vi PREFACE. 
collections were no longer available for study at Kew, and Professor 
Oliver eventually abandoned the further prosecution of the work. He 
retired from his official post in 1890. 
Meanwhile the publication of the first three volumes had considerably 
stimulated botanical research in Africa. Sir Jobn Kirk had become 
Consul-Qeneral at Zanzibar, and lost no opportunity of encouraging 
collectors. Sir H. H. Johnston, K.C.B., H.M. Commissioner in 
British Central Africa, imitated his example in British Central Africa. 
Much valuable work in Equatorial Africa was also done by the 
missionaries of the Church Missionary Society. The Temperate flora dis- 
covered on Kilimanjaro by the Rev. C. New, who was probably the 
first human being to reach its snow-line, and the collections subsequently 
made by Mr. Joseph Thomson on the mountains of East Equatorial 
Africa confirmed the relationships of the high-level floras of Tropical 
Africa with those of the northern hemisphere on the one hand and of 
the Cape on the other, which were first indicated by Mr. Mann’s 
collections on the Cameroons. These relationships raise theoretical 
questions of the highest interest. The various Delimitation Commissions 
which followed the partition of the continent each yielded botanical 
results of more or less value. And the addition of new territories 
to the Colonies on the West Coast stimulated the desire of their 
Governments for an investigation of their vegetable products. 
The result was that an immense mass of material poured into Kew, 
and, though individual collections were worked out in a series of scattered 
papers, a general demand sprang up in foreign countries, as well as at 
home, for a comprehensive work which would sum up the knowledge 
which had been acquired, with no little expenditure of labour and even 
of life, of the vegetation of Tropical Africa. 
The desire eventually found expression in the following letter :— 
“ FOREIGN OFFICE to RoyaL GARDENS, KEW. 
“ FOREIGN OFFICE, March 21st, 1891, 
“S1r,—I am directed by the Marquis of Salisbury to state to you that 
his attention has been called to the fact that three volumes only of 
the ‘ Flora of Tropical Africa’ have as yet been published, and that 
the want of a complete handbook describing known plants impedes 
their study by Her Majesty’s officers in the different parts of Africa 
which are now being opened up to civilisation. 
"A knowledge of African botany is of great practical value, as was 
proved by the discovery of Sir John Kirk, whilst employed as Her 
Majesty's Agent at Zanzibar, of a plant previously unknown, which 
now supplies annually £200,000 worth of india-rubber to the Zanzibar 
market. So, too, on the West Coast of Africa, the trade consists 
almost entirely of vegetable products some of which have only recently 
been brought to light. 
" Lord Salisbury is of opinion that a proper knowledge of the flora of 
Tropical Africa would do much to aid the development of the territories 
