PROCESSES BY WHICH NITROGEN IS ASSIMILATED 407 



many alkaloids have, however, a feeble nutrient value for certain fungi and 

 bacteria. 



SECTION 71. The Character of the Processes by which 

 Nitrogen is assimilated. 



Both higher and lower plants are able to construct proteids as well 

 as many other organic nitrogen compounds from nitrates and ammonia. 

 Certain of these, namely, amides, may at times be present in greater 

 abundance than the proteids, but the character of the processes by 

 which these substances are produced forms one of the many unsolved 

 problems of metabolism, and will remain so as long as merely the starting- 

 point and the end-product are known. Without doubt these synthetic 

 processes involve a variety of complicated changes and interactions, and 

 it is permissible to regard the simpler organic nitrogen-compounds as stages 

 in the formation of proteids whenever the plant can produce them syntheti- 

 cally, and can use them at a later period-stage in the synthesis of proteids. 

 Asparagin and other amides : are substances of this character which are 

 found in higher plants, and are often produced in large amount by proteid 

 decomposition, while they may again be synthetized to form proteids. 

 This fact, however, says but little as to the actual synthesis of proteids, 

 which fungi are able to form from nitrates or ammonium salts, as well as 

 from amides. The study of fungi is especially likely to afford a glimpse 

 into these processes of constructive metabolism, owing to the fact that 

 the external and cultural conditions can be varied to so considerable an 

 extent. Those fungi to which amides and peptones must be supplied are 

 organisms which have lost the power of producing amides and proteids 

 synthetically. It may be found possible to inhibit this power entirely in 

 such a fungus as Penicillium, or to prevent the final stages of proteid- 

 synthesis, and thus to obtain important data for the solution of the 

 problem with which we are concerned. Isolated facts can only be 

 interpreted with the utmost care, for if any conclusions are to be drawn 

 from the fact that fungi are able to obtain their nitrogen from nitrites, the 

 same importance would necessarily also be given to cyanides. In the case 

 of Phanerogams, if attention were paid solely to Pangium ednle, it might 

 be concluded that hydrocyanic acid always formed a stage in the formation 

 of proteids. 



Plants can induce molecular disintegrations and reconstructions of 

 the most diverse character. Penicillium is able to form all the substances 



1 Literature: Kellner, Landw. Jahrb., 1879, Suppl.-Bd. vm, p. 243; Emmerling, Versuchsst., 

 1880, Bd. xxiv, p. 113, and 1887, Bc ^- xxxiv, p. 73; Hornberger, ibid., 1885, Bd. xxxr, p. 415; 

 Serno, Landw. Jahrb., 1889, Bd. xvin, p. 905; E. Schulze, ibid., iSSS, Bd. xvn, p. 704. 



