al of
the fittest. They have won, so when we are dealing with native plants
against our native diseases, we have a condition that has been fought
out in nature for nobody knows how many thousand years. The result is
that unless we disturb the balance too much by cultivating great
orchards of a thing that has been grown as scattered individuals, or
overforcing it or selecting and breeding towards larger fruit without
any regard to foliage and other characters we can go ahead with our
breeding and selection and cultivation and trust nature to keep the
balance to some extent. We have this natural balance in our favor in
dealing with the problem of cultivating native plants. As an example
take the pear and apple blight. The pear blight problem is one in which
a native parasite on wild crab apples, which occasionally kills a few
twigs here and there, attacks the juicy, tender, susceptible, introduced
European pear and makes a very serious disease. It is a fight indeed to
grow it in so much of the country that pear culture has been very
largely suppressed over the eastern half of the United States and part
of the Pacific coast. All this trouble has been caused by one little
native microbe. Apple culture also, with certain varieties, has been
seriously interfered with in some sections.

The apple cedar rust is probably the most striking example of a native
parasite attacking a foreign host that we know of, and particularly so
as the remarkable evolution in which the parasite has adjusted itself to
the new host is taking place right now every year. The apple cedar rust
is becoming a more difficult problem clear across the eastern United
States to Nebraska. It has occurred as a serious disease since 1905 to
1907. As a botanical curiosity we have known it a long time, but as a
serious disease, it is very recent, and nobody knows yet how serious it
is going to be.

We have a very striking example of this introduction of a foreign plant
and the plant being attacked by a native parasite, in the case of the
filbert blight, and I am going to take that up later. The trouble is
that we have brought into the United States a European filbert and it
has been attacked by a parasite of our wild hazelnuts. The disease is
very rare and is seldom seen on the wild hazelnut,--so rare that it was
hardly known by scientific botanists, and yet it interferes with filbert
culture in the eastern United States and is the one thing more than
anything e