i7, 6 Trelease: Salt Requirements of Wheat Plants 539 
cubic centimeters, and the total loss for the entire period was 
415 centimeters. 
The general plan of this series is similar to that employed 
by Tottingham. Eighty-four solutions were made from four 
salts: potassium chloride, monopotassium phosphate, calcium 
nitrate, and magnesium sulphate. In each solution the four 
salts were so proportioned that the total concentration of each 
solution corresponded to 1.6 atmospheres of osmotic pressure 
at 25° C., and in the different solutions the proportion of each 
salt was varied by 0.1 of the total osmotic concentration of all 
salts. The lowest concentration of any salt was thus 0.1 of the 
total concentration and the greatest 0.7. AO of the possible dif- 
ferent proportions were used that could be produced by these 
variations. Thus, there were eighty-four different solutions in 
this series, all of which had approximately the same total os- 
motic concentration, but no two of which had the same set of 
salt proportions. This may be stated in another way by saying 
that all of the solutions were planned to have the same total 
number of particles (ions plus molecule's) per unit volume, but 
no two solutions the same proportions of the different kinds of 
particles. Besides the eighty-four solutions belonging in the 
series, Shive’s best three-salt solution for wheat and Totting- 
ham’s best four-salt solution for wheat were employed for the 
sake of comparison. 
If three salts had been employed instead of four, the compo- 
sitions of the solutions could have been represented graphically 
by means of points placed in an equilateral triangle, the points 
being so placed that the least concentration of one salt would 
have been along one side of the triangle and the greatest at the 
opposite angle. As four salts were used, a figure representing 
their various proportions assumes the form of a regular tetra- 
hedron. In this figure each face of the tetrahedron represents 
0.1 concentration of one salt and the opposite apex 0.7. Since 
seven proportions of each salt were employed, different concen- 
trations of the salt whose lowest concentration is represented 
by the base of the figure will fall in seven planes. For con- 
venience of graphical presentation the planes representing 
the different concentrations of potassium chloride have been 
plotted separately (fig. 1). Since only one culture that had the 
greatest concentration of potassium chloride was used, the plane 
which passes through the apex is represented by a point; the 
