ORGANIC SUBSTANCES AS PLANT FOOD 205 



reserves of soluble carbohydrates are often found in such organs. 

 Inulin, for example, is found in the tubers of the Jerusalem arti- 

 choke {Helianthus tuber osus), in the dahlia, and in the roots of 

 chicory, dandelion and other Composite. Upon hydrolysis it 

 gives fructose. Of the disaccharides, sucrose or cane sugar is most 

 often present. In some plants it accumulates in great quantities. 

 Thus, the roots of the sugar beet may contain 20 to 25 per cent 

 sucrose, the fleshy stalks of sugar cane about the same amount, 

 and carrots close to 7 per cent. Sometimes monosaccharides may 

 serve as storage products. Glucose, for example, accumulates in 

 the bulbs of many plants, including the garden onion and its rela- 

 tives. Sugars are likewise found in seeds. Sugar corn and chest- 

 nuts may contain as much as 1 1 per cent of cane sugar, and quite 

 a considerable sugar content is present in the pistachio, almond, 

 and other nuts, which make these sweet to the taste. 



Glycogen, a widely distributed sugar among animals, is not 

 found in higher plants, but it is very common in fungi. Yeast 

 cells may contain 30 per cent of glycogen on a dry-weight basis. 

 Chemically, glycogen is closely related to starch. The only prod- 

 uct of its hydrolysis is glucose. Apparently, it differs from starch 

 only by being in a higher degree of dispersion, upon which depends 

 its greater solubility in water. 



Closely allied to the poly- and disaccharides are the gluco- 

 sides, compounds containing sugar with alcohols of the non-carbo- 

 hydrate type, most frequently those of the aromatic series. The 

 glucosides represent a large group of substances of wide distribu- 

 tion in the vegetable world. They are found often in the food- 

 storage organs. Hence they may be regarded as special kinds of 

 reserve substances, which at germination liberate the combined 

 sugar. Amygdalin is one of the glucosides most prevalent in 

 plants, being found in the seeds of the almond, peach, apricot, 

 plum, apple, and other Rosaceae. It contains glucose, benzoic 

 aldehyde, and prussic acid. The latter splits off very readily and 

 imparts to these seeds a bitter taste. In the bark of various plants 

 is found arbutin, 1 which is composed of glucose and hydroquinone, 

 while the roots of others contain saponins, poisonous glucosides, 

 the nature of which is not yet fully understood. When combined 

 with water they give highly foaming solutions, useful in medicine 



1 Some Rosaceae contain phloridzin, which is composed of glucose and 

 phloretin. 



