192 THE AFRICAN RUBBER VINES 



reached the summits of the supportmg trees (over 80 ft.), 

 but he does not give the diameter of the stems. These 

 vmes at Monte-Cafe when seen by Chevaher were twelve 

 and a half years old, and had attained the size of the 

 fully grown vines occurring in the forests of tropical 

 Africa. Two stems which he measured were 18 and 

 20 in. in cncumference at the surface of the soil, and 

 16 in. at a height of 6 ft. ; another measured 18 in. in 

 circumference at 8 in. above the soil, and at 12 in. divided 

 into four branches, each of which was 10 in. in circum- 

 ference. Chevalier states that none of the other species 

 of Landolphia of which he has had the opportunity of 

 measuring specimens of known age shows such rapid 

 growth as these vines of L. Dawei at Monte-Cafe. 



With regard to L. Heudelotii, Henry has expressed 

 the opinion that vines growing under the best conditions 

 in the forests of Casamance or the Ivory Coast can 

 be tapped when about eight years old, whereas in the 

 dry regions of the Sudan the vines are not ready for 

 tapping imtil at least ten j^ears old and the bushes not 

 before the twentieth year. 



Experiments with L. owariensis in the Gold Coast and 

 with L. Kirkii in Nyasaland have shown that both these 

 species grow very slowly under cultivation. 



The growth of the plants is also considerably affected 

 by their environment. As already pointed out, certain 

 species develop into either vines or bushes according as 

 they occur in forest or upon open ground, and the vines 

 are also influenced by the conditions under which they 

 grow in the forest. It has been found that growth is 

 most satisfactory when the vines occur on the outskirts 

 of the forest or in open forest, where they have free access 

 to light and air. In dense forest, on the other hand, the 

 growth is retarded and the stems remam exceedingly 

 thin until the vine has climbed to the top of the support- 

 ing tree and can expose its leaves to the light, after which 

 the stems begin to increase in thickness ; vines growing 

 under these conditions, therefore, develop very slowly. 



The rubber vines also differ considerably in vigour of 

 growth, some of them attaining very large dimensions 

 whilst others remain comparatively small. Wikl speci- 

 mens of L. Klainei and L. Dmvei, two of the most 

 vigorous vines, have been recorded with stems 12 in. 



