17, 6 Trelease: Salt Requirements of Wheat Plants 597 
Tottingham’s and in Shive’s studies, and has been termed “mag- 
nesium injury” by Tottingham. The plants giving lowest yields 
in all three studies exhibited this form of injury, and all three 
studies support the conclusion that the occurrence and sever- 
ity of this injury is related to the ionic ratio of magnesium 
to calcium in the culture solution. This is the only case brought 
out by any of these three studies (Tottingham’s, Shive’s, and 
the present one) in which a clear relation may be regarded as 
demonstrated between the value of an ionic ratio and the de- 
velopment of the plant. The occurrence of this injury was, in 
general, not altered by the presence in the solution of potassium 
chloride, except perhaps with very high proportions of that salt. 
In the present study the greenness of the foliage was roughly 
proportional] to the severity of the injury, the color being darkest 
green in the most severely injured plants. Only two sets of 
salt proportions producing this injury were tested with total 
concentrations other than the one generally employed in this 
study; but these agreed in showing that both severity of injury 
and intensity of color increased with increase in the osmotic 
value of the solution. The plants in the most dilute solution 
(0.50 atmosphere) were markedly chlorotic. 
The occurrence of magnesium injury is apparently limited, 
as has been stated, by the value of the Mg/Ca-ratio. With solu- 
tions having an osmotic value of 1.60 atmospheres this injury is 
to be looked for, under the conditions of the present study, when 
the value of the ratio Mg/Ca is greater than 1.70. Also, the 
plants may be expected to be without this injury when this ratio 
value is below 0.80. Since neither Shive nor Tottingham de- 
tected any injured plants in their series of lowest concentrations, 
and since in series IV of the present study injury was found to 
increase with increase in concentration, it may be expected that 
these approximate limits will differ with difference in the total 
concentration. : 
The solution giving highest top yields with a total osmotic 
value of 1.60 atmospheres (T2R4C2) contained the four salts in 
the following partial volume-molecular concentrations: 0.0047 
M calcium nitrate, 0.0138 M monopotassium phosphate, 0.0081 
M magnesium sulphate, and 0.0067 M potassium chloride. This 
solution is not very different from what would be obtained by 
diluting Shive’s best solution for wheat to an osmotic value of 
1.28 atmospheres, and then adding sufficient potassium chloride 
to give a partial volume-molecular concentration of this salt 
of 0,0067 M. Ghive’s best solution contains the other three 
