OF THE SIERRA LEONE BOUNDARY COMMISSION. 67 
further into the question. It seems to me that if we take all 
West Tropical Africa from Senegambia to Angola, and the 
whole drainage-area of the Niger and Congo, and if we were to 
exclude all the higher land above 3000 feet in altitude, we should 
have an extremely natural botanical region. The Rubiacew— 
which have been so well worked out by Mr. Hiern in the 
‘Flora of Tropical Africa,’ which include the Welwitschian speci- 
mens and Congo plants in the British Museum—seemed to me 
to be a good order in which to test this theory. I find that of 
the 498 species enumerated :— 
250 are confined to West Tropical Africa ; 
30 in West Tropical Africa, which also occur in Darfur, 
Fazokel, or Schweinfurth’s collections near the water- 
shed of the Congo in Monbuttuland, Niamniam, &c. ; 
76 are confined to Nileland and Abyssinia ; 
58 to Mozambique, Zanzibar, and Zambesi ; 
16 range from Abyssinia to Angola; 
3 Mozambique to Angola; 
20 confined to Angola; and 
18 are common to East and West Tropical Africa, which 
small number includes common widely diffused species. 
That is 250+30, or 56:2 per cent. belong entirely to this 
proposed region, 40°2 per cent. to the remainder of Tropical 
Africa, and 3°6 per cent. do not suit this theory. 
Other points in favour of this view are :— ae 
1. It agrees very closely with one of Wallace’s distribution 
areas (2, Soudan). 
2. It is really an area bounded by water-partings. 
3. It is distinguished by the rainy season being almost in- 
variably between April and November, while on the Eastern 
side it is almost invariably between October and May *. 
4. It is an evergreen-forest region characterized by great 
humidity, and is separated from similar districts on the East 
Coast by a series of grassy upland plateaux and mountains 
which seem to be approximately continuous from Abys- 
sinia to Nyassaland and Angola. _ 
As Mr. ©. B. Clarke has pointed out for similar regions of 
* The rain occurs in Senegambia, Sierra Leone, and Kordofan as above ; 
Unyamwesi, Tanganyika, and Tette (our winter) as above ; Zanzibar has a double 
season, Oct.—Dec. and Mar.-May; while the Gaboon 1s exceptional with rain 
also from Oct. to May, and Abyssinia has summer rains. 
