PREFACE. 7* 



elude the usual or average range of size in the specimens examined by 

 the authors, and which in nature are often departed from according to 

 circumstances favourable or unfavourable to luxuriance, in which the 

 plant may be placed. It may be observed, however, that relative pro- 

 portions often hold good, while absolute size may be widely different. 

 Nor must undue importance be attached to the more prominent and 

 briefly expressed characters made use of in the synoptical tables which 

 are given under each genus of two or more species. These are intended 

 to serve rather as guides in the determination of the species than as 

 absolute or final indications, and must always be checked by a com- 

 parison of the specimen with the more detailed description. 



In citing the several localities for each species, it has appeared ex- 

 pedient to arrange them under six principal geographical regions into 

 which the enormous area embraced by this Flora has been divided.* 

 These are :— 



1. Upper Guinea, including under this term the Western Coast 

 region from the river Senegal on the north to Cape Lopez, imme- 

 diately south of the equator : the interior drained by rivers intermediate 

 between these limits ; and the small islands of the Gulf of Guinea, 

 Fernando Po, Prince's Island, St. Thomas and Annabon. 



2. North Central. The Sahara eastward to the countries watered 

 by the Nile and its tributaries, including also Bornu and Haussa. 



3. Nile L^nd. The area drained by the Nile, extending some three 

 or four degrees south of the equator, so as to include the plants col- 

 lected by Captains Speke and Grant, after leaving the watershed coast- 

 wards on their way from Zanzibar to the Victoria Nyanza. 



4. Lower Guinea. Western tropical Africa, from Cape Lopez 

 southward to the tropic of Capricorn, including Congo, Angola, Ben- 

 guella, aud Mossamedes. 



5. South Central. This includes the upper Zambesi from the 

 Victoria Falls, Lake Ngami, and a vast area as yet unexplored. 



* To the citation of localities, the sign (!) is added whenever a specimen has been actually 

 seen by the author. An asterisk (*) is prefised to those species which are believed to have 

 °ccu introduced. 



