r supply under our
own control and, if possible, within our own country. Rubber is not rare
in nature, for it is contained in almost every milky juice. Every
country boy knows that he can get a self-feeding mucilage brush by
cutting off a milkweed stalk. The only native source so far utilized is
the guayule, which grows wild on the deserts of the Mexican and the
American border. The plant was discovered in 1852 by Dr. J.M. Bigelow
near Escondido Creek, Texas. Professor Asa Gray described it and named
it Parthenium argentatum, or the silver Pallas. When chopped up and
macerated guayule gives a satisfactory quality of caoutchouc in
profitable amounts. In 1911 seven thousand tons of guayule were
imported from Mexico; in 1917 only seventeen hundred tons. Why this
falling off? Because the eager exploiters had killed the goose that laid
the golden egg, or in plain language, pulled up the plant by the roots.
Now guayule is being cultivated and is reaped instead of being uprooted.
Experiments at the Tucson laboratory have recently removed the
difficulty of getting the seed to germinate under cultivation. This
seems the most promising of the home-grown plants and, until artificial
rubber can be made profitable, gives us the only chance of being in part
independent of oversea supply.

There are various other gums found in nature that can for some purposes
be substituted for caoutchouc. Gutta percha, for instance, is pliable
and tough though not very elastic. It becomes plastic by heat so it can
be molded, but unlike rubber it cannot be hardened by heating with
sulfur. A lump of gutta percha was brought from Java in 1766 and placed
in a British museum, where it lay for nearly a hundred years before it
occurred to anybody to do anything with it except to look at it. But a
German electrician, Siemens, discovered in 1847 that gutta percha was
valuable for insulating telegraph lines and it found extensive
employment in submarine cables as well as for golf balls, and the like.

Balata, which is found in the forests of the Guianas, is between gutta
percha and rubber, not so good for insulation but useful for shoe soles
and machine belts. The bark of the tree is so thick that the latex does
not run off like caoutchouc when the bark is cut. So the bark has to be
cut off and squeezed in hand presses. Formerly this meant cutting down
the tree, but now alternate strips of the bark are cut off and squeezed
so the tree continues to live.

W