132 PLANT PRODUCTS 



term for a large group of plant products, which are exuded 

 by wounds and are transparent. Gum arable, obtained from 

 the various species of acacia, is one of the best of these. The 

 gum is obtained by artificia] incision of .4he trees, soon after 

 the end of the rainy season and is collected at intervals 

 of every few days, so long as the weather permits. Trees 

 of about eight to twelve years of age are usually the most 

 productive. Kast Indian gum arable, though shipped from 

 Bombay, is very often not produced in India, but has been 

 collected in other parts and transported to Bombay for 

 shipment. Australian, or wattle-gum, is a product of 

 several specis of acacia, called by the local name of wattle. 

 Gum is much more soluble in hot than in cold water, forming 

 a thick liquid, and is precipitated by alcohol or lead acetate. 

 Although the gums are commonly included in the carbo- 

 hydrate group, their constituents are by no means pure 

 carbohydrate. The chief constituent of gum arable is 

 arabin, which, on hydrolysis, yields arabinose, galactose, and 

 an acid of high molecular weight, C23H38O22, arable acid. 



Agar. — Agar gum, the dried jelly of seaweed, is chiefly 

 obtained from China and Japan, but is very plentiful where 

 there is plenty of seaweed. The special gum contained is 

 known as gelose, which is soluble in water, weak alcohol, and 

 alkalies. Even a solution of | per cent, of agar is faiily 

 solid in ordinary temperatures. Seaweed, when boiled with 

 water, forms the nucleus of many articles of food used in 

 Cornwall and in Japan. It is, however, not easily digested, 

 but is useftd, admixed with milk, in preventing the formation 

 of a hard curd in the stomach. 



Mucilage. —Many seeds of plants, for example Unseed, 

 when macerated with water, produce a thick adhesive 

 mucilage which can be used in place of gum. 



REFERENCES TO SECTION II, A (Sugar) 



Collins, " Value of the Turnip as a Vegetable and Stock Food," Joum. 

 Board of Agriculture, 1916-17, p. 66. 



Collins, " Variation in the Chemical Composition of the Swede," Joum, 

 Agric. Scierhce, i., p. 89. 



