250 ECONOMIC BOTANY. 



are about seven per cent, of volatile-oil, fifty per cent, of 

 resin, some gum, and various impurities. Its use in medi- 

 cine is as a mild counter-irritant. 



215. Gum-Ammoniacum exudes as a milky juice 

 from Dorema ammoniacum, a plant belonging, like the two 

 preceding, to the family Utnbelliferce. It grows on the 

 steppes of Asia along with the Asafcetida-plant, Scorodosma 

 fcetidum. It is a fennel-like plant, with large compound 

 leaves, and attains a height of six or seven feet. The 

 juice exudes spontaneously (probably upon the puncture of 

 insects). It hardens in grains or lumps. It is whitish, 

 has a waxy lustre, and is not entirely opaque. It softens 

 in the hands. The odor is strong and peculiar, and the 

 taste bitter. The gum contains about seventy per cent, of 

 resin, three or four per ceut. of volatile-oil, and some gum 

 and water. It is used in the manufacture of cement, also 

 in medicine as a stimulant. 



216. The Turpentine of commerce comes mainly from 

 Europe and North America. In the former country the 

 species Abies exeelsa, Ah. pectinata, Pinus maritima, P. 

 Laricio, P. silvestris, and Larix JEuropcea yield this oleo- 

 resinous substance. In North America it is obtained from 

 the Balsam-Fir (Abies balsamea), White Pine {Pinus 

 Strobua), Ked Pine (P. resinosa), Loblolly or Old-field 

 Pine (P. Tceda), and Broom Pine (P. palustris). Turpen- 

 tine is found both in the cortex and in the young wood ; 

 essentially the same methods are employed in the difierent 

 countries in obtaining it. With an axe, or similar instru- 

 ment, wounds or cavities of considerable size are made, or 

 holes are bored with augers, into the trunk of the tree, and 

 in these the turpentine collects. The better kinds are thin 

 and clear, and those of poorer quality are thick and cloudy, 



