CONSTRUCTIVE AND PLASTIC NITROGEN COMPOUNDS 457 



and amount. This is exhibited most markedly among bacteria, owing to the 

 great powers of adaption possessed by these organisms, but even among 

 the flowering plants great differences may exist between the metabolic 

 products of the members of an order, or even of a genus, while in the 

 same plant, oil and proteids may form the reserve- materials of the seed, 

 sugar and amides those of the rhizome. On the other hand the majority 

 of the species of a given family or genus may produce a particular plastic 

 substance of comparative rarity, such as mannite, dulcite, or glycogen. These 

 peculiarities become still more obvious when attention is paid to those 

 aplastic products which remain permanent constituents of the plant : thus 

 quinine characterizes the genus Cinchona, while the populin of the poplar 

 is replaced by the allied substance salicin in the willow. Even substances 

 which occur comparatively rarely may, however, often be found in plants 

 far removed in systematic position (indigo, cumarin, chrysophanic acid), and 

 there is therefore no general relationship between the systematic position 

 of plants and the chemical nature of their plastic or aplastic metabolic 

 products, as Rochleder 1 supposed. 



SECTION 79. Constructive and Plastic Nitrogen Compounds. 



In addition to the proteids which every plant contains, larger or smaller 

 amounts of other nitrogenous metabolic products are always present, 

 although their functional importance is only known in certain cases. Aspa- 

 ragin and glutamin, leucin and tyrosin are all products which the plant may 

 reassimilate, whereas other amides and amido-acids (viz. phenylamine, 

 amidovalerianic acid, arginin), as well as certain derivatives of urea (xanthin, 

 hypoxanthin, guanin. guanidin, allantoin, adenin, caffein, thein) 2 which may 

 appear during germination or at a later stage, can only with a certain 

 amount of probability be regarded as plastic products. The hydrocyanic 

 acid formed in abundance by Pangium edule and a few other plants 3 

 appears to be used as plastic material, and the same is probably the case 

 with amygdalin. Similarly the nitrates and ammonium salts, which are often 

 stored in great abundance, may be drawn into metabolism again, whereas 

 many other compounds, including alkaloids and glucosides (Sects. 87, 89), 



1 Rochleder, Phytochemie, 1854, p. 259. 



2 A more complete enumeration with regard to higher plants is given by E. Schulze, In wie weit 

 stimmen Pflanzen- u. Thierkorper in chem. Zusammensetzung uberein ? 1894, pp. 14, 19 (Sep.-abdr. a. 

 Vierteljahrsschr. d. Naturf.-Ges. in Zurich, Bd. XXX ix) ; also in Schulze's later works quoted beneath. 

 Whether aspartic and glutamic acid may be actually present is probable but still uncertain. On 

 bacterial products, cf. Flugge, Mikroorganismen, 1896, 3. Aufl., Bd. I, p. 168. According to Kellner 

 (Versuchsst., 1887, Bd. xxxin, p. 378), thein is a plastic substance. 



3 Treub, Ann. d. Jard. bot. de Buitenzorg, 1895, T. xin, p. i. Cf. Sect. 70. 



