n can be crossed with the
oak; that all the walnuts freely hybridize with each other and with the
open bud hickories, a class which includes the toothsome and profitable
pecan. There is in California a tree which is considered to be a cross
between the native walnut and the live oak. The Mendelian Law in
connection with past achievements in plant breeding, and the experiments
of Loeb in crossing the sea urchin and the star fish are profoundly
suggestive.

The possibilities of plant breeding as applied to crop yielding trees
seem to be enormous. They certainly warrant immediate and widespread
effort toward the creation of useful strains which may become the basis
of a new agriculture yielding food for both man and the domestic
animals.

(B) The time for constructive conservation has come. Our most vital
resource is the soil. It is possibly the only resource for which there
is no substitute. Its destruction is the most irreparable waste. So long
as the earth remains in place the burnt forest may return and the
exhausted field may be restored by scientific agriculture. But once the
gully removes this soil, it is the end so far as our civilization is
concerned--forest, field and food are impossible and even water power is
greatly impaired. Our present system of agriculture, depending upon the
grains, demands the plowing of hillsides and the hillsides wash away.
This present dependence upon the plow means that one-third of our soil
resources is used only for forest, one-third is being injured by
hillside erosion, and only one-third, the levelest, is being properly
used for plow crops.

The present alternative of Forestry for hillsides is often impossible
because the yields are too meagre. Almost any land that can produce a
forest, and much that has been considered too dry for forest, can
produce an annual harvest of value to man or his animals when we have
devoted sufficient attention to the breeding of walnuts, chestnuts,
pecans, shellbarks, acorn yielding oaks, beech nuts, pine nuts, hazel
nuts, almonds, honey locust, mesquite, screw bean, carob, mulberry,
persimmon, pawpaw, and many other fruit and nut trees of this and other
lands.

The slowness and expense of the process of plant introduction and tree
breeding limits this work to a few individuals with patience and
scientific tastes and to governmental and other institutions of a
permanent nature. The United States Government and each state experiment
station shou