1920] 
DUGGAR—H-ION CONCENTRATION AND NUTRIENT SOLUTIONS 5 
The solution of Livingston and Tottingham, here designated 
solution C, possesses the following partial volume-molecular 
concentrations: KNO, 0.0216; Ca(H;PO,), 0.0026; and 
MgSO., 0.0150. Iron is supplied as in the case of solution A, 
the modified Shive solution. It is assumed that this solution 
has approximately the osmotie value of solution A above 
described. 
The methods of experimentation employed were in large 
measure those which I have described elsewhere (11). “Well- 
seasoned" tumblers holding somewhat more than 250 cc. were 
used as culture vessels in all cases, the process of seasoning new 
tumblers consisting of filling them with a weak acid-dichromate 
cleaning solution and then steaming in the autoclave for one 
hour at 15 pounds pressure. Subsequently the tumblers were 
thoroughly washed and rinsed with distilled water. The dis- 
tilled water used here and in preparing the solutions was in some 
series from a Stokes still and in other series double distilled from 
glass. After transferring, with pipette or burette, the required 
amounts of each constituent stock solution to the tumbler, the 
volume was made up to 240 cc. In those cases in which Canada 
field peas were used the tumblers were covered with heavy paraf- 
fined paper made fast by rubber bands. Small holes were 
punched in the paper and the radicles of the seedlings inserted. 
Additional support for the growing seedlings was afforded by 
means of wire supports. In the case of both wheat and corn 
the seedlings were inserted into notches or holes in a paraffined 
cork, the latter just fitting the mouth of the tumbler. All 
cultures contained ten plants, and duplicate tumblers were 
arranged in every case not otherwise indicated. 
In most of the experiments here reported Merck’s blue label 
chemicals have been employed, but under the conditions existing 
at the time it was not possible to be entirely uniform in this 
regard, and other standard reagents were used where necessary. 
No recrystallization or other purification method was applied 
to any salt employed in the culture solutions. Stock solutions 
of convenient concentration were prepared, and so far as prac- 
ticable every factor and procedure was made uniform, or com- 
parable, throughout. It soon became evident that the content 
of free phosphoric acid in the dihydrogen potassium phosphate 
