PREFACE. 
Tuts is the last section of the “ Flora of Tropical Africa” which will 
be issued under my editorship. The control and supervision necessary 
in an undertaking of the kind cannot be properly exercised except 
the headquarters of its preparation. Some degree of uniformity must 
at least be aimed at in the work of different contributors. Questions 
will consequently arise on which the editor must give a decision: 
difficulties which are readily solved by personal discussion are not 
disposed of so easily by correspondence. 
The preparation of this section has been protracted. When I retired 
from the Directorship of Kew in 1905 much of the material available 
had been worked up by my indefatigable contributor, Mr. J. G. 
Baker, F.R.S. The continuous access of fresh collections had in the 
meantime largely added to it. In fact the general position with regard 
to the Flora resembles the “Curve of Pursuit,” in which the pursuer 
has to change his direction constantly in the attempt to overtake his 
elusive quarry. In the case of the smaller orders Mr. Baker's advanced 
years made it necessary to entrust the necessary additions to other 
hands. The Huphorbiacee were not so easily disposed of. This vast 
family will probably prove to supply the dominant constituent of tropical 
forests. In view of the large access of fresh materia] and of what had 
been worked out by Continental botanists it was necessary to recast 
entirely what had been prepared. This task was generously undertaken 
by my successor Lt.-Col. Sir David Prain, F.R.S., and though my 
name stands on the title-page of the volume, its accomplishment and the 
merit which attaches to it must for the most part be attributed to his 
indefatigable energy and critical insight. Mr. J. Hutchinson collabo- 
rated with him, and Mr. N. E. Brown, A.L.S., who finds a peculiar 
fascination in the study of succulent plants, the difficulties of which 
most botanists find deterrent, undertook the genus Huphorbia. 
The present section thus disposes of all that was in view when I 
retired from Kew. The “ Flora of Tropical Africa ” differs from other 
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