124 PROF. BOWER: HOOKER LECTURE, I917. 
elements ” put forward, as accounting for progressive evolution, by Bateson 
in his Presidential address to the British Association in Australia. To me 
the process of Mendelian Segregation appears to be nothing more than a 
distributing agency. It constructs nothing: nor does it originate new 
morphological characters. We have to look elsewhere than to Mendelian 
Segregation for the origin of those structural innovations upon which 
progressive Evolution depends. The chief interest of Evolution lies in 
this initiation of new structural characters, rather than in the distributing 
agency to which they are subject. The obvious relation of their cumulative 
result to the environment, which we recognize as adaptation, carries with it 
homoplasy, or even convergent development in lines phyletically distinct. 
This is seen in high degree in the Filicales. It suggests, as the most 
probable interpretation of the facts, that some causal connection exists 
between the environment and those innovations which are the mark of 
structural progress. 
It has been impossible in this Lecture to do more than to give a slight 
sketch of the methods recently employed in elucidating the phylesis of the 
Filicales. Any more explicit statement of the results arrived at must be 
reserved for some other occasion. Meanwhile such results have been! used 
as an illustration of the modern method of Natural Classification. I hope 
what has been said may suffice to show that real progress is being made. 
Such measure of success in natural grouping as has been achieved among 
the Filicales may serve to stimulate like efforts directed to other groups of 
Plants. But it is useless to expect success to be as ready to hand in 
them as in the Filicales. These plants present an exceptionally favourable 
opportunity, owing to the nature of the evidence available. The Angio- 
sperms offer a still wider field ; but it suffers from deficiencies of evidence, 
which have already been explained. Moreover, the variety and extent 
of their special adaptations complicate the problem, and often tend to 
disguise the natural affinities. Still, it is not a hopeless quest to do the 
same for them. But what is urgently needed for success amid the multi- 
plicity of their lines of progress is a widening of the bases of comparison. 
There must be a recognition of new criteria. A revision of the relative 
values of the old criteria will also be necessary. These innovations, together 
with the more free discovery of fossils with structure from the Mesozoic 
Rocks, would provide the lines along which opinion may be expected to 
develop. It is with this hope that I have used the Filicales as an object- 
lesson in this Address. For the method which is being successfully applied 
to them may be confidently expected, sooner or later, to unravel even the 
tangled skein of Angiospermie Descent. Eventually it may lead to some 
more satisfactory, and assured arrangement of them according to Descent 
than has yet been achieved. 
