CH. XVII AFZELIA BIJUGA - 171 



inland trees usually sinking, whilst those of the coast trees usually 

 float, and often for a period of months. 



A glance at the distribution of the genus will enable us to 

 appreciate some of the points that will be touched upon in the 

 following discussion ; and it may he here remarked that the 

 explanation of the distribution of these Leguminous trees will go 

 far to make clear some of the most difficult points in plant- 

 geography. Of the eleven species enumerated in the Index 

 Keivensis, five belong to tropical Africa, occurring on both the 

 east and west coasts as well as in the interior, three are confined 

 to the mainland of tropical Asia, and two are peculiar to Malaya. 

 In the last place we have the wide-ranging Afzelia bijuga, which, 

 if it does not actually occur on the east coast of Africa, is found at 

 all events in Madagascar and in the Seychelles, and is to be 

 followed by the way of the Chagos Archipelago to the Malayan 

 Islands and Queensland, and eastward to Fiji and Samoa. 



The most suggestive feature in the distribution of the genus is 

 to be seen in the frequent station of the species by rivers. We 

 learn from Oliver's Flora of Tropical Africa that these trees find a 

 home along river-courses on both sides of the continent, as on the 

 banks of the Congo, the Niger, the rivers of Senegambia, and the 

 Zambesi, the Zambesi species being found also on the shores of 

 Lake Nyassa. Since tropical Africa possesses about half of the 

 species, it would seem highly probable that it is the home of the 

 genus, and that from the rain-forests in the heart of the continent 

 rivers flowing east and west have borne the buoyant seeds of the 

 wandering species to the coasts of the Atlantic and Pacific Oceans, 

 The operation that I witnessed on a miniature scale in the case 

 of a species of Entada (E. scandens) in the Isthmus of Panama, as 

 described in a later page of this chapter, has been in progress 

 through the ages with the genus of Afzelia in the breadth of the 

 African continent. According to the principle illustrated by 

 Afzelia bijuga in the forests of Fiji, the seeds of the African forest- 

 trees would, as a rule, possess no floating power ; but now and 

 then in the lapse of long periods of time buoyancy in some species 

 would be developed, and such species would ultimately, through 

 their buoyant seeds, find their station along the lower courses of 

 the rivers. 



To sustain this view it is not necessary that continuous rain- 

 forests should now clothe the elevated regions in the interior of 

 tropical Africa ; but it is requisite that there should be sometimes a 

 generic similarity between the plants of the East African and West 



