A THREE-SALT NUTRIENT SOLUTION FOR PLANTS 
A method similar to that used by Tottingham was here employed, 
to give a series of solutions differing in the proportions of the three 
salts, but all having approximately the same total osmotic concentra- 
tion as measured by the lowering of the freezing point. ^ A trace of 
ferric phosphate was added to each solution. Each series contained 
36 different solutions, instead of the 84 necessitated by the four-salt 
solution used by Tottingham. The plants here used were wheat 
{Triticum vulgare) (from the same lot of seed as was used by Totting- 
ham) and buckwheat (Fagopyrum esculentum Moench.), and the seed- 
lings were germinated and mounted in a manner similar to that 
employed by the earlier writer. All the three-salt solutions used in 
this comparison, including that with Tottingham's best proportions 
for wheat tops and the one with the regular Knop proportions, had 
approximately the same total osmotic concentration, but this was 
much lower than the concentration employed by Tottingham. They 
had a diffusion tension of 1.75 atmospheres (as measured by the lower- 
ing of the freezing point), while Tottingham's corresponding series- 
showed 2.50 atmospheres. Both these concentrations lie within the: 
optimum range for wheat. Tottingham's best solution for tops and 
the regular Knop's solution were included in this series for purposes 
of comparison. The cultures lasted 24 days, with change of solution 
every three days, the containers holding 250 cc. 
The solution giving the best growth of wheat tops contained the 
three salts in the following volume-molecular partial concentrations: 
KH2PO4, .0180m.; Ca(N03)2, .0052m.; MgS04, .0150m. This showed 
an improvement over Knop's solution, of the same total osmotic 
concentration, of 27 percent, while Tottingham's best solution here 
showed a corresponding improvement of but 16 percent. In the 
solution yielding the greatest dry weight of buckwheat tops the volume- 
molecular partial concentrations of the three salts were: KH2PO4, 
.0144m.; Ca(N03)2, .0052m.; MgS04, .0200m. The improvement 
produced by this medium, in dry weight of buckwheat tops, over 
Knop's solution of the same total osmotic concentration, was 61 
percent. The increase shown by Tottingham's best solution was 
21 percent. The data here given represent averages from two series, 
one conducted in August and the other in October. The two corre- 
sponding series agreed, both for wheat and for buckwheat, in the 
4 Shive, J. W. The Freezing Points of Tottingham's Nutrient Solutions. PL 
World 17: 345-353- I9i5- 
