406 BOTANICAL GAZETTE [MAY 
ammonifying flora than like the nitrifying flora with respect to 
moisture. This is also in harmony with other results from the - 
point of view of factors other than the soil moisture content, which 
one of us has obtained with respect to the behavior of these three 
groups of organisms. 
5. We feel, as did DEHERAIN in his work cited above, that 
changes in the physical constitution of a soil will seriously modify 
the points of maximum and minimum bacterial activity with a given 
moisture content. But the more exact determinations of available 
moisture in all soils as advocated by Brices will probably indicate 
but slight variations from the optimum and minimum moisture 
contents necessary for the activity of soil organisms as determined 
for the ammonifying and nitrifying flora by the investigators 
above named and for the nitrogen fixing flora by us. 
LABORATORY OF SoIL CHEMISTRY AND BACTERIOLOGY 
UNIVERSITY OF CALIFORNIA 
