17, 6 Trelease: Salt Requirements of Wheat Plants 599 
by magnesium, is essential for the greatest dry weight of tops.** 
The problem thus suggested will not be discussed here, but it 
is important to consider what salt proportions may be expected 
to give the highest top yields without magnesium injury. The 
results of the first two series indicate that either solution 
T38R3C3 or T2R34C34 may fulfill these requirements. An 
examination of Shive’s data makes it appear that his solution 
R7C2, having an osmotic value of 1.75 atmospheres, should pro- 
duce highest top yield without magnesium injury. The various 
characteristics of the solutions just mentioned are brought 
together for comparison in Table 17. 
From a study of the osmotic properties of the nutrient solu- 
tion, as distinguished from its chemical properties, it was found 
that the optimum concentration for the yield of tops corresponded 
to an osmotic pressure of about 1.60 atmospheres, at 25° C., when 
the salt proportions were those of solution T2R4C2. The indi- 
cations are that for these salt proportions the optimum 
concentration may be somewhat higher than 1.60 atmospheres, 
rather than lower. From the results of the present study this 
statement is true also for a three-salt mixture which would be 
designated on Shive’s composition triangles as R5C24 and which, 
therefore, very closely resembles his best three-salt solution 
for wheat tops. 
The optimum concentration was found to be markedly higher 
for two other sets of salt proportions of the four-salt solution 
used in this study. The osmotic value was 3.50 atmospheres for 
solution T1R1C1 and 4.50 atmospheres for solution T7R1C1. 
These two solutions had salt proportions that gave relatively 
low top yields, and the yields from their optimal concen- 
trations were very much lower than those obtained from 
the optimal concentration of solution T2R4C2, which had the 
best proportions for top yield. It may be tentatively concluded 
that solution T2R4C2 with an osmotic value of 1.60 atmospheres, 
or perhaps a little higher, is about the absolute optimum for these 
four salts, for the frequency of solution renewal and for the 
plants employed, and for the general greenhouse conditions and 
length of growing period of the present study. 
It seems worth while to lay stress upon some of the prominent 
considerations that must be constantly borne in mind in trying 
® Free, E. E., and Trelease, S. F., The effects of certain mineral poisons 
on young wheat plants in three-salt nutrient solutions, Johns Hopkins Cir- 
cular N. S. No. 3 (March, 1917) 199-201. 
