GLUCOSIDES, TANNIN, AND PHENOLS 493 



of methyl-blue, and also that in the roots of Trianea, &c., tannin is produced 

 only at certain stages of development, no renewed formation being induced by 

 the precipitation of all that present in the cell. This is certainly not always 

 the case, for the formation of callus-tissue and of galls is often associated 

 with a marked production of tannin, which, like other benzene derivatives, 

 may probably be produced either by synthesis or by dissociation l . During 

 the synthesis of proteids a formation of aromatic radicles is necessary, 

 provided none such are present in the food, but the process is not dependent 

 upon the pre-existence of benzene derivatives. 



Analogy with fungi, as well as the absence of any accumulation of 

 aromatic bodies even during active and prolonged proteid decomposition, 

 leaves no doubt that benzene derivatives may be reassimilated under certain 

 circumstances in the higher plants as well as in the lower. Certain glucosides 

 may at any rate be decomposed, and the presence of appropriate enzymes 

 enables such decompositions to take place during life or after death. In 

 the higher plants glucosides and their respective ferments are as a general rule 

 deposited in different tissues, but in unicellular organisms the two substances 

 may be present in the same cell though not in direct contact. All post- 

 mortem changes and decompositions are of course not necessarily due to 

 the presence of enzymes in the dying cell or tissue. 



Tannin. This is a technical term which has no precise chemical or physio- 

 logical meaning, for the same microchemical tests with iron salts and potassium 

 bichromate are given by various phenols and phenol compounds, but not by others 

 such as phloroglucin, &c., which have a similar physiological importance 2 . The 

 latter can hardly, however, apply to all the aromatic substances, glucosides, and 

 compounds of phenols with other substances, which are classed together as 

 tannins because of their similar microchemical reactions. Moreover, since the 

 same substance may serve several different uses, it is hardly possible to predict 

 that the classification into plastic, aplastic, pathological and other tannins will 

 be of any great importance 3 . 



In spite of numerous recent researches 4 but little is known as to the function 

 of tannin. Most tannin substances seem to be aplastic, and certain contradictory 

 statements made long ago by Wigand and Schell have not been confirmed or have 

 become doubtful. Tannin very commonly disappears from the spot where it was 

 produced, and 'accumulates at other points where it remains unaltered during life. 



1 The discussion as to whether proteids or carbohydrates yield the material for the formation of 

 tannins, &c., is devoid of importance. Cf. G. Kraus, 1. c., 1889, p. 45 ; Mielke, 1. c., 1894, p. 281. 



* Waage, Ber. d. Bot. Ges., 1890, p. 290; Nickel, Bot. Centralbl., 1891, Bd. XLV, p. 394; 

 Reinit/er, Lotos, 1891, Bd. XI (Separatabh.) ; Mielke, Bot. Centralbl., 1894, Bd. LIX, p. 280. 



8 Cf. Hansen, Pflanzenphysiol., 1890, p. 119 ; Wagner, Journ. f. prakt. Chemie, 1866, Bd. XCIX, 

 p. 294. 



4 G. Kraus, Grundlinien z. Physiol. d. Gerbstoffs, 1889 ; Biisgen, Verhalten d. Gerbstoffes in der 

 Pflanze, i889(Zeitschr. f. Naturw., Jena, Bd. xxiv) ; Mielke, 1. c. ; Kiistenmacher, Jahrb. f. wiss. Bot. 

 1894, Bd. xxvi, p. 118. 



