temperate Europe and America, and in the barren north-polar regions.
But there is another set of facts, which help us on another step towards the
case of the Javanese mountain flora. On the higher slopes of the Himalayas, on
the tops of the mountains of Central India and of Abyssinia, a number of plants
occur which, though not identical with those of European mountains, belong to
the same genera, and are said by botanists to represent them; and most of these
could not exist in the warm intervening plains. Mr. Darwin believes that this
class of facts can be explained in the same way; for, during the greatest severity
of the glacial epoch, temperate forms of plants will have extended to the
confines of the tropics, and on its departure, will have retreated up these
southern mountains, as well as northward to the plains and hills of Europe. But
in this case, the time elapsed, and the great change of conditions, have allowed
many of these plants to become so modified that we now consider them to be
distinct species. A variety of other facts of a similar nature have led him to
believe that the depression of temperature was at one time sufficient to allow a
few north-temperate plants to cross the Equator (by the most elevated routes)
and to reach the Antarctic regions, where they are now found. The evidence on
which this belief rests will be found in the latter part of CHAPTER II. of the
"Origin of Species"; and, accepting it for the present as an hypothesis, it enables
us to account for the presence of a flora of European type on the volcanoes of
Java.
It will, however, naturally be objected that there is a wide expanse of sea
between Java and the continent, which would have effectually prevented the
immigration of temperate forms of plants during the glacial epoch. This would
undoubtedly be a fatal objection, were there not abundant evidence to show that
Java has been formerly connected with Asia, and that the union must have
occurred at about the epoch required. The most striking proof of such a junction
is, that the great Mammalia of Java, the rhinoceros, the tiger, and the Banteng or
wild ox, occur also in Siam and Burmah, and these would certainly not have
been introduced by man. The Javanese peacock and several other birds are also
common to these two countries; but, in the majority of cases, the species are
distinct, though closely allied, indicating that a considerable time (required for
such modification) has elapsed since the separation, while it has not been so long
as to cause an entire change. Now this exactly corresponds with the time we
should require since the temperate forms of plants entered Java. These are now
almost distinct species, but the changed conditions under which they are now
forced to exist, and the probability of some of them having since died out on the
continent of India, sufficiently accounts for the Javanese species being different.