50 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9 
The Present Investigation 
Solution cultures were used in the main part of this experimental work. 
These results were checked with sand cultures to determine to what extent 
the solution cultures might indicate the toxicity of these salts in the soil. 
In all cases the weight of the plants grown in the unmodified solution was 
taken as the control. The effect of the acid or salt is indicated as the per- 
centage of the weight of the plants grown in solutions containing them, 
as compared with the control culture. The weight in the control was 
taken as lOO percent. For the tops the green weight was used as a criterion 
of the relative growth, as this probably gives the best indication of the 
condition of the plants. Comparisons of the green and dry weights gave 
similar relative weights. As a criterion of the root development, the dry 
weight was used. The roots were placed in weighed test tubes and dried at 
100° C. for several days. 
The H-ion concentration for the solutions was determined by means 
of the Lubs and Clark (Clark, '20) series of indicators, using the buffer 
mixtures recommended by them. These were carefully prepared from re- 
crystallized salts. Standards were kept in Pyrex test tubes of 10 cc. 
capacity, the solutions to be tested were placed in similar test tubes, and 
the same concentration of the indicator was added to them. The H-ion 
concentration of the sand cultures at the time of the renewal of the solutions 
was determined by adding distilled water to bring the sand to 60 percent 
of its water-holding capacity; 50 cc. of the solution was drawn off by suction 
through a hose previously rinsed with distilled water; the new solution 
was then added, and the remaining 450 cc. was withdrawn. The pH value 
is reported for the 50 cc. and for the total 500 cc. drawn off. All solutions 
were clear. Consequently, turbidity did not interfere with the determina- 
tions. The pH values given to show the effect of the growth of the plants 
upon the reaction of the solution were determined just previously to the 
time of harvesting the plants. This was usually at the end of a warm, 
sunny period favorable for growth, as these conditions seemed to have an 
important effect on the results. 
The seed corn used in these experiments was Reid's Yellow Dent, a 
variety of yellow dent (or, according to Sturtevant ('94), Zea mays var. 
indentata), which was furnished by Dr. G. N. Hoffer. It gave practically 
100 percent germination. Very few grains showed any infection by parasitic 
organisms. The salts used were Raker "analyzed" chemicals. The 
ferric phosphate was prepared as recommended by the Committee of the 
National Research Council on Salt Requirements of Representative Agri- 
cultural Plants. All stock solutions of the salts and acids were made up 
as Njio solutions. These were made up fresh at least twice a week, except 
the ferrous sulphate which was made up immediately before it was used. 
The distilled water was prepared with a Barnstead still and was stored in 
glass containers. 
