362 THE FOOD OF PLANTS 



the carbon dioxide may be liberated by the formation of nitrous acid from 

 ammonia. Godlewski found however that the presence of free carbon 

 dioxide favours the development of nitrite bacteria, and may perhaps 

 influence the growth of pure cultures of nitrate bacteria to a still greater 

 extent, for the oxidation of nitrites to nitrates does not necessarily involve 

 any production of free acid l . 



Nothing certain is known as to the precise character of this process of 

 chemosynthctic assimilation, nor as to the first organic products formed ; 

 neither has it been determined whether a portion of the synthesized carbon 

 compounds is decomposed again with a production of carbon dioxide, 

 nor whether in these organisms any organic material is consumed in re- 

 spiration, the whole of the energy being directly derived from the oxidation 

 of ammonia or nitrites 2 . 



Higher plants are incapable of any such oxidation of ammonia or 

 nitrites, whereas the performance of this process forms an essential 

 condition for the existence of nitro-bacteria, for it has not been found 

 possible to cultivate these organisms in the absence of suitable inorganic 

 nitrogen compounds, and Winogradsky has shown that the results obtained 

 by Burri and Stutzer are due to an error -which readily arises during the 

 slow growth of pure cultures 3 . It is possible, however, that other nitro- 

 bacteria may be found which are able to obtain energy from other sub- 

 stances, and it is even possible that in certain cases the energy for the 

 chemo.synthetic assimilation of carbon dioxide may be obtained by the 

 oxidation of organic substances (Sect. 50). The growth of normally active 

 nitro-bacteria is not hindered by the presence of organic substances, and 

 it is possible that, in addition to the auto-assimilatory products, they may 

 directly absorb appropriate organic food-substances when such are present, 

 for a partial replacement of auto-assimilation is possible in green plants, 

 although the complete inaction of the chlorophyllous organs ultimately 

 induces pathological phenomena terminating in death. 



Heraeus and Hiippe first called attention to the ohemosynthetic assimilation 

 of carbon dioxide by nitro-bacteria, but it is to Winograd sky's researches that our 

 knowledge of these organisms is due, for he was the first to obtain pure cultures 



1 Godlewski, Anz. d. Akad. d. Wiss. in Krakau, Dec., 1892, and June, 1895 ; also Centralbl. 

 f. Bact., 1896, Abth. ii, Bd. II, p. 458. On the corroding action of nitrite bacteria on minerals, &c., 

 cf. Miintz, Cornpt. rend., 1891, T. CX, p. 1370. For researches in which the access of dust, of 

 volatile organic substances, &c., was prevented, see Winogradsky, I.e., Nr. iii, p. 717 : Godlewski, 

 I.e., Dec., 1893. 



" Godlewski (I.e.) found that a certain amount of free nitrogen was liberated, but this might 

 have been derived from the decomposition of ammonium nitrite (cf. Sect. 68). 



8 Burri u. Stutzer, Centralbl. f. Bact., 1895, Abth. ii, Bd. I, p.' 721. Similar erroneous results 

 were obtained by Frankland, Biol. Centralbl., 1891, Bd. xi, p. 56, and Stntzer and Hartleb, Centralbl. 

 f. Bact, 1897, Abth. ii, Bd. Ill, pp. 8, 161. Cf. Winogradsky, I.e., Nr. vii, and Nr. vi, p. 129. 



