144 



The Ohio Xaturalist. 



[Vol. X, Xo. 6, 



note the extent in which the results show clearly that the retarda- 

 tion in growth of wheat plants is not caused by physical or chem- 

 ical conditions but through the direct activity of the bacterial 

 flora. It has long been suspected that a reciprocal relation 

 exists between groups of soil bacteria and the plants growing 

 upon the soil. Various writers have been able to point out that 

 marked differences in the productive power of different soils 

 followed the growth of wild plants, and that these differences 

 persist for some time. It is generally concluded therefore, that 

 the injur}- caused to cultivated plants by weeds or previous crops 

 might be due to influences on the bacterial life in the soil, and in 



Fig. I. WTieat plants growing in i per cent, peptone bog- water solutions 

 inoculated with pure cultures of bog bacteria. Numbers correspond with 

 data in Table III. 



a direction unfavorable to succeeding agricultural crops. That 

 such relations exist the writer is convinced in view of the evi- 

 dence presented above. Xo doubt, the "'exhaustion" of soils 

 which is frequently met with, and which cannot always be 

 attributed to the removal of plant nutrients, is, in part, an allied 

 phenomenon. It cannot remain a matter of indifference to 

 physiological ecologists whether a strong, intimate, and con- 

 trolling relation exists between soil bacteria and surface flora, 

 and how the bacterial organisms affect the character, and the 

 association and succession of plants. At best very little is 

 known of this phase of the physiographic process, and of the 

 reactions and effects of the bacterial products upon plant life. 

 It would be idle, also, to expect that the bacteriological data in 

 themselves are sufficient for a clear interpretation of toxicity 



