Ridley. — On Endemism and the Mutation Theory. 557 
Alterations of the Flora due to Cltmatic Changes. 
A comparatively small change of climate may very easily cause 
the destruction of species on a large scale : (1) by actual destruction 
of species ; (2) by allowing the development of an entirely fresh flora 
which would swamp the indigenous flora. 
A diminution of the rainfall, for instance, due to excessive destruction 
of trees, could entirely destroy the epiphytic flora of a region. I have 
shown how on a small scale in the Mangrove swamps at Kranji in Singa- 
pore, and the felling of the jungle on the slopes of Bukit Timah, the light 
and heat let in destroyed the epiphytic flora and herbaceous plants in 
these forests. 
I have another instance of such destruction. Some years ago, 1905, in 
Singapore, we had an extraordinarily dry and hot spell which lasted for 
a month or two, during which period the epiphytic Fern Polypodium 
sinuosum , of which there was a great abundance on some of the trees, 
was completely dried up, and almost every plant of it in the gardens 
utterly perished, and no young plants of it ever came up again on these 
trees. 
At present we have very little information, at least collected together, of 
modification of climate and consequently of floras in a natural condition of 
things, and alterations due directly or indirectly to the action of man. These 
are subjects well worthy the study of naturalists. Changes of climate have 
occurred without any geologic cataclysm in past years we know, e. g. the 
glacial period of Europe, and I understand the desert period of the south of 
England. In Nicol’s ‘ Three Voyages of a Naturalist ’, chap, iv, ^describing 
South Trinidad, he notices great numbers of standing and fallen trees 
apparently dead for many years covering the whole island, and the dis- 
appearance too of the goats which formerly inhabited it. There is no clue 
as to the cause of the destruction or its date, and he considers it improbable 
that it was caused by volcanic action, as at the summit trees and tree-ferns 
still flourish, and there are no traces of fire. However, as it is a volcanic 
island, the destruction might have been caused by the emission of the 
poisonous gases or water, as was reported to me as occurring in the Hawaii 
islands some years ago. 
That floras do change without human interference we know from 
Clement Reid’s researches into the early floras of Britain and Holland, 
species entirely disappearing and being replaced by others, but from what 
causes we are still ignorant. There is no evidence whatever to show 
geological cataclysms in all such cases. The process may be and probably 
is slow at most periods. 
