270 A TEXTBOOK OF GENERAL BOTANY 
can be answered by a hypothetical example. We will start with 
a very ancient and simple plant which we will call 4. We will 
suppose that this plant gave rise to two different forms, B and 
C, which were naturally very much like their parent 4. B and C 
were better fitted to their environment than 4, and in the course 
of time 4 died out and disappeared, while B and C both survived. 
B was very thoroughly adapted to its environment, and it con- 
tinued to exist through long ages and is a component of our 
present flora. C was either less fitted for its environment or for 
some other reason underwent further evolution and gave rise 
to form D, which in turn produced £, etc. As a descendant of 
E we have a living form, XY, which is very different indeed from 
the parent form A and very much more complex. Now the rela- 
tionship between XY and B is clear. X is not a descendant of B, 
and B is very clearly not a descendant of X. Y is, however, 
a descendant of A, which was very similar to B, so that we can 
say that, while XY is not a descendant of B, it is a descendant of 
a form very similar to B. It seems very improbable that there still 
exist many, if any, of the forms of plants which were the direct 
ancestors of modern flowering plants, but it appears certain that 
many living forms are very similar to certain ancestral stages. 
It does not follow that because a plant has a simple structure 
it is at a disadvantage as compared with more complex plants. 
Just as many trees are fitted for growing in the open, so many 
mosses are fitted for growing on trees, and many one-celled 
plants for floating in water. 
Evolution and modern thought. ‘The doctrine of organic evolu- 
tion has come to be universally accepted by scientists, and it 
is not too much to say that it is the corner stone of modern 
biological science. The entire classification of plants and animals 
is based on the doctrine of evolution, while structures, functions, 
and activities are explained in the light of evolution. 
In the past there has been considerable misunderstanding of 
the teaching of evolution, and consequently prejudice against 
it. Theories of evolution date back to the ancient Greeks, but 
the general acceptance of the idea of organic evolution is due to 
