R. H. TRUE AND H. H. BARTLETT 
of salts by the roots is equalled by absorption. This equilibrium 
concentration is lower for calcium nitrate than for magnesium nitrate, 
and lower for an equimolecular mixture of the two than for either 
alone. In the latter case it is about a hundred-thousandth molecular. 
If the initial concentration of the culture solution is less than the 
equilibrium concentration, excretion from the roots predominates 
over absorption and brings about a net rise in the concentration. 
Conversely, if the concentration of the solution is initially above the 
equilibrium point, the roots absorb more salts than they excrete and 
the concentration becomes less. The results with peas showed, 
furthermore, that with a culture solution of appropriate concentration 
and composition, absorption may take place until the solution becomes 
almost as free of electrolytes as distilled water. In such a case, excre- 
tion is obviously a negligible factor, and the net change in concentra- 
tion of the solution must be ascribed to absorption alone. Absorption 
was found to be greatest in solutions containing calcium and mag- 
nesium nitrates in equimolecular proportions, but root growth was 
found to be equally good in any solution which did not contain less 
than one molecule of the calcium salt to nine of magnesium. In the 
more dilute solutions an even lower ratio of calcium to magnesium, 
I : 99, was found to completely overcome the deleterious effect exerted 
by magnesium alone. In other words absorption and growth appear 
to be more or less independent phenomena. 
The present paper extends the same line of investigation to other 
salts and to a different plant. Lupinus albus L. has been studied in a 
considerable range of concentrations of Ca(N03)2, CaS04, Mg(N03)2, 
MgS04, KNO3, K2SO4, KH2PO4, KCl and NaCl. Future articles 
will deal with the effect of various mixtures of these salts in pairs and 
in threes on the same plant. 
Methods 
The methods used were in general those described in our former 
article on peas (1. c). Carefully selected seeds of Lupinus albus were 
germinated in moist sphagnum and used when the primary root was 
about 50 mm. long. Four roots were used in each 500 c.c. culture. 
Readings were made daily until it became apparent from the appear- 
ance of the plants that they were approaching exhaustion. This stage 
was marked by the withering of the foliage leaves, the partial dying of 
the edges of the cotyledons, the frequent failure of the hypocotyls 
and by the loss of electrolytes from the roots. 
