RUBBER 



409 



There are said to be over $400,000,000 invested in rubber plantations 

 and they supply (1919) about 83 per cent of the total world's require- 

 ments. 



The trees in plantation are planted about 150 trees per acre (20X15 

 ft.) and do not become productive until four to seven years of age, when 

 they are 5 to 7 in. in diameter at breast height. If tapped before this 

 age the rubber yield is inferior. At seven years of age, the annual yield 

 is only about \ Ib. per tree per annum. The average at twelve to fifteen 

 years of age is about i^ Ib. per tree. 



At first all the brush and weeds were removed from an area to be 

 planted at great expense, but it was found that the hot t-opical sun 





Copyright by U. 5. Xubbtr Company. 



FIG. 1 10 . Close view of tapping methods and cups used in collecting the latex. 



baked out the soil too readily and until the plants reached a size sufficient 

 to shade the soil, it was necessary to grow some leguminous plants to 

 both shade and enrich the soil. 



The methods of tapping and reducing the latex have been greatly 

 improved over the systems in vogue with wild rubber, although it cannot 

 be said that they have reached a finality of development. A common 

 method is to make a series of V-shaped incisions on four sides of the tree 

 up to a height of 5 to 7 ft. from the ground. The latex is collected in a 

 cup hung at the apex of each V. The " herring-bone " plan with a ver- 

 tical incision and lateral channels on either side is used as well as the spiral 



