THE PRINCIPAL RUBBER-YIELDING PLANTS 33 



British Guiana and experiments have been made to de- 

 termine the jdeld of rubber from forest trees. Interesting 

 results have been obtained from tappmg experiments 

 conducted during a period of two years on old trees 

 growing on the river bank at the Bonasika Reserve. 

 The average yield of rubber dm-uig this period was 

 18-33 oz. per tree, but it was found that whereas the 

 rubber obtamed from the first tappings was of excellent 

 quaUty, the product from the later tappmgs was soft and 

 tacky. This point is of considerable importance as it 

 affects the value of the tree for planting pm-poses. The 

 results so far obtained from young plantation trees have 

 been disappointing, and it seems doubtful whether Sapium 

 Jenmani can be recommended for cultivation in British 

 Guiana. 



Further details regardmg the rubber of S. Jenmani 

 will be found in the Imperial Institute Selected Reports 

 on Rubber and Gutta Percha, pp. 280-4.* 



4. Micrandra siphonioides, Benth. 



The genus ]\Iicrandra is very closely related to Hevea, 

 but is distinguished from it by its undivided leaves and 

 its smaller capsules and seeds. The best known of the 

 Brazilian species is Micrandra siphonioides, a large tree 

 growing in the Rio Negro area, which accordmg to Ule 

 yields good rubber. The tree is, however, not exploited 

 to any extent by the natives, as its latex camiot be mixed 

 with that of the species of Hevea growing in the same 

 district. It is stated, however, that rubber is prepared 

 from species of Micrandra on the Putumayo and Ucayali 

 rivers. 



5. Euphorbia spp. 



Most of the tropical species of Euphorbia yield latex 

 freely, but the product which the latter furnishes on 

 coagulation is usually of resinous character and becomes 

 hard and brittle on keeping. 



The most important species of Euphorbia as sources 

 of rubber or rubber-like material are Euphorbia Intisy, 

 Dr. d. Cast., which furnishes the Intisy rubber of southern 

 Madagascar ; Euphorbia rhipsaloides, Welw., a native 

 of Angola, from which the resinous product known as 

 " ahneidina " or " potato gum " is derived ; Euphorbia 

 Tirucalli, L., which has been recently exploited in Natal ; 



* Colonial Reports — Miscellaneous, No. 82. Wyman & Sons, Ltd. 



