144 



SOILS. 



first three fields were sent from the Kansas station for humus deter- 

 minations (courteously made by Dr. H. C. Myers), which gave the 

 following results : 



Field No. i 2.19% of Humus. 



" No. 2 3-07% " " 



" No. 3 1.85% " " 



While these humus-percentages are not directly proportional to the 

 bacterial content, a favoring effect of high humus-content is clearly 

 shown. The bacterial and the humus-content of these soils are sensibly, 

 even if not directly, correlated ; which might reasonably be expected, 

 since the organic matter and the humus are the bacterial food. 



The investigation also showed wide differences in the bacterial con- 

 tent of the same soil when different crops were growing on it. Thus in 

 simples taken on Aug. 15, there were found in the first twelve inches of 

 a black loam soil bearing timothy and clover, 1,380,000, in the same 

 with alfalfa and clover, 21,091,000, with maize from one to over two 

 millions. In soils from the western part of Kansas, the bacterial con- 

 tent of the same crops was much less (as doubtless is the humus-con- 

 tent), and it is noteworthy that the prairie buffalo grass shows through- 

 out a relatively high bacterial content in the first foot of the soil, ranging 

 next to alfalfa. The root bacteria living on the legumes will naturally 

 increase the bacterial content of the soils on which they grow, more 

 than plants which, like maize, do not directly utilize bacterial action. 



3fnltiplication of the Jlacteria. Marshall Ward and Duclaux have 

 made some special observations in regard to the rapidity with which 

 certain bacteria multiply. Duclaux summarizes the final conclusion 

 thus : taking as a basis the time of 35 minutes for the subdivision into 

 two, which has been frequently observed by Ward, there would be four 

 millions of bacteria produced in twelve hours. The first filaments had 

 plenty of room in a drop culture of one cubic millimeter; but at the 

 end their total volume amounted to the tenth part of the total volume 

 of the drop. At the above rate, making 48 generations in 24 hours, 

 281,500 billions of organisms would be produced. (Grandeau, Ann. 

 Sci. Agron. Vol. i, 1905, p. 456). 



. Icrobic and Anaerobic Bacteria. As may readily be in- 

 fe Ted, the cultural and other surface conditions exert a potent 

 influence both upon the kinds and abundance of the bacteria 

 and molds; since the life-functions of some are dependent upon 



