THE AFRICAN RUBBER VINES 197 



tion in this way leads, however, to the inevitable destruc- 

 tion of the plants. In the case of tlie species with 

 rhizomes, sufficient of the underground stems are usually 

 left in the ground to ensure the production of new plants ; 

 but there is a considerable danger of their extinction 

 if the process is extensively worked by the natives. 



A number of machines have been designed for the 

 extraction of rubber from bark by mechanical processes, 

 analogous to those employed by the natives, and some 

 of them give very satisfactory results so far as the yield 

 and quality of the rubber are concerned. Very large 

 supplies of bark are, however, required in order to run an 

 mstallation of these machines for any length of time. 

 The Guiguet and the Valour machines are the two 

 prhicipal types in use at the present time, and installa- 

 tions of each of these have been tried in different parts 

 of Africa. Such machines can, of course, be used to 

 treat any suitable bark containing a sufficient amount of 

 rubber, and not merely the bark of Landolphia stems. 



Yields of Rubber from the Vines. — In considering the 

 recorded yields of rubber from the African vines, it will 

 be convenient to consider the different species separately. 



Landolphia Heudelotii. — Chevalier made a careful study 

 of this vine in the French Sudan, and estimated from 

 his experiments in that country, which has a dry climate, 

 that the average yield of dry rubber from a vine which 

 had been previously tapped was about 50 grams per 

 annum, the vine being tapped twice during the year. 



In the moister districts, such as Casamance and the 

 Ivory Coast, the yield of rubber is greater than in the 

 Sudan. Experiments by Teissonnier gave the followmg 

 results : 



L. Heudelotii bushes 



,, vmes 



Similarly, a series of experiments was conducted at 



Mangacounda in Casamance by Maury on eight L. 



Heudelotii vines, the oldest of which was stated to be 



