CONSTRUCTIVE AND PLASTIC NITROGEN COMPOUNDS 459 



As the reserve-materials are consumed, the amount of amides present in the 

 vegetative organs decreases until an approximate general average of from 10 to 20 

 per cent, is reached 1 . The amount of amides decreases in old organs, unless 

 they are utilized as storage-receptacles. A ripe potato contains from 30 to 47 

 per cent, of its nitrogen in the form of amides, and similar amounts are present 

 in the beet-root, root of Scorzonera, &c. 2 The potato contains asparagin in 

 greatest abundance, along with a little tyrosin and leucin, and a trace of glutamin, 

 whereas the latter is the most abundant amide in the beet-root, which also contains 

 a certain quantity of betain. These different amides can replace one another 

 just as may various proteids or carbohydrates, but asparagin appears to be the 

 most abundant and widely distributed of them, and it has been detected even in 

 Agaricineae and certain of the Myxomycetes 3 . It is possible that asparagin may 

 be formed by a few bacteria, for in the metabolism of putrefactive and other forms 

 a great variety of nitrogenous compounds may be produced. 



Proteids form a class of substances of the highest physiological im- 

 portance, and owing to the complex nature of their large molecules they 

 offer a much greater variety of possible combinations than carbohydrates 

 do. There can be no doubt that many readily decomposable proteids are 

 continually being formed by the living organism, and that even many 

 stable proteids may exist of which we have as yet no conception. The 

 complex nature of proteids and their multifarious chemical affinities not 

 only render them suitable for the constitution of the living protoplast but 

 also make them adapted to serve a variety of other purposes. Dis- 

 regarding the chitinous substance which takes part in the formation of the. 

 cell-wall in fungi, many proteids may be stored or translocated as plastic 

 material, while enzymes and tox-albumins have a special functional or 

 biological importance, and particular proteids or proteid compounds may 

 be employed for similar purposes. 



The protoplast is apparently mainly built up of proteids, which may 

 form not less than 40 per cent, and perhaps not more than 90 per cent, of 

 the dry weight of the protoplasm, after the metaplasm, &c. has been 

 removed. The living plasma forms a certain proportion only of the cell 

 and its relative bulk is often very small, so that the amount of proteids 



also in Landw. Jahrb., 1880, Bd. ix, p. i ; 1883, Bd. xii, p. 99J l888 M - XVII P- 68 3 ? l8 9t 

 Bd. xxi, p. 105 ; Versuchsst., 1895, Bd. XLVI, p. 394 J 1896, Bd. XLVIII, p. 33 5 Zeitschr. f. physiol. 

 Chemie, 1896, Bd. XXII, pp. 411, 435- Cf. also Prianischnikow, Versuchsst., 1894, Bd. XLV, p. 247 ; 

 1896, Bd. XLVI, p. 459 ; Frankfurt, ibid., 1894, Bd. XLIII, p. 144: I 8 95. Bd. XLV P- X 53- Various 

 details concerning individual substances are given by Ebermayer, Zimmermann, Mikrotechmk, &c. 



1 Kellner, Landw. Jahrb., 1879, Bd. vni, p. 245; Emmerling, Versuchsst., 1880, Bd. XMV, 

 p 113 ; E. Schulze, Landw. Jahrb., 1880, Bd. ix, p. 27 ; 1881, p. 686 ; Versuchsst., 1887, Be 



p. 89. A partial summary is given by Ebermayer, Physiol. Chemie, 1882, pp. 627, 664 ; a] :>mg, 

 Nahrungs- u. Genussmittel, 1889, 3. Aufl., Bd. I, p. 641. 



2 Cf. Kellner, I.e.; Schulze, Versuchsst, 1882, Bd. xxvii, p. 357: Kbcrmayer, I.e. 



3 Reinke, Unters. a. d. Bot. Lab. in Gbttingen, 1881, Heft a, p. 166. 



