INTRODUCTION AND APPENDIX. lxv 
or near the equator. If, as has with much probability been surmised, the existing types 
of vegetation originated in northern latitudes and by migration southwards, and by 
differentiation and dispersion, peopled the southern hemisphere, there is no obvious 
obstacle to the prolongation of these two particular types (and many others) into South 
America, New Guinea, and Australia. But there is this difference between the oaks of 
the tropics of the Old World and those of the New, that the Asiatic in their prolongation 
southward to Malacca and thence eastward to Borneo in descending to the sea-level 
assume different types of structure from their northern allies, forming distinctly tropical 
sections of the genus, as Cyclobalanus, Chlamidobalanus, Lepidobalanus, and Castanopsis. 
On the other hand, the tropical-American oaks where they descend to the sea-level do 
not assume a character sectionally differing from temperate-American species. It is 
startling to have to regard the genus Quercus as tropical rather than temperate; but so 
it is, and especially in India, where about 70 species are purely tropical and only 12 
purely temperate. 
Turning now to the concluding pages of Mr. Hemsley’s Introduction (pp. xxxix-Ixi), 
which are devoted to an exposition of the primary botanical regions of the globe, I 
find that these regions are based upon far more complete and reliable data than had 
previously been available. In the last paragraph but one Mr. Hemsley remarks that 
I do not share some of the opinions which he has expressed in his previous pages. This 
remark must not be taken as conveying the impression that I dispute either his facts or 
methods. I shall now, in preference to discussing either, give in outline my own idea 
of the principal botanical regions of the globe, from which it will be seen how far I 
differ from him in the limitation of the primary Floras of the globe. 
I limit the primary botanical regions of the globe to two, the Tropical and the 
Temperate ; these are distinguished by both climatic and botanical features—tropical- 
country plants will not, as a rule, bear a temperate climate, nor temperate-country 
plants a tropical climate. Botanically the two regions are distinguished by the restric- 
tion of certain natural orders to one or the other, and the prevalence of others in one 
or the other. The geographical limit between these Floras in either hemisphere varies 
with every few degrees of longitude, being affected by elevation of surface and local 
climatal conditions. I do not distinguish the northern and southern Frigid Floras as 
primary regions separate from the Temperate, for these regions contain no genera and 
very few species different from the Temperate, and the geographical limits of any group 
of species that may be selected as inhabiting the coldest region of the globe are unde- 
finable by latitude or by isothermal or isotheral lines. 
If a distinctive name is desirable for the two primary regions, I would suggest that 
of Botanical Empires. 
The regions next in importance to the two primary are in my view seven,—two 
north temperate, of the Eastern or Old and Western or New World respectively ; two 
tropical, corresponding to the above; and three south temperate (America, Africa, and 
BIOL. CENTR.-AMER., Bot. Vol. I., October 1888. i 
