[Vor. 7 
10 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
acid; and when given below they represent cc. of 0.1 n sodium 
hydroxide. Thus Ap/10 indicates the addition of 10 cc. of 
0.1 n NaOH to the A solution with peas. For the purpose of this 
paper we have considered molar phosphoric acid to be the sum of 
the values derived by titration against normal alkali, using as 
indicators both phenolphthalein and methyl orange. 
I have attempted to control or counterbalance, in a measure, 
the addition of phosphorus when added as phosphoric acid by 
the introduction in one or two cultures of an amount of phos- 
phorus in the form of the secondary salt equivalent to the acid 
added. At the same time, however, the addition of this salt 
necessarily shifts slightly the hydrogen ion concentration toward 
neutrality. The addition of sodium in the form of the alkali 
was in a measure controlled by adding as sodium sulphate an 
amount of this cation which is equal to that supplied in 10 cc. 
of alkali. As the work has progressed some other variations 
have been employed, notably the addition of solid calcium car- 
bonate (1 gm. per culture, 240 ec.) to solution B, likewise of solid 
aluminium hydroxide, and of kaolin, the addition of phosphate 
in part as the primary salt and in part as the secondary salt, 
also variations in the form and amount of phosphate employed, 
and significant changes in the proportions of solution B. Modi- 
fications of the culture indices denoting such changes will be 
explained as these are introduced. 
EXPERIMENTAL DATA 
There are given in tables 1, 11, and 111 the results of the first 
tests conducted with wheat, corn, and peas respectively, using 
solutions A and B. In consulting these tables it is to be remem- 
bered that the “culture indices" are intended to afford briefly all 
necessary faets concerning the constitution of the solution, and 
an explanation of these has been made on p. 9, so far as the 
unmodified solutions and those containing additions of acid and 
alkali are concerned. In the tables referred to above, K/10 and 
K/20 represent respectively additions of K,HPO, to balance the 
amounts of phosphorie acid added in cultures with similar 
numerals; and Na indicates the addition of sodium sulphate to 
equal the quantity of gram atoms of Na in 10 ec. of n/10 NaOH. 
The wheat cultures were grown 17 days, the corn 21, and the 
