BOTANY. 423 
region, manifesting its greatest diversity of form, and its purest. 
types on the Malay islands, especially on Java and Sumatra, 
where its proper centre lies. But one species passes its bounda- 
ries toward the west, and plays an important part around the 
Mediterranean, and three species are found in America, whilst the 
typical genus is found exclusively on the Malay islands, where 
only a few species of chestnut-oak are found, and not a single true 
oak. Ina similar manner the oak group occurs chiefly in Amer- 
ica, north of the equator, forming a second centre of distribution 
in the mountains of Mexico, where it manifests not only more 
numerous species but also greater diversity of organization, than 
anywhere else, several large subdivisions being found that are not 
met with elsewhere, whilst chestnuts and beeches are entirely 
wanting. Although the beech group exhibits such a preponder- 
ance of species in Chili, that that country must be regarded as its 
proper home, still the species are so scattered that it is difficult, 
with the present distribution of land and water, to refer all to a 
single centre. This difficulty is not so great, however, in regard 
to Nothofagus, which occurs in New Zealand and Van Dieman’s 
Land, since there are other grounds for assuming that these were 
at one period connected with Chili. Still it seems impossible to 
refer the species of Fagus to the same centre, since the nearest 
related species is separated by 70° of latitude from the beeches of 
the south, so that, paradoxical as it may appear, Japan seems once 
to have formed the connection between the beeches of the north 
and south, just as we find points of contact between Chili and 
Japan in other respects. An explanation of this is afforded by 
the fact that the beeches of Japan conform to those of the Miocene 
epoch ; the centre of distribution of the typical beeches must there- 
fore be sought in a past geological period, and from it they must 
have been dispersed in different directions, before the present dis- 
tribution of land and water. Besides the three principal centres 
alluded to, there are also three secondary centres of distribution 
characterized by peculiar genera and sub-genera. The principal 
groups in passing beyond their respective regions, and mingling 
with each other have produced regions of transition, in which forms 
appear which are the connecting links between the types from the 
different centres. Various facts in regard to the distribution of 
Plants in general are also peculiarly illustrated by this family. 
Thus it exhibits most clearly the marked difference between the 
