ASSIMILATION OF NITROGEN. 83 



The test for denitrification is best made with fermenta- 

 tion tubes (p. 90), as the entrance of oxygen is here inter- 

 fered with; still, usually test-tube cultures suffice. There 

 occurs an abundant production of gas, which is not ab- 

 sorbed by KHO (not C0 2 ), nor by KHO and pyrogallic 

 acid (not 0), and does not burn (notH or hydrocarbons), 

 therefore is nitrogen. 



According to Stoklasa, the denitrifying action of bacteria 

 is most pronounced in nutrient materials which, like de- 

 cayed vegetable matter, straw, and manure, contain abund- 

 antly the pentose, xylose (C 5 H 10 5 ). Recent litera- 

 ture upon denitrifying varieties : H. Jensen (C. B. L. iv, 

 401), Kiinnemann (C. B. L. iv, 906). Here are also 

 described further denitrifying bacteria : Bact. agile Amp. 

 and Gar., Bacillus Schirokikhi Jensen, Bact. filefaciens Jen- 

 sen, Bact. centropunctatum Jensen, Bact. Hartlebii Jen- 

 sen, Bact. nitrovarum Jensen, Vibrio denitrificans Sev. l 

 Most do not liquefy gelatin and are also able to break 

 up nitrate without the aid of synergetic bacteria. The 

 practical significance of the denitrifying organisms is 

 very great. They rob the soil, manure, etc., of the ni- 

 trates and nitrites which are so necessary for the nourish- 

 ment of plants, and so are powerful enemies of agricul- 

 ture. 



12. Assimilation of Nitrogen. 



While, according to our present knowledge, none of the 

 higher families of plants are able to assimilate nitrogen 

 from the air, this property occurs in one variety of bacter- 

 ium, Bacillus radicicola Beyerinck. This bacterium oc- 

 curs in the small root-tubercles of various leguminous 

 plants 2 (peas, clover, etc.), and may be cultivated from 

 them. It grows poorly or not at all upon the usual nutri- 

 ent media, but well upon an infusion of pea leaves, to 

 which is added 7% gelatin, 0.25% asparagin, and 0.5% cane- 

 sugar. It does not liquefy gelatin, does not form spores 



1 According to Severin (C. B. L. in, 504), there are yet many more 

 denitrifying varieties ; for example, Bacillus subtilis (or closely re- 

 lated varieties), Bacterium indicum, and a coccus. 



2 Regarding the tubercles of the alder which assimilate nitrogen, 

 and theiV inclusion of fungi, see Hiltner (C. B. L. II, 97) . 



