i7, 6 Trelease: Salt Requirements of Wheat Plants 541 
other planes are represented by triangles. The seven triangles 
in fig. 1 (numbered T1 to T7) represent as many horizontal 
planes passed through the tetrahedron and all the points upon 
any one triangle denote solutions having the same partial con- 
centration of potassium chloride. Similarly, the position of a 
point upon any one of the triangles indicates the osmotic pro- 
portions of the other three salts in the corresponding solution. 
The lines are so drawn that their intersections represent the 
salt proportions actually employed. It will be seen that there 
are twenty -eight solutions (triangle 1) that are characterized by 
having 0.1 of their total osmotic concentration due to potas- 
sium chloride, while there is but one solution (triangle 7) in 
which 0.7 is due to this salt. 41 Each solution will be designated 
by a triple number, the first part denoting the triangle (as T2), 
the second the horizontal row of intersections in that triangle 
(as R3), and the third representing the number of the inter- 
section in the row, counted from left to right (as C2). The 
solution just described is thus named T2R3C2, and the four 
salts contribute, respectively, the following proportions of the 
total concentration : potassium chloride, 0.2 ; monopotassium 
phosphate, 0.3; calcium nitrate, 0.2; and magnesium sulphate, 
0.3. The triangle number gives the number of tenths due to 
potassium chloride, the row number gives the number of tenths 
due to monopotassium phosphate, and the culture number gives 
the number of tenths due to calcium nitrate. The number of 
tenths of the total concentration due to the fourth salt (mag- 
nesium sulphate) is found by subtracting from 10 the sum of 
the numbers appearing in the designation of the solution. 
The actual chemical composition of each of the eighty-four 
solutions in series I is given in Table 1, in terms of the volume- 
molecular partial concentrations of the four salts. The first 
column of this table gives the culture numbers of the solutions 
just described, and the last three columns give the three cation- 
ratio values of each solution, which will be referred to later. 
To obtain these concentration values, it was necessary to cal- 
culate the volume-molecular partial concentrations of each salt 
that would produce 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, and 0.7 of 1.60 
atmospheres of osmotic pressure at 25° C. The values thus 
obtained are given in Table 2. 
41 For a more detailed discussion of the interpretation of this kind of 
diagram, Tottingham’s paper may be referred to. 
