30 THE PRINCIPAL RUBBER-YIELDIXG PLANTS 



common outside the tropics, and some of the temperate 

 species produce latex, which, however, does not yield 

 rubber. The production of rubber-yielding latex is 

 therefore restricted to the tropical species, but it must 

 not be assumed that all tropical plants containmg latex 

 will furnish rubber. As a matter of fact only compara- 

 tively few of the laticiferous plants which occur in 

 the tropics yield rubber of good quality, and in dealing 

 with a laticiferous plant, the identity of which is not kno^^'ll, 

 it is necessary to coagulate a quantity of the latex m 

 order to determine the natm-e of the product before 

 decidmg that it is a rubber-yielding species. Many 

 examples might be given of closely allied plants, such as 

 Funtumia elastica and Funtumia africana, which each 

 contain latex and are found gi'owmg in the same situations, 

 but whereas the former furnishes rubber of excellent 

 quality, the latter only gives a sticky resmous product 

 of no commercial value. It is therefore necessary to 

 discrimmate carefully in many cases between closely 

 related species of the same genus, some of which yield 

 good rubber whUst the others furnish a worthless 

 product. 



The rubber-yielding plants include trees, climbers or 

 vines, shrubs and herbs. In America the principal 

 sources of rubber are trees belonging to the genera Hevea, 

 iManihot, Castilloa, Sapium, Hancornia, and Micrandra, 

 the rubber vines being represented by two species of 

 the genus Forsteronia and the shrubs by the Guayule 

 rubber plant of Mexico. In Africa, on the other hand, 

 the majority of the indigenous rubber plants are 

 vines or shrubs belonging chiefly to the genera Lan- 

 dolphia. Clitandra, Carpodinus, and Cryptostegia, and 

 the rubber trees are restricted to Funtumia elastica and 

 a few species of Mascarenhasia, Ficus, and Euphorbia ; 

 herbaceous rubber plants are also represented in Africa 

 by the species of Raphionacme (principally R. utilis, 

 Brown and Stapf) which contain rubber in their tuberous 

 roots. Similarly rubber vines belonging to the genera 

 Urceola, Willughbeia, Parameria, Ecdj'santhera, Chone- 

 morpha, Rhynchodia, Cryptostegia, etc., are abundant in 

 Asia, and the principal rubber trees are Ficus elastica, 

 Dyera costulata, and Bleekrodea tonkinensis. 



The following account enumerates the principal rubber- 



