PREFACE. 



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. Kendle, 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 Gnetacece. 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 Gnetacece 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 Gymnospermce. The Gnetales, 

 however, exhibit characters that do not wholly conform with the 

 conception of the Gymnospennce which is usually accepted. In 1908 

 Arber and Parkin expressed the opinion that the Gnetales are " gym- 

 nosperms nearly related to angiosperms," derived from a common 

 ancestral stock, the HemiangiospernuB. In 1912 Liguier and Tyson 

 advancerd arguments in favour of the treatment of the Gnetales as 

 an early, highly specialised branch of the Angiosper?nce, 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. 0. Stapf, F.R.S., Keeper of the Herbarium, Kew. The 



