4i8 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9. 
The full-strength solution employed by Stiles had a total salt concentra- 
tion of 1,830 p. p.m., while that used by Miss Brenchley contained 3,040 
p. p.m. In their investigations both workers grew plants in the full-strength 
solution and in three dilutions of the same (1/5, i/io, and 1/20 of the full 
strength). 
In making a critical examination of the results given in table 2 in con- 
nection with the dilutions employed, as well as in the light of the possible 
behavior of salts in very dilute solutions, the question arises as to whether 
these results are really significant in relation to a varying concentration as 
such, or whether or not they may be indications of a deficiency of one or 
more ions. In order that experiments may be conclusive on this point, ample 
precautions should be taken that the minimum requirements of essential 
salts are at hand throughout the duration of the experiment, otherwise we 
may have the lack of some salt as the limiting factor. Certain results to 
be reported later in this paper show that increasing the concentration alone 
in a solution, there being adequate nutrients present otherwise, will not 
give higher ratios of tops to roots than result in another solution with even 
lower concentration of total salts but of different chemical composition. 
As further evidence that concentration in itself is not a controlling factor, 
table 3, computed from table 15, page 187, of Tottingham's work (31), will 
be of interest. While the original paper in question does not give the ratios, 
it does give dry weights of tops and of roots from which the ratios have 
been calculated. It should be added that these results of Tottingham's 
are based mostly upon single cultures, and this fact should be considered 
in evaluating the data. 
Table 3 
Total Concentration of Salts in Solution (%) 
.05 
.10 
• IS 
.20 
• 25 
• 30 
•35 
.40 
^ ^. Tops 
Roots 
3.22 
3-13 
3.17 
2.58 
3.17 
3-03 
3-5 
3.11 
Total Concentration of Salts in Solution (%) 
•45 
■50 
• 55 
.60 
.65 
•70 
•75 
.80 
Tops 
Roots 
2.91 
2.84 
3.10 
3.00 
3.00 
3.03 
2.91 
3.10 
In the experiment upon which the table is based, the total concentration 
of the solution (a modified Knop's solution) varies, as will be noticed, from 
500 p. p.m. to 8,000 p. p.m., with no influence whatever, as the figures show, 
upon the ratios of top to root growth of the wheat plants employed. In 
another phase of his researches, Tottingham held the concentration con- 
