30 REPORT OF DEPARTMENT OF BACTERIOLOGY OF THE 
The practice of spreading good soil over land for the purpose of 
increasing its productivity is so old that its origin is lost in antiquity. 
It was doubtless observed that in some cases this application of soil 
had a very marked effect in stimulating the growth of legumes but 
the true reason for this stimulation was first demonstrated by Hell- 
riegel and Wilfarth. They began these investigations in 1883, gave 
a partial report! of their results in 1886 and published them? in full 
in 1888. These investigations demonstrated that the ability of 
legumes to gather nitrogen from the air is dependent upon the pres- 
ence of bacteria, now called Ps. radicicola, within their roots. It 
was found that a small amount of soil from a field in which peas 
had been successfully grown sufficed to inoculate peas growing in 
pots of sterilized sand while a portion of the same soil had no 
effect upon serradella grown under similar conditions. Soil from a 
second field where serradella was growing was efficient in inoculat- 
ing the experimental serradella. 
In these and similar experiments later conducted by other experi- 
menters the soil was not applied directly to the experimental pots but 
a weighed portion of soil was shaken with a measured amount of 
water and after the solids had settled the water was applied to the 
pots. This method was resorted to in order to avoid adding to the 
experimental pots the various insoluble substances which were 
present in the inoculating soils. The results of Hellriegel and 
Wilfarth’s investigations were tested in this way and found correct 
by Prazmowski,? by Lawes and Gilbert, * by Nobbe and Hiltner,® by 
Beyerinck,® and by Atwater and Woods.” 
*Hellriegel, H. Welche Stickstoffsquellen stehen der Pflanze zu Gebote. 
Ztschr. Ver. Riibenzucker Industrie des Deut. Reichs, 1886: pp. 863-877. 
* Hellriegel, H., & Wilfarth, H. Untersuchungen tiber die Stickstoffnah- 
rung der Gramineen und Leguminosen. Ztschr. Ver. Ribenzucker Industrie, 
1888: Beilageheft, pp. 1-234. 
* Prazmowski, Adam. Ueber die Wurzelkndllchen der Leguminosen. 
Bot. Centbl., 36: 1888 and Die Wurzellndllchen der Erbse. Landw. Vers. 
Stat., 37: 161-238. 1890. 
*Lawes, J. B., & Gilbert, H. New experiments on the fixation of nitrogen. 
Proceed. Roy. Soc. Eng., 47: 1890. 
*Nobbe, F., Schmid, E., Hiltner, L. & Hotter, E. Versuche iiber die 
Stickstoff-Assimilation der Leguminosen. Landw, Vers. Stat., 39: 327-359. 
1891. 
*Beyerinck, M. W. Die Bacterien der Papilionaceen-Knollchen. Bot. 
Lip ADs 725. 1600. 
" Atwater, W. O., & Woods, C. D. The acquisition of atmospheric nitro- 
gen by plants. Storrs (Conn.) Agr. Exp. Sta. Rept. 2: 11-§1. 1886. 
