494 CONSTRUCTIVE AND DESTRUCTIVE METABOLISM 



This occurs in the case of the tannins produced during the metabolic changes 

 undergone by the products of photosynthesis, according to G. Kraus and Biisgen, 

 although on other points these authors are not in precise agreement. 



Amygdalin. This glucoside is present in Amygdaleae and a few other plants, 

 but whether it takes an active part in metabolism is uncertain '. The hydrocyanic 

 acid found in Pangium edule, and probably also that occurring in the roots of 

 Manihot utilissima, are produced without the intervention of amygdalin. As a 

 general rule amygdalin is stored in the parenchyma, whereas the ferment emulsin 

 appears to be localized in the vascular bundles, being present in sweet almonds as 

 well as in bitter ones*. During the decomposition of amygdalin by means of 

 emulsin prussic acid is formed, but none when invertin * is the ferment employed, 

 nor is any prussic acid produced when Penirillium glaucum is grown upon a 

 one per cent, solution of amygdalin. 



1ht potassium myronate of mustard seeds seems to be decomposed to a limited 

 extent during germination, probably by means of the ferment myrosin which is 

 stored in different cells 4 . In other cases, however, no enzymatic decomposition 

 occurs during life, for in plants containing indican no blue colouration is produced 

 so long as they are living, although indigo is an aplastic substance and is soon 

 formed after death B . Similarly, the gradual accumulation of alizarin would cause 

 the living root-cells of Rubia tinctoria to become coloured if any were formed 

 by the decomposition of the ruberythric acid present. According to Molisch 

 seedlings of Isatis tinctoria form no isatin in the absence of light, and in darkness 

 any isatin that has already been formed disappears again, being metabolized with- 

 out any production of indigo, although it does not follow that this substance is 

 being continually decomposed in normal metabolism. According to Theorin both 

 popiilin and salicin are consumed in spring, but for the most part even those 

 glucosides which are present in abundance, such as hesperidin, &c., remain intact 

 when the plant is starved*. 



SECTION 88. Pigments. 



These include substances of widely different chemical constitution and 

 physiological importance. With the exception of chlorophyll, etiolin, phyco- 

 phaein, phycoerythrin, bacteriopurpurin, and the pigments of certain bacteria 



1 Jorissen, Bot. Centralbl., 1884, Bd. XX, p. 258; Fortes, Compt. rend., 1877, T. LXXXIV, 

 p. 1401; Wicke, Ann. d. Chem. u. Phann., 1851, Bd. LXXIX, p. 79; 1852, Bd. LXXXI, p. 341. 

 HCN in Manihot, Fliickiger, Pharmakognosie, 1883, 2. Aufl., p. 954; Rochleder, Phytochemie, 



J8 54> P- 54- 



8 Johannsen, Ann. d. sci. nat., 1888, vii. se"r., T. vi, p. 118; Guignard, Compt. rend., 1890, 

 T. ex, p. 477 ; 1893, T. cxvn, pp. 493, 751 ; Green, Annals of Botany, 1893, vn, p. 99. 



* E. Fischer, Ber. d. Chem. Ges., 1894, p. 2990. Cf. Sect. 91. 



4 Spatzier, Jahrb. f. wiss. Bot., 1893, Bd. xxv, p. 75; Smith, Journ. f. Physiol. Chem., 1888, 

 p. 419 ; Nageli, Theorie d. Gahrung, 1879, p. 14; Guignard, Joum. d. Bot., 1894, pp. 67, 85. 



5 Molisch, Sitzungsb. d. Wien. Akad., 1893, Abth. i, Bd. en, p. 269. Cf. also Lookeren, 

 Versuchsst., 1894, Bd. XLIII, p. 401 ; 1895, Bd. XLVI, p. 249. 



6 Pfeffer, Bot. Zeitung, 1874, p. 481 ; Theorin, Bot. Jahresb., 1884, p. 87. 



