Apr. 15. 1920 Effect of Solution Reaction on Germination and Growth 7 7 



In series B the reax;tiou was varied by adding to all cultures suflficient 

 H3PO4 to make the solution 0.0180 molecular and then NaOH in the 

 following volume-molecular concentrations : 



CS ^-0.5 



/o /3 20 e^s 30 



cc. Norma f NaOH per Liter 



JJ 



40 



2 34 3 



Culture /dumber 



Fig. 2. — A, graph showing the change in reaction obtained by electrometric titration in series B; B, graph 

 showing the change of reaction found after 4 days' growth of wheat seedlings in cultures of series B. 



The electrometric titration curve for this solution (fig. 2, A) was used 

 as a basis for determining the amounts of NaOH necessary to produce a 

 series of seven cultures ranging from about 2 Pq to about 8 Pg and 

 increasing in approximately equal steps of i Pg. The curv'e shows 

 a rather abrupt rise at a point representing the complete neutralization 

 of one hydrogen ion of the H3PO4 molecule. As will be shown later, the 

 solutions chosen upon the steep part of the cur\'e Avere less stable in 

 reaction than those chosen upon the more nearly horizontal parts of the 

 cur\^e. 



