2(1 University of Culifoniia Publications in Agricultural Sciences [Vol. 1 



CONCLUSIONS 



Investigations of the distribution and activities of bacteria in 

 soils of the arid region show : 



1. That samples of soil for studying the flora of each layer 

 of soil can best be obtained from a hole twelve feet in depth 

 Avith at least one vertical wall, the latter when sterilized being 

 sampled. 



2. That tin tubes ten inches long and about one inch in 

 diameter closed at one end and cotton-stoppered are best for 

 collecting the samples. 



3. That the solution method for studying the soils, despite 

 its many drawbacks, is the most feasible one to employ. 



-i. That soils of the arid region at all depths studied show 

 ammonifying powers which, however, are generally most 

 vigorous in the first six or eight feet. In one case ammouifica- 

 tion was noted in soil from a depth of fifteen feet, or adjoining 

 the water-table. 



5. That nitrification is found commonly down to a depth of 

 five to six feet in soils of the arid region. In one case soil from 

 the eight-foot depth showed a vigorous nitrifying power. 



6. That nitrogen fixation tlii'ough .Vzotobatcer does not go 

 on l)elow two feet in the soil usually, but has been found in 

 some soils at three feet and in one soil down to four feet. Many 

 soils in the arid region, otherwise favorably constituted, do not 

 contain Azotobacter organisms. 



7. That from the point of view of annnonification and nitri- 

 fication soils in the arid region differ markedly from those in 

 the humid region when the lower layers of soil are considered. 

 The difference is not marked as regards nitrogen fixation. 



8. The results above recorded help to explain the favorable 

 physical and chemical constitution of our soil and also the deep 

 rooting of plnnts so characteristic of the arid regions. 



Transmitted April 8, 1D12. 



