1912] Lipman : Bacteria in Soils of Arid Begions 7 



not only in the upper layers of the soil, but in the lower layers 

 where an actual examination of the root-systems of plants shows 

 a large development of fibrous or feeding roots. A study, there- 

 fore, of the ammonifying powers of the different layers of soil, 

 or, rather, of the microorganie flora which they contain, is of 

 practical moment, since it is bound to throw light on the soluble 

 nitrogen supply for roots in the greater depths of soil and 

 indicate what practical measures may be taken toward siLstain- 

 ing and encouraging the growth and activities of the organisms 

 responsible for that soluble nitrogen supply. Since, therefore, 

 we assume ammonia production to be the first great step recog- 

 nized by our analytical methods in the transformation of soil 

 nitrogen, I have first determined the ammonifying powers at 

 various depths of soils, which may be considered typical of well- 

 defined areas and conditions in the arid region. 



For this purpose there were inoculated into sterile 50 c.c. por- 

 tions of 1 per cent peptone solution, 5 grams of soil from every 

 foot from the surface down to the last depth taken, as above 

 described. After four days incubation at about 28 degrees 

 centigrade, the cultures were washed into copper distilling flasks, 

 sufficient distilled water added, as well as a slight excess of 

 magnesia, and distilled. The distillate was caught in standard 

 tenth normal hydrochloric acid, the excess of w^hich was titrated 

 with standard tenth normal ammonia. Table I gives the results 

 of determinations of the ammonifying power of the soils chosen, 

 as above described. The ammonifying power of only one soil, 

 namely No. 6, is not given, for the reason that the soil column 

 had inadvertently become contaminated before we were ready 

 to use it. 



The numbers of the soils refer to corresponding numbers 

 under the descriptions given above, and the amounts of ammonia 

 produced, as given in the table, represent milligrams of nitrogen 

 as ammonia. 



The data given in table I prove very clearly two facts. First, 

 that in the typical deep and normal soils of the arid region, the 

 activities and the distribution of the ammonifying flora seem to 

 run parallel with the texture, the chemical composition, and the 

 root-development in these soils. Second, that in the absence of 



