422 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9, 
The concentrations employed, as seen above, were 675 p. p.m., 1,350 
p. p.m., and 2,100 p. p.m. As ordinarily used, Pfeffer's solution contains 
1,500 p. p.m.; Knop's, 1,400 p. p.m.; Crone's, 2,000 p. p.m.; and Sachs', 
2,700 p. p.m. Solutions II and III as used in these experiments compare 
favorably in total salt concentration with those of Knop and Crone, re- 
spectively. 
Baker's analyzed CP. chemicals were employed. Each salt was dis- 
solved separately in a proportionate part of distilled water, and these com- 
ponents were mixed as needed; when a salt was difficultly soluble it was 
added in the form of a suspension. Ferrous sulphate was used as the source 
of iron, and was added directly to cultures when set up, and at each change 
of solution, at the rate of .002 gram per liter. 
The hydrogen-ion concentration of each solution was carefully checked 
by the colorimetric method each time solutions were prepared. In making 
up the standard solutions, Merck's specially prepared sodium phosphate and 
potassium phosphate, purified as specified by Sorensen, were used. The 
results were not compared finally with electrometric determinations, but 
by using overlapping indicators as suggested both by Prideau, and by 
Clarke and Lubbs, approximate accuracy was assumed. 
There was some variation in the hydrogen-ion concentration from time 
to time; this was attributed to the varying states of purity in the monobasic 
calcium and potassium phosphates, different lots of which had to be used 
as the work progressed. However, the pH value at the beginning of the 
first experiment was 6.47; and the range was never greater than from 5.59 
to 6.47. 
The plants grew well in these solutions and produced, as far as could be 
judged from appearances, healthy tops and roots over a period of 56 days, 
the longest duration of any set of experiments. 
Cultures were grown in the three solutions simultaneously. Mason 
fruit jars which have a capacity of about 1,000 cc. were employed as con- 
tainers. The screw-top type of jar was found to be the most practical 
kind for this work. It has the advantage that discs of paraffined manila 
paper may be inserted in place of the glass cap, which can then be made 
fast by screwing the metal band down tightly. The discs, held in this way, 
make a firm and stable support for the growing seedlings, and the operation 
entails very much less labor than the usual method of fastening the paper 
with rubber bands, or setting the seedlings in slit cork stoppers. Wire 
supports were made fast around the neck of the jar for support of the 
seedlings as they grew. Four cultures of each solution with four plants 
to a culture constituted a series. 
The seeds were germinated between moist blotting paper; when the 
radicles of seedlings to be used were about one inch in length, four holes 
were made through the paraffined discs with a clean, pointed glass rod, 
through which they were inserted into the solution. 
