i7, e Trelease: Salt Requirements of Wheat Plants 555 
Severe magnesium injury, pronounced root modifications, and 
the phenomenon resembling “stooling” were all clearly confined 
to solutions in which the ratio of magnesium to calcium lay 
between the limits 1.65 and 13.43; that is, in which the amount 
of magnesium sulphate was relatively high as compared with 
the amount of calcium nitrate. Of the remaining solutions, 
those in which the Mg/Ca-ratio value lay between the limits 
0.81 and 3.64 showed slight magnesium injury. This form of 
injury in general was confined to the range of the ratio values 
from 0.81 to 13.43, and entire freedom from injury was shown 
in the cultures which had ratio values within the very narrow 
range from 0.21 to 0.81. 
Shive found that when his three-salt solution had an osmotic 
value of 1.75 atmospheres the plants were free from magnesium 
injury with Mg/Ca- values of less than 1.5 ; and when the osmotic 
value was 4.00 atmospheres this limit occurred with the ratio 
value 2.2. From Tottingham’s data it appears that no injury 
occurred with ratio values below 0.40, when the total osmotic 
value was 2.50 atmospheres; or below 0.28, when that value 
was approximately 8.00 atmospheres. This limiting value of the 
ratio Mg/Ca is thus seen to vary considerably according to the 
kinds of salts used, the salt proportions, and the total concen- 
tration of the solution. It may be added, however, that no 
case has been observed in the experimental studies here con- 
sidered in which freedom from magnesium injury occurred with 
a ratio having a higher value than 2.90, except with solutions 
of very low total concentration where, Shive and Tottingham 
agree, none of this injury occurs at all with any value of this 
ratio. 
Dry weights . — Inspection of the tetrahedral diagram of fig. 
1 shows that the highest dry yield of tops was obtained in 
culture T2R4C2, having volume-molecular partial concentrations 
of the four salts as follows: 0.0067 M potassium chloride, 
0.0138 M monopotassium phosphate, 0.0047 M calcium nitrate, 
and 0.0081 M magnesium sulphate. Lowest dry yield of tops 
(60 per cent of the highest) occurred in culture T1R1C1, having 
volume-molecular partial concentrations of the salts as follows : 
0.0033 M potassium chloride; 0.0033 M monopotassium phos- 
phate ; 0.0023 M calcium nitrate ; and 0.0309 M magnesium Sul- 
phate. The areas of low yields of tops occur in all triangles 
along the left-hand margins, corresponding to regions charac- 
