NUTRITIVE VALUE OF DIFFERENT NITROGEN COMPOUNDS 405 



not at all. In an ordinary soil traces of nitrates are continually being formed 

 by the action of micro-organisms. Any accumulation is rapidly removed in the 

 drainage water since the soil has hardly any power of retaining nitrates, and 

 aquatic Phanerogams and Algae ' hence can obtain a sufficient supply of the 

 nitrates they seem to prefer from the river or spring-water in which they grow. 

 Neither Phanerogams nor Algae appear to have the power of forming nitrates from 

 ammonium salts by oxidation, and the accumulation of nitrates exhibited by certain 

 plants occurs only when an abundant external supply is provided ". 



Phanerogams and Algae can also employ various organic substances as more 

 or less valuable sources of nitrogen : urea, glycocoll, asparagin, leucin, tyrosin, 

 guanin, kreatin, hippuric acid, uric acid, acetamide, propylamine ", but none of 

 these is so favourable to growth as saltpetre. All these substances seem to be 

 directly absorbed and assimilated without the aid of micro-organisms. According 

 to Wagner (1869), hippuric acid is decomposed by plants into glycocoll and benzoic 

 acid, the latter of which is useless. The parts of the plant where such decom- 

 positions occur are probably the same as those in which proteids are synthetized, 

 but neither process has as yet been precisely localized. Under natural conditions 

 Phanerogams rarely absorb organic nitrogen-compounds, whereas carnivorous plants 

 are specially adapted to obtain supplies of peptone, and for many symbionts organic 

 nitrogen-compounds appear to be an absolute necessity (Sect. 64). 



Fungi, Bacteria, &>c. Among heterotrophic plants the nitrogen-fixing Clos- 

 tridium Pasteurianurn cannot be fed with organic nitrogen-compounds, and many 

 of the common moulds as well as a whole host of bacteria grow well when 

 supplied with ammonium nitrate, for some the nitric acid, for others the ammonium 

 base being the preferable source of nitrogen 4 . The latter is especially the case with 

 organisms which are entirely or partially anaerobic, and hence grow in media 

 where no formation of nitrates is possible. Thus certain yeasts and bacteria 

 can grow when supplied with ammonium salts but not when nitrates afford the 

 sole source of nitrogen 5 , whereas a few strongly aerobic bacteria can make use 

 of the latter compounds. 



1 Kossowitsch, Bot. Zeitung, 1894, p. 109. On the organic nitrogen compounds of the soil, see 

 Berthelot, Compt. rend., 1891, T. cxii, pp. 189, 195. On mycorhiza in forest soils, cf. Sect. 65. 



2 Molisch, Sitzungsb. d. Wien. Akad., 1887, Bd. xcv, p. 221 ; Frank, Ber. d. Bot. Ges., 1887, 

 p. 472; Schimper, Bot. Zeitung, 1888, p. 121 ; Serno, Landw. Jahrb , 1889, Bd. xvnr, p. 876; 

 E. Schulze, Zeitschr. f. phys. Chem., 1896, Bd. xxn, p. 82, and the lit. here quoted. Laurent found 

 the same to be the case in mould-fungi (Ann. d. 1'Inst. Pasteur, 1889, T. in, p. 371). 



3 Such experiments were performed by means of water-cultures by Hampe, Versuchsst., 1865, 

 Bd. vii, p. 308 ; 1866, Bd. vm, p. 255 ; 1867, Bd. ix, p. 49 ; 1868, Bd. x, p. 180 ; Knop und Wolff, 

 ibid., 1865, Bd. vii, p. 463, and Chem. Centralbl., 1866, p. 744; Birner und Lucanus, Versuchsst., 

 1866, Bd. vm, p. 128; Beyer, ibid., Bd. ix, p. 480; Bd. XI, p. 270; W. Wolff, ibid., Bd. x, p. 13; 

 P.Wagner, ibid., Bd. xi, p. 292; Bd. xin, p. 69; Bente, Bot. Jahresb., 1874, p. 838; Baeseler, 

 Versuchsst., 1886, Bd. xxxni, p. 230; Hansteen, Ber. d. Bot. Ges., 1896, p. 362. Johnson (Ver- 

 srchsst., 1866, Bd. vm, p. 235), Ville (Compt. rend., T. LXV, p. 32), and Cameron (Jahresb. d. 

 Agr.-Chem., 1861-2, p. 145) used sand as a medium. [Lutz, Compt. rend., cxxvi, 1898, p. 1227.] 



* See Laurent, Ann. d. 1'Inst. Pasteur, 1889, T. in, p. 368; also Nageli, Bot. Mitth., 1881, 

 Bd. in, p. 399; Fitz, Ber. d. Chem. Ges., 1876, p. 1540; Raulin, Ann. d. sci. nat., 1869, v. ser., 

 T. xi, p. 226. 



5 Yeast: Ad. Mayer, Unters. iiber d. ale. Gahrung, 1869, p. 69, and Gahrungschemie, 1895, 



