HOFFMANN : SOIL PRODUCTIVITY. 



97 



Table III. — Influence of soil extracts from sterilized soils in which certain organisms 

 had been grown upon the growth of wheat seedlings. 



Organism. 



Normal soil flora 



Sterile soil 



( 'ladothrix odorifera 



Azotobacter 



B. prodigiosus 



H. proteus vulgaris 



Ammonifier 



Normal soil 



B. denitrificans . 



Table IV. — Influence of soil extracts from sterilized soils in which certain organisms 

 had been grown upon the growth of clover seedlings. 



Table V. — Influence of the extracts of variously cropped soils upon the rate of multi- 

 plication of one of the ammonifying organisms. Number of bacteria per cc. of extract. 



