2 
Ridley .— The Distribution of Plants . 
• 
These three factors have all caused the destruction of large numbers of 
species, which have been replaced by invasions of others usually from the 
nearest lands; but in almost every case of which we have records of any of 
these catastrophes in the plant-world, there have remained survivors of the 
lost floras for a long time in suitable spots. Plants of these which have been 
sometimes modified so as to adapt themselves to the change of condition 
may form a distinct portion of the new flora. 
The first two factors have been in action in one or other part of the 
world more or less continuously, probably from the foundation of the globe, 
and no part of the world has been free from their action, which has been 
repeated usually many times. 
The third factor, human agency, almost certainly commenced to play 
its part in altering the vegetation of the world when the human race began 
its first migrations. The earliest record I know of dates from Neolithic 
times, when the immigrants from the East brought into western Europe 
many of our weeds mixed with their cereals and Flax seeds. But the greater 
effects began to be seen later, about four thousand years ago, and very much 
more extensively and rapidly within the last two hundred years. 
Change of Climate. 
This factor does not seem to have come into play in any part of the 
world, at least to any great extent, in historic tinfes, but we have plenty of 
evidence of its having played a most important part in the past. We have 
had in England, since the first appearance of flowering plants, an extensive 
series of great changes of temperature, from the tropical or subtropical 
climates of the Eocene period to the milder one of the Miocene, to 
a temperate climate broken into by one or more Arctic periods and restored 
again later. Each change was accompanied by a corresponding change in 
the flora, the destruction of the old flora and the invasion of a fresh one. 
In the equatorial regions we have no record of any Ice Age later than 
the Permian period, nor indeed, so far as I have been able to detect, any 
period of a temperate climate, but we have had fluctuations of humidity and 
dryness, alternations of a xerophytic period and of a hot, wet period, the latter 
causing the disappearance of the xerophytic flora except in a few still more 
or less dry spots on the higher mountains and on the sea-shore. Such 
island refuges of an otherwise lost xerophytic flora in the Malay Peninsula 
are the plateau of Gunong Tahan, 5,000 to 7,000 feet alt., where nearly all 
the plants are endemic, and the curious sandstone dyke, 1,400 feet high and 
only a few feet across in parts, which traverses the valley of the Klang 
river and is known as Klang Gates. Here, surrounded by mountains even 
higher and lowland jungle of entirely rain-forest species, I found several 
xerophytic endemic plants mixed with characteristic xerophytic plants 
occurring also on the dry mountain areas, very many miles away. 
