378 E.- P. Deatrick 
due in part at least to a beneficial effect on ammonification and nitrifica~ 
tion.”” If, on the other hand, the salts “ restrict crop growth, that restric- 
tion may be due in part to a depression of bacterial activity.” 
Greaves (1916) has recently published his results. He states that with 
the possible exception of the chloride, all the manganese salts tested were 
strong stimulants to the ammonifying organisms of the soil. At maxi- 
mum stimulation, 25 per cent more ammonia accumulated than in the 
normal soil. 
Olaru (1915) states that the nitrogen-fixing power of bacteria from 
legumes is greatly increased by manganese. Gregario (1916) finds that 
mannitol bouillon containing 60 parts per million of manganese in the form 
of the chloride and inoculated with Bacillus radicicola fixes three times as 
much nitrogen as do the checks; a concentration of 200 parts per million 
retards the fixation. Furthermore, he finds that Clostridium pasteur- 
zanum, which normally is not a free fixer, becomes capable of fixing nitrogen 
in the presence of manganese. Similar results have been obtained with 
Azotobacter chroococcum. 
Summary 
Much of the evidence in the foregoing reports is contradictory. The 
results would be more intelligible if complete data regarding the experi- 
ments were given. The applications of manganese salts to soils have been 
made without any apparent consideration of the type of soil. Such 
factors as soil type, the presence of calcium, and the crop to be grown, 
are factors that determine the action of a given application. Large 
applications on a sandy loam are detrimental, while the same applications 
on a clay loam or on a soil high in calcium would in all probability be 
stimulative. 
The réle of calcium seems to be a complex one. If the manganese 
were stimulative in the soluble form, the addition of caictum would pre- 
cipitate the manganese and prevent the stimulation. If, on the other 
hand, the manganese were present in such concentration as to be toxic, 
the addition of calcium would be beneficial, not only by causing precipi- 
tation of the manganese but also by increasing the oxidizing power of 
the soil by such precipitation. 
Altho the evidence is in many respects inconclusive, the following 
statements seem to be justified by this review: 
1. Manganese is universally distributed in small quantities in soils and 
plants. 
