NITROGENOUS METABOLISM 463 



practically the same end-product is produced, the difference being that the 

 fungus avoids any injurious accumulation or alkalinity by excreting oxalic 

 acid or by other means (Sect. 86). It is extremely doubtful whether the 

 lower animals produce urea, and this never seems to be formed in vegetable 

 metabolism although various derivatives of uric acid may appear. In the 

 higher plants the decomposition of proteids appears as a general rule only 

 to proceed as far as the formation of amides, &C. 1 , and the fact that these 

 remain present in starved plants shows that the latter are unable to satisfy 

 their requirements or to obtain a sufficient supply of energy by the disin- 

 tegration of amides, although this power is actually possessed by certain 

 fungi. It is always possible that exceptions may occur ; indeed the hydro- 

 cyanic acid, trimethylamin, &c. formed by certain plants may be normal 

 end-products of proteid metabolism, especially when the latter is artificially 

 stimulated. Many lower organisms excrete amides and other nitrogenous 

 substances which are produced during putrefaction. 



It appears therefore that all plants are capable of inducing proteid 

 decomposition, as is shown by the fact that a marked accumulation of 

 asparagin and other amides takes place in cut branches of trees, herbs, 

 mosses, &c., or in intact plants kept in darkness or in air deprived of 

 carbon dioxide, or in the apices only of branches, &c. when they are kept in 

 darkness 2 . Borodin ascribes this entirely to the insufficiently active re- 

 generation of the amides produced, but apparently an increased activity of 

 proteid-decomposition is induced at the same time, for we are dealing here 

 only with a special case of a phenomenon common to all plants, and since 

 an increased proteid-decomposition accompanies a deficiency of non-nitro- 

 genous food in fungi and in animals 3 it seems permissible to assume that 

 a similar correlation exists here also. At the same time different nitro- 

 genous substances may partially, totally, or mutually protect one another, 

 as for example when the presence of nitrates inhibits the assimilation of free 

 nitrogen (Sect. 70), and in many other cases as well (Sects. 67, 93). The 

 decomposition of proteids probably continues without cessation even in adult 

 plants which are well supplied with non-nitrogenous organic food, yielding an 

 adequate supply of energy and sufficing for the maintenance of organs which 

 have ceased to grow. Definite proof of this fact may possibly be obtained 

 by a critical study of those organisms which are incapable of regenerating 

 proteids and in whose excreta certain of the products of proteid-decom- 

 position must therefore appear, as is the case in the higher animals. 



1 The formation of traces of ammonia by seedlings is possible, but still doubtful. Cf. Hosaeus, 

 Jahresb. d. Agr.-Chemie, 1867, p. 100; Sabanin u. Laskovsky, Versuchsst., 1875, Bd. XVIII, p. 407 ; 

 E. Schulze, Landw. Jahrb., 1878, Bd. vir, p. 420; iSSo, Bd. ix, p. 15. 



2 First observed by Borodin, Bot. Zeitung, 1878, p. Soi ; also E. Schulze, Landw. Jahrb., 1880, 

 Bd. IX. p. 25; O. Muller, Versuchsst., 1887, Bd. xxxm. p. 327. 



3 Neumeister, Physiol. Chemie, 1893. Bd. I, p. 293. 



