HOFFMANN: SOIL PRODUCTIVITY. 1)1 



seedlings in the normal soil extract, and B. subtilis show a 

 very sparse root development. It is suprising, however, that 

 despite these pronounced differences in root development, there 

 should be such slight differences in the developments of the 

 tops. 



In another test corn seedlings were employed with extracts 

 from samples of black marsh soil in which the following or- 

 ganisms were grown : 



1. Azotobacter. 



2. B. denitrificans. 



3. Proteus vulgaris. 



4. Normal soil. 



5. Cladothrix odorifera. 



6. Yellow ammonifier. 



7. Manure organism (B. mycoides?) 



8. Sterile soil. 



In this series Cladothrix odorifera and Proteus vulgaris oc- 

 casioned a more luxuriant development in the case of corn and 

 a marsh soil. In the case of the denitrifier the poorest de- 

 velopment of the corn seedlings was secured. Here again the 

 differential influence seemed to be confined more to the root 

 than to the leaf system. 



In this manner a large series of experiments (20) have been 

 performed in which one or the other of the three factors in- 

 volved has been modified. As typical of the results secured 

 in these experiments, the data in tables II, III and IV are 

 presented. One finds here marked variations both in the size 

 of crop and in the dry weight of same as influenced by the 

 various cultures. It is interesting to note that the manured 

 soils (5 per cent finely ground dry manure) invariably show 

 a larger gram yield than the unmanured soils ; the two ex- 

 ceptions being in the case of corn and clover in the extracts 

 made from the soil inoculated with Proteus vulgaris. If one 

 measures the influence of the organisms by the weight of crop 

 grown upon the extracts, one finds marked variations. In 

 duplicate experiments where all three factors were identical, 

 similar results are invariably secured, showing that whatever 

 influence is exerted, the same is constant as long as the con- 

 ditions remain the same. A change in any one of three factors 

 occasioned a change in the influence exerted. Note the much 

 larger yield of corn on the manured soil with B. prodigiosus in 



3— Univ. Sci. Bull., Vol. IX, No. 7. 



