78 CHEMISTRY OF PLANT LIFE 



C 6 H 5 

 (6) CeHnOs-O-CH + H 2 = C 6 H 5 'CHOH.CN -I- C 6 Hi 2 6 



Mandelo-nitrile I Mandelo-nitril- Glucose 



glucoside 



(c) CeHs-CHOH-CN -f H 2 = C 6 H 5 -CHO 4- HCN 



Mandelo-nitrile Benzaldehyde Hydrocyanic 



acid 



GENERAL PROPERTIES OF GLUCOSIDES 



As a rule, glucosides are easily soluble in water. They are 

 generally extracted from plant tissues by digestion with water or 

 alcohol. In most cases, the enzyme which is present in other cells 

 of the same tissue must be killed by heating the material, in a 

 moist condition, to the temperature of boiling water, before the 

 extraction is begun, as otherwise the glucoside will be hydro- 

 lyzed as rapidly as it is extracted from its parent cell. Macera- 

 tion or otherwise bruising the tissue, after the enzyme has been 

 destroyed, facilitates the extraction. The glucosides, after extrac- 

 tion and purification by recrystallization, are generally colorless, 

 crystalline solids, having a bitter taste and levorotatory optical 

 activity. This latter property is remarkable, as most of them are 

 compounds of the strongly dextrorotatory d-glucose. 



Many of the natural glucosides have marked therapeutic 

 properties and are largely used as medicines; others are the mother- 

 substances for brilliant dyes; for example, indican, from which 

 indigo is obtained, and the alizarin glucosides. 



Several hundred different glucosides have been isolated from 

 plant tissues, and their properties described, and this number is 

 being added to constantly, as the methods of isolation and study 

 are improved. They may be classified into groups, according to 

 the nature of the organic compound other than sugars which they 

 yield when hydrolyzed. The following descriptions of the occur- 

 rence, constitution, products of hydrolysis, and special properties 

 of typical members of each of the several different classes of glu- 

 cosides will serve to illustrate their general relationship to plant 

 growth. 



