GLUCOSIDES, TANNIN, AND PHENOLS 491 



f diosmosing substances, for the alkalinity is not altered by repeated washing with 

 water. Free acids, however, usually diosmose readily, and hence it must be 

 determined in each separate case whether the loss of acid is prevented by the 

 diosmotic properties of the plasmatic membranes, or by the formation of acid salts 

 (Sects. 1 6, 22). A diminution in the acid reaction of the cell-sap may be produced 

 by an increased formation of alkali, by a consumption of acid, or by union with 

 basic substances. It has already been mentioned that the absence of certain sub- 

 stances from a nutrient medium may cause an acid or an alkaline reaction to be 

 produced in it or in the cell-sap, and that a strong acid may be set free by a weak 

 one according to the principle of action in mass 1 . Plants possess great capabilities 

 in virtue of their osmotic powers, and it is even possible that an alkaline protoplast 

 may gradually excrete large quantities of free acid, and thus render possible the 

 digestive action of peptic ferments. Magnesium phosphate and many other 

 substances may remain dissolved in an acid cell-sap, whereas they are are at once 

 precipitated if it becomes alkaline. 



SECTION 87. G-lucosides, Tannin, and Phenols. 



Probably every plant produces one or other of the numerous benzene 

 derivatives, of which some occur in particular plants only, while others, 

 such as tannin and phloroglucin, are widely distributed 2 . All these sub- 

 stances are often found in combination with other bodies as glucosides 

 and similar compounds, and probably numerous unstable combinations exist 

 in the living plant which decompose on death, and hence have not as yet 

 been detected. The ester-like compounds of carbohydrates with aromatic 

 radicles form substances (glucosides) 3 which diosmose with difficulty, and 

 from which the carbohydrates may subsequently be liberated, the aromatic 

 component remaining intact in the cell or at a later stage reuniting with 

 carbohydrates 4 . Certain glucosides appear to behave as aplastic products, 

 whereas others may be entirely reassimilated. Fungi appear to be capable 

 of decomposing almost all glucosides (viz. arbutin, salicin, phloridzin, 

 quercitrin, glycyrrhizin, amygdalin). 



Fungi can assimilate many aromatic bodies, such as tannin, resorcin, 



1 Cf. Sect. 28. Animals are able to produce large quantities of free hydrochloric acid, but not 

 plants. Bunge, Physiol. Chemie, 3. Aufl., p. 143. On the sensitivity of many protoplasts to acids, 

 cf. Pfeffer, Osmot. (inters., 1877, p. 135. 



a Waage, Ber. d. Bot. Ges., 1890, p. 250. On the artificial production of glucosides of phloro- 

 glucin, cf. Councler, Ber. d. Chem. Ges., 1895, p. 24. On the microchemical tests for these 

 substances, see Zimmermann, Mikrotechnik, 1892, pp. 82, 89, no. 



3 Cf. E. Fischer, Die Chemie d. Kohlenhydrate, Rede, Berlin, 1894; Ber. d. Chem. Ges., 1894, 

 pp. 24, 78 ; Tollens, Handb. d. Kohlenhydrate, ir, 1895, p. 84. It is mainly glucosides of aromatic 

 substances that have been found in plants. 



* Cf. Sect. 22. Pfeffer, Unters. a. d. Bot. Inst. z. Tubingen, 1886, Bd. n, p. 309; Moller, Ber. 

 d. Bot. Ges., 1886, Generalvers., p. Ixx; Mielke, Bot. Centralbl., 1894, Bd. LIX, p. 381. All carbo- 

 hydrates are not produced by the decomposition of glucosides, as Rochleder supposes (Phy tochemie, 

 1854, p. 328). 



