VI PREFACE. 



circumstance that in the Gnetacece the character of " nakedness of 

 the ovuJe " is manifest, admits the formal retention of the order in 

 the GymnospermcB, and allows the accordance to it, in our ordinal 

 conspectus, of a serial position which conforms with the practice 

 adopted in other floras of the series in which the " Flora of Tropical 

 Africa " finds a place. In the definition of the Gnetales, prepared 

 for this conspectus by Dr. Stapf, due allowance is, however, made for 

 the peculiar and ambiguous position of the class. The terminology 

 employed in describing the organs of reproduction is intended to 

 reflect our belief that, in spite of the nakedness of the ovule, the 

 affinities of the Gnetales are with the angiospermous rather than with 

 the gymnospermous phylum. 



Associated with this difficulty as to the position of the Gnetales 

 is the more serious one created by the modern view as to the relation- 

 ship which these two great phyla bear to each other. The phe- 

 nomenon of gymnospermy, first pointed out by K. Brown in 1826, 

 was turned to taxonomic account by Brongniart as early as 1828. 

 But when Brongniart recognised in the Gymnospermce a distinct 

 natural group, he regarded that group as an integral part of the 

 Dicotyledones. It was not until 1864 that A. Braun proposed the 

 treatment of the Gymnosfermce as a division of the Phanerogamcc 

 equal in status to the Dicotyledones and the Monocotyledones taken 

 in conjunction. The evidence in favour of the view, adopted by 

 Hooker in 1876, that the two primary phanerogamous divisions, 

 AncjiosfermcB and Gyynnospermce, represent quite distinct lines of 

 evolution, is so strong that this disposition is now generally accepted. 



The series of Colonial Floras was initiated in 1859, and the first 

 work in this series was issued in 1861, while the view expressed by 

 Brongniart in 1828 was still generally accepted. In that flora the 

 Gymnospermxp were accordingly regarded as a subclass of the Dicoty- 

 ledones, and were assigned a serial position immediately after the 

 really dicotyledonous subclasses and immediately before the mono- 

 cotyledonous ones. The view that the Gymnospermce are a subclass 

 of the Dicotyledones has not been maintained in every Colonial 

 Flora completed since 1861. In one instance the Gy^nnospermcr 

 have been regarded as a group, within the Dicotyledones, equal in 

 status to the whole of the angiospermous subclasses of that class. 

 In other cases the Gymnospermce have been advanced to the rank 

 of a distinct class, comparable in status with the Monocotyledones 

 on the one hand, the Dicotyledones on the other. Neither of these 

 two modifications of the original view necessitates a change in the 



