. 
On account of the great dilution of the solutions used (varying 
=a00 to son) it was necessary to make several modifica- 
tions of the usual water-culture technique. All cultures were made 
in liter beakers of Jena glass, boiled out with distilled water. In each 
beaker were placed 520 c. c. of distilled water. Two paraffined glass 
rods, crossing each other in the form of a letter X, of such length that 
their ends projected about 2 cm. from the water, served as supports 
for a cake of paraffin. This cake was made by pouring enough 
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