

97 



tli« air. They (ii tin mselves on the roots, and cause 

 the tnberclef to grow. Tin- has been proven bj grow- 

 ing clover or beans in soil known to be free from all 

 a. When this was d<»ne no tubercles were 

 formed on the root-, end the plants made i wety poor 

 growth. Kg, I'*- shows the tnberdee formed on the 

 roots of a soy or soja bean plant, which belongs to the 

 pulse family. The bacteria which inhabit the roots of 

 leguminous plants have the 

 power of changing the free 

 en of the air into the 

 compounds of Ditrogen known 

 a- nitrates — and these com- 

 pounds are readily taken up 

 by the plant root-. In this 

 way, as it were the bacteria 

 pav rent to the plant for their 

 homes on rta root-. Why it 

 is that these nitrifying bac- 

 teria live only on the roots of 

 one family of plants is not 

 known, hut they evidently prefer these plants, for so 

 far as we know at present they do not inhabit the 

 of any other family. The family of leguminous 

 plants is a large one. ami -<mie of these plants are found 

 in all -oil- and climate-. In tin- way nature renews 

 ore of Ditrogen in the soil, hut in cultivated fields 

 the conditions are very different. 



Many -oil- do not contain any of the bacteria which 

 change the nitrogen of the air into nitrates. In -in h 

 soils no tubercles form on the roots of legumes, which 

 7 



Flo. W.— Roots of yellow 

 soy bean, grown at the Kan- 

 pas Agricultural Experiment 

 station in 1800. on land inoc- 

 ulated with an extract 

 talnlngthe tubercle-forming 

 bacteria. (Prom Yearbook, 

 U.S. Dept.Agr. 18B7.) 



