SOME USEFUL PLANTS 339 
latter. These “nitrogen-fixing bacteria” therefore afford 
an unlimited supply of nitrogen available for the nutrition 
of the higher plants almost without expense to the farmer 
and gardener. 
(5) TANNING MATERIALS, DYES, VARNISHES, AND 
MISCELLANEOUS PRODUCTS OF 
VEGETABLE ORIGIN 
414. Many of the substances mentioned under this head 
are fully discussed in treatises on the chemistry of various 
manufacturing industries. All that can be done in this 
place is to give a few examples of plant products used in 
manufacturing processes. 
Vegetable dyes are no longer nearly as important as 
they were before the discovery of aniline colors. Antique 
Oriental rugs and other articles, however, show well how 
much superior are the soft shades produced by dyes of 
vegetable origin. A large number of dyestuffs are ob- 
tained from tropical or sub-tropical plants of the Pea 
family ; among these are Brazil wood, logwood, camwood, 
and indigo. 
Varnishes usually consist of some kind of rosin dis- 
solved in alcohol, oil of turpentine, or linseed oil. Among 
the most valuable varnishes are shellac (from trees of the 
Mulberry family), copal (Pea family), and Japanese lacquer 
(Sumach family). 
Common rosin and turpentine are made from the sap of 
pine trees, particularly our longleaf southern pine. Deep 
cuts are made through the bark into the wood, and from 
these a pitchy liquid slowly flows. By distilling, this 
is separated into a nearly colorless liquid, oil of turpentine, 
commonly called “spirits” of turpentine, and the familiar 
