Tue Errect of MANGANESE COMPOUNDS ON SOILS AND PLANTS 395 
was considered as zero. When phenolphthalin was used as an indicator 
similar results were obtained, altho some trouble was experienced with 
these solutions because of the carbon dioxide content. 
The bluing of gum guaiac was also used as an indication of the oxidizing 
power of the roots. The reagent, which was poured on the surface of the 
cultures, followed the path of the roots where it was oxidized. The 
objection has been raised that due consideration was not given to the 
oxidizing power of the manganese sulfate. It was found that a solution 
of gum guaiac is oxidized immediately by a solution of manganese sulfate 
containing approximately 10,000 parts per million of manganese. A 
solution of 1000 parts per million, however, gave only a slight bluing 
after three hours. Immediate bluing was obtained by the roots of plants 
grown in the presence of 10 parts per million of manganese in the form 
of the sulfate, while the bluing by the roots of the check plants was slow 
and not so intense. 
Effect of manganese sulfate on soil bacteria 
Numerous investigators have reported that the activity of the lower 
forms of plant life is increased by the presence of manganese salts. In 
order to test this point, cultures were set up to determine the effect of 
manganese sulfate on the ammonification of dried blood and the nitrifica- 
tion of ammonium sulfate in soil. These cultures were prepared from a 
fresh stock of Dunkirk silt loam, which had been passed thru a two- 
millimeter sieve and which contained 12 per cent (dry basis) of water. 
Portions of the soil each weighing 112 grams were placed in eight-ounce 
salt-mouth bottles. When properly treated the cultures were placed on 
the laboratory desk and covered with a moist pad, made of cheesecloth 
and cotton, to prevent the evaporation of water. It was found that in 
this way a large number of cultures could be kept at a constant moisture 
content with the expenditure of a minimum amount of labor. The 
cultures were run in quadruplicate and were incubated at room temper- 
ature. Two days after the cultures were set up, the soil in each bottle 
was stirred so as to insure uniformity in the distribution of the salts added. 
At the end of the incubation period, the soil in each bottle was stirred 
with 475 cubic centimeters of distilled water for three minutes and then 
allowed to settle for twenty minutes, and the supernatant liquid was 
filtered thru a Pasteur-Chamberlain filter. Aliquot portions of the filtrate 
were then analyzed for ammonia and nitrates. The ammonia was deter- 
