The President's Address. 109
other groups would thus be encouraged to follow it up by
catalogues of their own special objects of study. There is
yet another point to be mentioned in connection with the
preparation of such lists, and that is the possible occurrence
of local variation. Of course we cannot expect in such a
limited area to find many or well-marked instances of this
phenomenon, but it nevertheless seems to me desirable to
make a most careful comparison, especially in the case of
variable species, between series from the various portions
of our own county and series from other parts of the
country and from the Continent. This is the more espe-
cially desirable with common and variable species which
extend to our marsh-fringed coast. Mr. H. W. Bates tells
us that in the Amazon Valley the butterflies undergo modi-
fication to such an extent that many species appear to
change into a distinct local race in every fresh district. It
is obviously useless to look for such striking instances in a
small island like ours, where there are but few facilities for
isolation, and where local variation is consequently oblite-
rated by free intercrossing. But there is no reason why
the phenomena which occur in the tropics en grand should
not appear in this country en petit, and a searching exami-
nation of long series of specimens in the manner suggested
may possibly result in the discovery of some positive
evidence in this direction.
The next suggestion is one that appeals to our botanists.
We have had recently added to our Forest large tracts of land
formerly under cultivation, but now being gradually recon-
verted into forest land. It appears to me that we have
here a natural experiment going on of which we should
take advantage: we can surely learn something of the
manner in which a forest spreads by keeping a careful
. watch upon such tracts, noting the plants that from time
to time make their appearance, and by this means recording
the encroachment of species, and observing the effects of
that struggle for life which is one of the prime factors in
the evolution of living forms.
One other suggestion, and I have finished. Now that
our sylvan head-quarters have so much increased in extent