X. 



THE CHEMICAL CONSTITUENTS OF PLANTS 



Glucosides are widely distributed in plants, where they are gener- 

 ally accompanied by the enzymes which are capable of hydrolysing 

 them ; generally, however, the glucoside and the enzyme are contained 

 in different cells and interaction only occurs when the plant tissue is 

 mechanically injured. 



A large number of glucosides have been found in various plant 

 tissues, from which water or alcohol will usually extract them. 



As examples, the following may be mentioned : 



Many of the nitrogen-containing glucosides, e.g., amygdalin and 

 dhurrin, on further hydrolysis, yield their nitrogen as hydrocyanic acid 

 and are thus poisonous (see later in this chapter). 



In some cases, the non-sugar constituents of the glucosides are 

 antiseptic in properties and may thus protect the plant against bacterial 

 attack in case of injury to the tissues. 



II. THE FATS AND WAXES. 



The constitution of the fats has already been briefly described (p. 8). 

 They are glyceryl salts of the fatty acids. The true fatty acids are 

 members of a series of which formic acid, H.COOH, is the first member, 

 acetic acid, CH 3 .COOH, the second, propionic acid, C 2 H 5 .COOH, the 

 third, and so on, each member differing from its predecessor by CH 2 . 

 The general formula for a fatty acid would therefore be C n H 2n+1 .COOH 

 and its structure would be represented most simply and generally by 

 H (CH 2 ) n COOH. 



Such acids are saturated, i.e., cannot combine with other chemical 

 elements or radicals by addition. Included under the title " fatty acids " 

 and occurring in many vegetable fats are acids of a very different type, 

 e.g., crotonic acid, C 3 H 5 .COOH or CH 2 :CH.CH 2 .COOH, a member of a 



