PREFACE. 
—_—~~e 
It was found necessary in 1904, for reasons then explained by the 
editor, to divide Volume IV. of the “ Flora of Tropical Africa ”’ into 
two sections. The same expedient has had to be adopted in the 
case of the present volume. 
The preparation of two-fifths of this final section of Volume VI. 
has been due to the kind collaboration of Dr. A. B. Rendle, F.R.S., 
Keeper of Botany, British Museum. Members of the Kew staff have 
supplied the rest of the text, with the exception of the account of 
the Gnetaceew. A melancholy interest attaches to that account ; 
it is one of the last contributions to botanical knowledge made by 
its gifted author, the late Professor H. H. W. Pearson, F.R.S., of 
Cape Town, who had bestowed especial attention on this group of 
plants. 
The results of recent study have created a difficulty with regard 
to the position the G'netacee should occupy in a conspectus of natural 
orders. In other floras of the series to which this work belongs, 
that order, which includes the living representatives of the class 
Gnetales, has been placed among the Gymnosperme. The Gnetales, 
however, exhibit characters that do not wholly conform with the 
conception of the Gymnosperme which is usually accepted. In 1908 
Arber and Parkin expressed the opimion that the Gnetales are “ gym- 
nosperms nearly related to angiosperms,” derived from a common 
ancestral stock, the Hemiangiosperme. In 1912 Lignier and Tyson 
advanced arguments in favour of the treatment of the Gnetales as 
an early, highly specialised branch of the Angiosperme, which has 
retained many features inherited from pre-angiospermous ancestors. 
The attempt to resolve this and other cognate difficulties has 
been materially assisted by the valuable advice and practical help 
of Dr. O. Stapf, F.R.S., Keeper of the Herbarium, Kew. The 
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