560 Ridley . — On Endemism and the Mutation Theory . 
going on as late as 1900 (see Brown’s article on the Forests in the Appendix 
to Trimen’s Flora). A very large proportion of the species in the Malay 
region are epiphytes, especially Orchids. These are the first to disappear 
when timber is felled and the country exposed to the sun. The very small 
number in the plain districts of India illustrates this. In Ceylon there are 
only eighty species against over 130 in Singapore island alone. 
The Mutation Theory. 
The theory of the evolution of species by Natural Selection is, as 
I understand it, as follows : 
An organism produces forms which in various ways are not identical 
with the parent form. These forms are known as varieties or mutations. 
Should any of these forms be adapted in any way so as to be more 
suitable for the surrounding conditions than the parent form, they may 
persist and reproduce themselves in the mutation form. The mutations 
do not necessarily reproduce their replica, but may revert to the original 
form. If, however, selection comes into play and the mutation is con- 
tinually selected, the form becomes a fixed mutation. I shall give instances 
in the case of Antigonon and other plants. 
Should the forms connecting the fixed mutation with the original form 
disappear, and the alterations be sufficiently distinct and important to 
warrant it, we call the new form a species. 
For a mutation to become a fixed one it is necessary that it should be 
able to reproduce itself successfully and continuously. 
In most or more probably in all cases of successful fixed mutations the 
determining factor is the surrounding conditions environing the original 
plant. Thus a plant adapted for the dense shade of the forest may dissemi- 
nate its seed nearer the edge where the light is greater. Here natural 
selection comes into play, and the mutations more adapted for greater light 
will grow and reproduce along the edge. If the forest be near the sea, the 
mutations gradually getting nearer and more adapted for sandier and 
sandier spots may in time be so selected that they take on a maritime form. 
This form in time becomes so far adapted to a littoral life that it cannot 
revert to the jungle form, and remains as a species. 
This is only one sample of the evolution by Natural Selection ; 
others are connected with adaptations for climate, fertilization, dissemi- 
nation, &c., the object being that an organism can by mutating fill up 
a space, or state of conditions, which in its original form it cannot do. 
This theory accounts for the great number of species in the world 
and their adaptation to their surroundings and conditions of life, and 
can be tested and proved by a study of mutations. No other theory 
has been produced which can account for the facts. * 
