Feb., 1922] 
ARNDT THE GROWTH OF FIELD CORN 
53 
Salt Requirements of Representative Agricultural Plants, a solution of one 
half the molecular concentration of R2S3 was well within the range necessary 
for the optimum growth of corn. A solution was used whose partial 
volume-molecular proportions were as follows: KH2PO4, 0.0024 ^5 Ca- 
(N03)2, 0.0036 M; MgS04, 0.0035 M. This solution probably had an 
osmotic pressure close to 0.5 atmosphere. 
In this solution it was impossible to prevent precipitation when the 
various salts were added. Consequently, the results of the experiments 
in which this solution was used are not strictly comparable with those in 
which solution '*H" was used. They are comparable when considered in 
relation to the effect of the composition of the nutrient solution upon the 
tolerance of acidity by corn. Because of this precipitation, a renewal of 
the solutions at small intervals would have had little effect on the amount of 
the salt in the solution. To economize time, the ferrous sulphate solutions 
of 0.001 A^and higher were changed twice a week; the others were changed 
once a week. 
Sand Cultures 
Solution '*H" was used in all sand cultures. The method of McCall 
('16) as modified by Johnson ('20) was used for changing the solution. 
The cultures containing ferrous sulphate were renewed every day; the 
others, every third day. The sand did not contain sufficient iron for the 
optimum growth of corn. Ferric phosphate was added to the solution as 
in the solution cultures. The ferric phosphate was added to the ferrous- 
sulphate cultures every third day, as most of the phosphate probably was 
held in the sand and was not withdrawn when the solutions were renewed. 
After 2000 g. of sand was placed in each pot, it was thoroughly washed 
a second time by drawing 3 liters of distilled water through it. The sand 
used for the acid cultures was treated for 48 hours with strong sulphuric 
acid and then thoroughly washed until the water withdrawn was neutral. 
These sand cultures were not covered with a wax seal. This was thought 
desirable in order to simulate soil conditions as far as possible. A wax 
seal would have reduced the aeration and induced conditions in the soil 
which would undoubtedly have increased the toxicity of the ferrous salts. 
In order to secure some idea of the relative amount of water lost through 
evaporation and transpiration, a pot without plants was placed in the 
series and treated as the others. The amount lost through transpiration 
was calculated by deducting the loss from this pot from the total loss of 
the other cultures. The error introduced by this method of determining the 
transpiration should be small, as the loss through evaporation was relatively 
small in comparison to the total water loss. 
The writer wishes to express to Dr. J. W. Harshberger his sincere appre- 
ciation of the interest and assistance which made possible the experiments, 
and to acknowledge his indebtedness to Dr. G. N. Hoffer of the Office of 
