CHEMICAL COMPOSITION OF PLANTS 41 



The most common dissacharide in plants is sucrose or cane 

 sugar, which consists of 1 molecule of glucose joined to 1 of 

 fructose. This sugar crystallizes readily and has an intensely 

 sweet taste. It is frequently stored in the various organs of 

 plants and is obtained in large quantities from the roots of sugar 

 beets, which contain up to 20 to 25 per cent of sucrose, and, 

 from sugar cane, sugar maple, and several other plants. By 

 the action of dilute acid as well as of a special enzyme invertase, 

 sucrose may be easily hydrolyzed; i.e., by the introduction of 

 1 molecule of water, it disintegrates into equal proportions of 

 c^-glucose and (i-fructose. This process is termed 'inversion." 

 From insufficiently precise methods of sugar analysis, the pre- 

 vious assumption was that plants frequently contained another 

 disaccharide, maltose, which disintegrates on hydrolysis into 2 

 molecules of <i-glucose. On the basis of further investigations 

 (Davis, 1915-1916, and others), it has been established that 

 maltose is very seldom found in the leaves of plants and in most 

 cases is completely absent. 



Closely allied to disaccharides is the group called '^glucosides.'^ 

 These are compounds of sugars with other substances, such as 

 alcohols, phenols, aldehydes, and acids. Glucosides are very 

 widely distributed in the vegetable world. They are found 

 very often in the food-storage organs. Hence, they may be 

 regarded as special kinds of reserve substances, which at germina- 

 tion liberate the combined sugar. Amygdalin is one of the gluco- 

 sides most prevalent in plants, being found in the seeds of the 

 almond, peach, apricot, plum, apple, and others of the family 

 Rosaceae. Hydrolysis of this glucoside liberates glucose, benz- 

 aldehyde, and hydrocyanic acid. The last splits off very 

 readily and imparts to these seeds a bitter taste. The bark of 

 various trees, as well as the seeds of lupine and several other 

 plants, contains arbutin, which is composed of glucose and 

 hydroquinone, and the roots of many plants contain saponins, 

 poisonous glucosides, the nature of which is not yet fully under- 

 stood. When combined with water, they give foaming solutions 

 useful in industry, e.g., soap root. The toxicity and sharp taste 

 of many glucosides lead to the suggestion that they serve as 

 protecting substances, preserving the seeds and other parts of 

 the plant from being eaten or injured by animals. 



