17, 6 Trelease: Salt Requirements of Wheat Plants 591 
without chloride, can be significantly improved for the produc- 
tion of top yield under these general conditions by altering the 
total concentration. As has been mentioned, it is possible that 
the yield might have been a little higher had the total concen- 
tration been slightly increased. But it is safe to regard a con- 
centration value of 1.60 or 1.75 atmospheres as optimum for 
both sets of salt proportions, under the aérial conditions fur- 
nished by the greenhouse used in this study, and with the plants 
and frequency of solution renewal employed. 
The two other four-salt proportions included in this series 
(TIR1C1 and T7R1C1), both of which gave very low top yields 
with a total concentration value of 1.60 atmospheres in series 
I and II, here show their highest top yields with a concentration 
value of 3.50 atmospheres and 4.50 atmospheres, respectively. 
As in the case just discussed, concentrations below and above the 
optimum show much lower yields. The two graphs are seen to 
be nearly parallel throughout. Their form differs from that 
of the other two graphs of this series, not only in position of 
the maximum but also in the fact that they are nearly sym- 
_ metrical about the maximum. Both are rather flat-topped. 
While root yields (fig. 10) agree in a general way with top 
yields as related to the total concentration of the nutrient solu- 
tion, some rather marked differences occur in other respects. 
It will be noticed that both the heights of the graphs, indicat- 
ing actual yields, and the forms of the graphs, showing the rela- 
tion of changes in concentration to changes in yield, differ for 
the four sets of salt proportions tested. The graph for the 
T2R4C2 cultures shows that maximum root yields were obtained 
with a concentration of 1.60 atmospheres, from which it appears 
that this solution cannot be significantly improved for root pro- 
duction by changing its total concentration from 1.60 atmos- 
pheres. It will be observed, however, that solution R5C23, 
which had no chloride and resembled Shive’s best solution for 
tops, gave a slightly higher root yield with a concentration of 
2.50 atmospheres than with one of 1.60 atmospheres. The dif- 
ference, however, is small. With the two concentrations higher 
than 4.50 atmospheres root yields were significantly higher with 
the solution containing the chloride (T2R4C2) than with 
the one that lacked it (R5C24). Apparently, high total con- 
centrations are less injurious to roots in the presence of the 
chloride than in its absence. The graph for culture T7R1C1 
(having 0.7 of its concentration due to potassium chloride) is 
175542——5 \ 
