Apr., 1922] GERICKE — BALANCE IN NUTRIENT SOLUTIONS 18I 
possibilities respecting order of rotation. All cultures were rinsed with 
distilled water before being transferred to another solution. The cultures 
were in contact with the solutions belonging to a type for an equal length 
of time. The experiment was planned to supply the plants with the 
nutrients in piecemeal fashion, and not together at one time, as was the 
case with those grown in complete nutrient solutions. 
It was conceived as very probable' that some of the nutrient salts would 
be found better suited for plant growth than others, because of differences 
in properties due to the composition of the salts. The results of the tests 
are given in table i. 
Table i , Dry Weight in Grams of Wheat Seedlings Grown Four Weeks in Six Different Types 
of Single Salt Solutions and in Complete Nutrient Solutions 
(Averages of 24 cultures of 5 plants per culture for each type and for the six types of complete 
nutrient solutions) 
Type 
Type 
Type 
Type 
Type 
Type 
Complete Solutions 
I 
II 
III 
IV 
VI 
(All Types) 
•51 
.61 
•59 
.40 
.96 
•43 
1.02 
The table shows that the salts of type V, that is, KNO3, MgHP04, 
and CaS04, when used singly gave far better yields than did those of any 
other type. They were approximately as good as those of any type of 
complete nutrient solution tested, in which the total osmotic value was 
divided equally among three salts. As to the order of change of cultures 
from one solution to another, this appeared to be of only minor importance, 
and hence no data on this matter need be given ; but the kind of salt used 
in making the changes was of great importance. While the pn values of 
the single-salt solutions employed were not the same in all cases, nevertheless 
they were within the range appropriate to good plant growth in complete 
solutions, and it is, therefore, assumed that the differences in dry weight 
produced were due to other causes than reaction of solution. Because 
only one salt was used at a time, it appears that the cause must be in the 
way in which two essential ions are paired, that is by the composition of 
the salt. Observations of the tests and the interpretation of the data given 
showed that when wheat seedlings absorb nitrates, potassium must be 
available; the absence of any one of the other essential elements for a period 
of at least forty-eight hours for these young plants apparently was not 
injurious. Furthermore, seedlings which were exposed for twenty-four 
hours in a solution that contained equal concentrations of only magnesium 
and phosphate ions (MgHP04) sustained no apparent harmful effects (to 
either top or roots), but if they were placed for a similar length of time in 
equally dilute or diluter solutions of MgS04 or Mg(N03)2, they sustained 
decided injury. MgHP04 seems to be a very good salt to supply the plants 
with magnesium and phosphate. Calcium-sulphate solution proved to be 
