INTRODUCTION. 
AS stated in the Preface, this work was undertaken mainly in the interests of Geogra- 
phical Botany; and the distribution of the plants enumerated therein has been tabulated 
and discussed in considerable detail in the ‘‘ Appendix ” contained in the fourth volume. 
The completion, or approaching completion, of several important works on systematic 
botany, dealing with the vegetation of large areas, such as Boissier’s ‘ Flora Orientalis,’ 
Hooker’s ‘Flora of British India,’ Gray’s ‘Synoptical Flora of North America,’ and 
monographs of large Natural Orders, together with recent botanical explorations in 
China, Madagascar, the mountains of Tropical Africa, and elsewhere, affords materials 
for a wider survey of the distribution of plants than has hitherto been attempted, and 
a closer comparison of the primary botanical and zoological regions of the world. To 
do this exhaustively would, of course, occupy much time and fill a large book; therefore 
only an exposition and rapid review of the principal facts will be attempted here *, and 
the inquiry will be limited to flowering plants. 
Before approaching the examination of the botanical regions themselves it seems 
desirable to produce some further statistics and then endeavour to estimate their 
relative value yf. 
Throughout this work the classification and generic limits of Bentham and Hooker's 
‘Genera Plantarum’ have been followed, and all comparisons are made on the same, or 
practically the same, basis. Since the appearance of the first part of the ‘Genera 
Plantarum’ in 1862, very numerous new plants have been discovered, including some 
extremely singular and anomalous ones, though none probably to which the authors 
would have assigned the rank of a new natural order. The number of distinct genera 
and species has, however, been largely augmented. Elsewhere { some particulars have 
been given of the subsequent additions to the Composite, but it is unnecessary to enter 
into similar details respecting all the natural orders. Nevertheless, for purposes of 
comparison, it will be convenient to give here some of the statistics and rough approxi- 
mations arrived at in the ‘Genera Plantarum’ §. 
* The questions discussed in the following pages might more appropriately have been incorporated in the 
“ Appendix ;” but this is a further development of the subject suggested by Sir Joseph Hooker after perusing 
the analysis of the Flora of Mexico. 
+ Following the most approved nomenclature, the primary geographical divisions of the vegetation of 
the world are designated “ regions” and the secondary divisions “ subregions.” 
+ Vol. IV. p. 249. 
§ From a summary by N. E. Brown in the ‘ Gardener’s Chronicle,’ n. s. xix. p. 733. 
BIOL. CENTR.-AMER., Bot. Vol. I., October 1888. b 
