112 DESCRIPTIVE BOTANY. 



Etymology and History. — Acacia i& horn the Greek aKUKia, a name given 

 to a thorny plant by Dioscorides, derived from aK-f], a sharp point. Senegal, 

 the specific name, is from the district in Africa where the tree abounds. 

 Gum Arabic, the popular name, is due to the circumstance that formerly the 

 gum was carried from Aden in Egyptian ships through the Hed Sea to Egypt, 

 and thence reshipped to Europe. 



At present none of the gums of commerce known as Gum Arabic are 

 obtained from Arabia. 



The pure gum used in medicine is from Kordofan, is carried down the Nile to 

 Egypt, and is a white opaque substance Avhicli when pulverized resembles wheat 

 Hour in color. Tlie several gums sold for gum arable are from other species, 

 and are usually brought to market mixed. 



The gum exudes from wounds or incisions in the bark, and appears in 

 tears from the size of a pea to that of a small hen's-egg. The different 

 sorts are knoAvn in commerce by names which indicate the countries wlience 

 they are brought, as Mogador gum, North Africa gum, Jedda gum from 

 Jedda in Arabia, Cape gum from the Cape of Good Hope. East India 

 gum is carried from the east coast of Africa to Bombay, from which p(jint 

 it is shipped to Europe. 



There is also a gum sold for gum arabic -svhich is an Australian product, 

 and is obtained from the Acacia pycnantha, Benth. The beautiful A. dealbata 

 of Australia, frequently seen in our green-houses, yields a good gum. 



The Acacia Seyal is the Shittim Avood of Scripture, and the Acacia Suma 

 is one of the sacred trees used by the Brahmins to obtain fire by friction, for 

 their altars. 



The fine white gums of commerce are known as Turkey gums. The darker, 

 translucent, reddish gums are known commercially as Senegal gum. 



Use. — The gum begins to flow in the flowering season early in December, 

 and the liarA'est extends to the last of January, during which time the har- 

 vesters sul)sist almost entirely upon the gum. 



^1. Catechu of India yields by decoction a valuable tonic (Catechu), and in 

 the hands of the dyer it forms the colors black, brown, green, drab, -diwd fawn. 

 The decoction is higlily charged with tannin. 



As a medicine, gum arabic is used largely as an emollient and demulcent; 

 it is prescribed in stomach difliculties, dysentery, and other bowel disorders; 

 and is used in throat troubles, and for cough mixtures. 



In confectionery, it is mixed with sugar and formed into lozenges and gum- 

 drops. 



It is largely used for a cement, or sticking substance. The Egyptians em- 

 ployed it to suspend their water-colors in painting. 



The commoner qualities are used for giving luster to crape, silk, etc., to 

 stiffen the fibers in cloth-fiuishing, and in calico-printing. For labels, etc., it 

 is usual to mix sugar or glycerine with it to prevent it from cracking. 



The tree has great beauty, and is highly prized in planted grounds where 

 it is able to endure tlie temperature. The wood is hard, and takes a fine 

 polish. Tlie bark of many of the species is highly charged with tannin, 

 and though used in the manufacture of leather, is not a favorite for that 

 purpose, because it imparts a stiff, brittle character to hides during tlie pro- 

 cess of tanning. These barks, however, are largely imported into P^ngland, 

 They are known in commerce as AVattle Barks. 



A species of an allied genus Prosopis (P. juliflora, DC), a native of Texas, 

 yields an inferior gum locally substituted for gum arabic. 



