4 o6 THE FOOD OF PLANTS 



Most fungi, including the common moulds, and such bacteria as are able to 

 develop when supplied with nitrogen in the form of ammonium nitrate, grow better, 

 indeed often much better, when fed with peptone, amides, or other organic 

 nitrogen-compounds. Peptone is in fact essential for many such plants, whereas 

 for others, amides afford a more or less suitable source of nitrogen : thus Bacillus 

 perlibratus^ prefers asparagin to peptone, as do Rhizopus oryzae and Chlamydomucor 

 oryzae*, for which urea also affords an adequate source of nitrogen. 



Chemical constitution and nutritive value. A great variety of nitrogen-com- 

 pounds may serve as food-material for large numbers of plants or for special 

 ones only, and the general remarks previously made in connexion with the 

 carbon-compounds (Sect. 66) apply equally well here, for substances of similar 

 chemical constitution may have widely different nutritive values. No doubt 

 a detailed study of the nutrient properties of different proteids would reveal 

 the existence of numerous specific differences. No general conclusions can be 

 drawn from experiments made upon a few plants, for different plants have widely 

 different specific needs. Nageli's supposition that nitrogen cannot be assimilated 

 when in direct combination with carbon has proved to be incorrect, for certain 

 fungi are able to grow when supplied with nitriles s , and may even obtain their 

 nitrogen from amygdalin or potassium cyanide (Pfeffer). According to the 

 researches of Treub, hydrocyanic acid normally takes part in the metabolism of 

 Pangium edule*. Free nitrogen is utilized by certain organisms, while nitrites are 

 assimilated by nitrite bacteria, although they do not serve as a source of nitrogen 

 for Phanerogams or mould-fungi 5 ; it is even possible that nitrous oxide may be 

 assimilated by certain organisms 6 . 



According to Knop and Wolff 7 , Phanerogams are unable to assimilate 

 nitrobenzoic acid, amido-benzoic acid, morphine, quinine, cinchonine, caffein, 

 ferrocyanide and ferricyanide of potassium; these substances hardly seem to 

 be suitable even for the nutrition of mould-fungi, although sufficient atten- 

 tion has not yet been paid to their poisonous action. Caffeine, quinine, and 



4. Aufl., p. 128; Nageli, Bot. Mitth., 1881, Bel. in, p. 399; Laurent, I.e., and the works already 

 quoted. Bacteria: Nitrobacteria, Sect. 23; also Fermi, Centralbl. f. Bact., 1891, Bd. x, p. 405 ; 

 A. Fischer, Jahrb. f. wiss. Bot., 1895, Bd. xxvil, p. 52. 



1 Beyerinck, Centralbl. f. Bact., 1893, Bd. xiv, p. 834. 



2 Went und Prinsen Geerligs, Bcob. iiber die Hefearten d. Arrakfabrikation, 1895, p. 21. On 

 the different forms of yeast, see Beyerinck, Centralbl. f. Bact., 1892, Bd. XI, p. 68, and 1894, Bd. 

 xvi, p. 57, &c. ; on Bacteria, Beyerinck, Aliment photogene, 1891, pp. 19, 51 (Sep.-abdr. aus 

 Archiv. Neerland., T. xxiv) ; Bot. Zeitung, 1891, p. 740, and the other literature quoted here and 

 in Sect. 66. See also Linossier, Centralbl. f. Bact., 1892, Bd. in, p. 112. 



3 Reinke, Unters. a. d. Bot. Lab. in Gottingen, 1888, III, p. 37. 



4 Ann. d. Jard. hot. d. Buitenzorg, 1895, XIII, p. i. 



5 Birner und Lucanus, Versuchsst, 1866, Bd. VIII, p. 128, for Phanerogams ; Raulin,!. c., p. 229, 

 for fungi. On the poisonous action of nitrates, cf. Molisch, 1877, 1. c., p. 234. On nitrite formation, 

 see Sect. 102. 



6 Lamartina's positive conclusions (Chem. Centralbl., 1881, p. 649) are not based upon sufficiently 

 decisive results. 



7 Knop und Wolff, Versuchsst., 1865, Bd. vn, p. 308. Cf. also Bot. Centralbl., 1883, Bd. xvi, 

 p. 113. 



