1915] OSTERHOUT—ADDITIVE EFFECTS 229 
solution (diluted to 200 cc.) produces exactly the same effect, 50 cc. 
of solution A (diluted to 200 cc.) produces a different effect from 
50 cc. of B (diluted to 200 cc.). 
Let us now consider an antagonism curve obtained by growing 
plants in a culture solution made by mixing the two solutions, A 
and B, so as to make too cc. ‘of mixture, 
C.c. which is then diluted to 200 cc. 
The result of growing plants in such mix- 
tures may be expressed by a curve, as shown 
in fig. 2. In this figure the ordinates repre- 
150- sent growth, while the abscissas represent 
the number of cc. of solution A, or of 
solution B, taken (and diluted to 200 cc.) 
to make up the culture solution. Thus, 
A 60, B 40 means that 60 cc. of solution A 
100- was mixed with gocc. of solution B and 
sufficient water added 
to make 200 cc. 
To measure the 
amount of antago- 
nism at any point on 
50, this curve according 
0 30 60 M.M. 
Fic. 1.—Curves showing growth in various dilutions of two solutions of salts, A 
and i the abscissas qos growth; the ordinates represent the number of cc. of 
which are mixed with water to form 200 cc. of the culture solution in 
Heide A plants were pains the two salt solutions are equally toxic at certain con- 
centrations but not at others; the curve C is drawn by taking points half-way between 
A and B (measured chan Sf it serves aS a basis of comparison in computing 
additive effects. 
to the method outlined in previous papers,? we must first 
determine the additive effect. To ascertain this at any point, 
2 Bor. Gaz. 58:178, 272. 1914. 
