500 BOTANICAL GAZETTE [JUNE 
directly with amounts found by other workers for similar cultures run for 
various shorter periods, as four or six days. Such results are in no wise com- 
parable, since the initial rate of ammonification is normally low, but increases 
rapidly through the first six to ten days of incubation. 
In the determinations of nitrifying efficiency, SAckETT employed soils 
obtained from various parts of the United States as checks upon soils from 
different portions of the state. Here the Colorado soils were collected under 
states were taken by persons unfamiliar with bacteriological technique or with 
methods employed in soil sampling, and were subsequently shipped for long 
distances in widely varying types of containers. While the author deplores 
the failure to employ standard methods, he nevertheless draws rather sweeping 
conclusions as to the comparative ammonifying and nitrifying efficiencies of 
the two lots of soils, and asserts that the experiments demonstrate the presence 
in Colorado soils of a nitrifying flora distinct, either in species or in physiological 
efficiency, from that elsewhere found. It would seem to the reviewer that 
definite conclusions are not in order until concordant results have been obtained 
from repeated studies in which all possibility of variation in any significant 
factor has been eliminated. The necessity for caution is especially great here 
in view of the fact that the work of KELLERMAN and ALLEN” in Nevada, while 
showing the presence of large numbers of nitrifying and ammonifying bacteria, 
yields no indication of abnormally high rates of activity or of unusual activity 
of Azotobacter; while the more recent work of McBreTH and. SmitH, to be 
presently discussed, is wholly confirmatory of the results obtained by 
RMAN and ALLEN. 
At the Utah Experiment Station, the problem has been attacked by 
StEWart and his co-workers. In the course of their very thorough studies 
of the production and movement of nitrates in the soils of the Greenville 
farm's: *, 7 SrewarT and GREAVES reached the conclusion that bacterial action 
could not be responsible for the accumulation of any large quantities of nitrates 
at the surface of the soil, at least in irrigated areas, since nitrates are readily 
displaced into the deeper layers of the soil by the downward movement of 
oe water. In more than 30,000 determinations of nitric nitrogen, 
= 
I 
4 KELLERMAN, Kart F., and Aten, E. R., Bacteriological studies of the soils 
of the Truckee-Carson frigation project. Bull. U.S. Dept. Agric., Bur. Pl. Industry. 
no. 211. pp. 1-36. 1o1T. 
Ss STEWART, ROBERT, and Greaves, J. E., A study of the production and move- 
ment of nitric nitrogen in an irrigated soil. Bull. Utah Agric. Exper. Sta. no. 100. 
Pp. 67-96. 1909. 
%*—___. The movement of nitric nitrogen in soil and its relation to “nitrogen 
fixation,” Bull. Utah Agric. Exper. Sta. no. 114. pp. 181-194. IgII- 
———, The production and movement of nitric nitrogen in soil. Centralbl. 
Bakt. 347:115-147. 1912. 
