304 
JAMES GEERE DICKSON 
were reanalyzed for the elements related to the work and calculations 
were based upon these analyses. 
The chemicals were dried at constant temperature until anhydrous 
or until a definite amount of water remained and then reweighed; 
distilled water was then added to give the required salt concentration 
for the stock solutions. In the preparation of the salts it was necessary 
to make extensive determinations of water content and composition 
at the various temperatures used in those cases in which no published 
data for the compound in question could be found. Whenever the 
methods of other investigators were used they were carefully checked 
in all cases before being adopted as standards for drying the salts. 
Calcium nitrate, potassium nitrate, monopotassium phosphate 
(Tottingham, 1914), sodium chloride, sodium nitrate, and potassium 
chloride were dried at 150° C, and weighed as anhydrous. Mag- 
nesium sulphate was dried at 160° and treated as containing one 
molecule of water (Tottingham, 1914). Sodium sulphate was dried 
at 200° and weighed as anhydrous. Calcium chloride was dried at 
200° and treated as containing 0.2 percent water by weight (Weber, 
1882). Magnesium nitrate was dried over commercial sulphuric acid 
(sp. gr. 1.84) and treated as containing two molecules of water. Mono- 
sodium phosphate was dried at 100° and weighed as anhydrous. 
Ferric chloride was weighed without previous drying and considered 
as containing six molecules of water. 
The modified Knop's solution which was used in all the work, 
as shown in table i, was of one tenth the concentration described 
above, and contained, therefore, 0.15 grams total salts per liter instead 
of 1.5 grams. Previous work has shown that, when wheat and oats 
are watered during the growing season with the nutrient solution at 
the higher concentration, the accumulation of salts exerts an inhibiting 
influence upon their growth. 
2.5 cc. of a ilf/ioo solution of ferric chloride were added to every 
liter of culture solution. 
The complete cultural series consisted of the "normal" solution, 
that is, of Knop's solution modified as shown in columns three and four 
of table I, and five further modified culture solutions in each of which 
one of the elements magnesium, calcium, potassium, phosphorus, 
and nitrogen was reduced to one tenth of the quantity present in the 
"normal" solution (tables 2 and 3). A quantity of each solution 
sufl^cient for the demands of the entire growing season was made up 
