2 University of California Publications in Apririilturdl Sciences | Vol. 1 



in depth, and to obtain a knowledge of the chemical constitu- 

 tion and the texture of the soils by makina: systematic chemical 

 and mechanical analyses of all the samples thus collected. The 

 information thus obtained in the several years in which the soil- 

 columns were studied by Ililgard and Loughridge and the large 

 number of types of soils considered, along with the most striking 

 circumstance of the depths to which plant root-systems of the 

 arid regions penetrated, led Hilgard to believe that the striking 

 chemical and mechanical differences between the soils of the arid 

 and humid regions, as well as the diiiPerences in the development 

 of the root-systems in these regions, respectively, might find 

 a parallel also in a difference between the bacterial flora at 

 various depths in the soil. It was this belief on Hilgard 's part 

 and his valuation thereof as being of exceeding scientific interest 

 as well as practical value, that led to the association with him 

 something over three years ago of the writer, and it was then 

 that I undertook, among other biological problems in soils, a 

 study of the nitrogen-transforming and nitrogen-fixing bacteria 

 in the different layers of soils in the arid region. This study, 

 while it has progressed considerably, is still in the first stage 

 of its development and the complete results thereof are intended 

 ultimately to be combined with the mechanical and chemical 

 analyses of these soils in a comprehensive report on the whole 

 work. For the purposes of this paper, it is sufficient to give a 

 resume of some of the important results obtained in these inves- 

 tigations with an account of the methods employed in the work, 

 so that it may serve as a preliminary communication on the sub- 

 ject and bring out certain striking facts with reference to the 

 distribution of bacteria in California soils. 



:\[ETHODS EMPLOYED IX THESE INVESTIGATIONS 



One of the most difficult problems in connection with these 

 investigations was to find a method for the collection of soil 

 samples at the several depths -which would fairly represent the 

 actual conditions which obtain there, so far as the bacterial 

 flora are concerned. Our first attempts in this direction were 

 made with an auger of the type manufactured by Iwan Brothers 

 at South Bend. Indiana, bv means of which we tried, through 



