212 TROPICAL AGRICULTURE 



This gum is also known as Acacia, Turkey, Senegal, India, 

 and Barbary gum. In obtaining gum arabic strips of bark are 

 removed from the tree and the gum is collected from the 

 wounds after about 60 days. Gum arabic is used extensively in 

 pharmacies in preparing pills and for holding in suspension 

 substances which are insoluble in water. 



Gum tragacanth is a gummy exudation of Astragalus gum- 

 mifer and other species of related plants from Syria, Armenia, 

 Kurdistan, and Persia. In harvesting this gum the plants 

 are incised and the gums collected in white or yellow sheets. 

 Gum tragacanth is used for the same purpose as gum arabic, 

 but is less soluble. 



Mastic resin is obtained from a small tree (Pistacia lenticus) 

 of the Mediterranean region. The gum is obtained from trans- 

 verse incisions in bark and is obtained about 3 weeks after 

 tapping. The trees are tapped 3 or 4 times during the season 

 from June to September. The annual yield per tree is 8 to 10 

 pounds. The resin occurs in masses of a pale yellow color. 

 It is brittle and melts at 108° C. Mastic was once much used 

 in stomach debilities and for fine varnishes, but is being re- 

 placed by other resins. 



Guaiacum resin is obtained from West Indian trees (G. offi- 

 cinale and G. sanctiim). The resin occurs either as a natural 

 exudation or is obtained by cutting the tree into sections and 

 boring holes in the wood or by building fires under each end 

 of the log and driving the resin out by heat. Guaiacum is 

 widely used as a chemical indicator, being a very sensitive re- 

 agent for oxidizing substances. It is also used in medicine 

 as a stimulant and alterative. 



Tacamahaca resin is obtained from a Venezuelan tree {Bur- 

 sera tomentosa). The resin contains considerable volatile oil. 

 In the East Indies another kind of Tacamahaca resin is ob- 

 tained from Calophyllum inophyllum. The resin is perhaps 

 very similar to those of turpentine and is used in making plas- 

 ters and ointments. 



