34 THE PRINCIPAL RUBBER- YIELDING PLANTS 



and Euphorbia fulva, Stapf, the Palo Amarillo tree of 

 Mexico. 



A large number of spechnens of the products obtained in 

 South Africa from the latex of species of Euphorbia have 

 been exammed at the Imperial Institute, and several 

 typical analyses are given in Selected Rej^orts on Rubber 

 and Gutta Perchu, pp. 416-21. The results show that 

 the resin in the dry material may range from 50" 1 to 928 

 per cent., and the caoutchouc, which is usually of inferior 

 quality, from 67 to 32 1 per cent. 



A specimen of the product stated to be derived from 

 the latex of Euphorbia Tirucalli in Natal was found on 

 analysis at the Imperial Institute to have the following 

 composition : 



This product from Eujyhorbia TiriicalU is utilised, like 

 " almeidina," for mixing purposes m rubber manufacture. 



II. URTICAGEAE 



6. Castilloa elastica, Cerv., the Central American rubber 

 tree. 



The habitat of this tree includes southern Mexico, 

 Central America, some of the West Indian islands, 

 Colombia, and the western slopes of the Andes in Ecuador 

 and Peru. Large CastiUoa plantations have been estab- 

 lished in Mexico, and the cultivation of the trees has also 

 been undertaken on a smaller scale in some of the States 

 of Central and South America, and in tlie West Indies, 

 particularly in Trinidad and Tobago. Tlie tree has also 

 been introduced into Africa and Asia, but it has not 

 given very good results when cultivated outside Central 

 and South America. 



