128 MAINE AGRICULTURAL EXPERIMENT STATION. 



In the sand, the infection was comparatively limited, though 



some of the nodules developed to great size. In the rich soil 

 the infection was more general and the nodules, though more 

 numerous were much smaller. 



Some of the most careful work done in this direction is that 

 of Hellriegel and Wilfarth* at Bernburg, Germany. In the pot 

 experiments made, it was found that when the soil was not ster- 

 ilized the leguminous plants had tubercles on the roots and there 

 was a noticeable acquisition of nitrogen. W "hen the soil was 

 kept sterile, the plants grew only in proportion to the nitrogen 

 in the soil; the roots had no tubercles and there was no evidence 

 of acquisition of atmospheric nitrogen. 



In the field experiments at Bernburg, the fact that different 

 species of leguminous plants require different kinds of tubercle- 

 bacteria was well shown. 



Xobbe, Schmid, Hiltner and Hotter, having observedj that 

 when soils were inoculated at the surface, only the upper part 

 of the root system produced tubercles, undertook to determine 

 the reason for this.! Some pea plants were set in sterilized sand 

 and supplied only with mineral manures. After forty-one days 

 there were marked evidences of a lack of nitrogen and the soil 

 was inoculated to a depth of 200 mm. with an emulsion of pure 

 cultivated pea-tubercle bacteria. The effect of the inoculation 

 was soon apparent. Within three weeks the plants took on a 

 dark green color and developed rapidly. On harvesting it was 

 observed that only those roots in close proximity to the point of 

 inoculation had produced tubercles, showing the inability of the 

 bacteria to spread to any considerable extent in the soil. The 

 experiment was repeated with like results. "It appears that the 

 distribution of tubercles on the roots is determined by the pres- 

 ence of active bacteria in the soil at the proper place and time.''' 



Schmitter. in Germany, found marked results from the inocu- 

 lation of clay soils with bacteria from the root tubercles of lup- 

 ines. On cultivated soils results were negative, but on soils 

 previously uncultivated the increase in the weight of the lupine 

 plants was from 11 to 32 per cent.§ 



Resume by Wilfarth. Ex. Sta. Record III, 334 (1891). 

 -Land-sv. Vers. Stat. 39, pp. 327-359. 

 jLandw. Vers. Stat. 41, pp. 137, 138. 

 SBot. Centbl. 57 [1894), Xo. 1, pp. 25, 26. 



