=Logwood= (Haematoxylon campeachianum).—­This is a moderate-sized tree with a very contorted trunk and branches, which are beset with sharp thorns, and blooms with a yellow flower.  It is a native of Central America and the West Indies.  This valuable dye-wood is imported in logs; the heart-wood is the most valuable, which is cut up into chips or ground to powder for the use of dyers by large powerful mills constructed especially for the purpose.  Logwood, when boiled in water, easily imparts its red colour.  If a few drops of acetic acid (vinegar) is added, a bright red is produced; and when a little alum is added for a mordant, it forms red ink.  If an alkali, such as soda or potash, is used instead of an acid, the colour changes to a dark blue or purple, and with a little management every shade of these colours can be obtained.  Logwood put into polish or varnish also imparts its red colour.

=Fustic= (Maclura tinctoria).—­This tree is a native of the West Indies, and imparts a yellow dye.  Great quantities are used for dyeing linens, etc.  The fustic is a large and handsome evergreen, and is imported in long sticks.

=Turmeric= (Curcuma longa).—­Turmeric is a stemless plant, with palmated tuberous roots and smooth lance-shaped leaves.  It is imported from the East Indies and China.  The root is the part which affords the yellow powder for dyeing.  It is also a condiment, and is largely used in Indian curry-powder.  Paper stained with turmeric is used by chemists as a test for alkalies, and it is also used in making Dutch, pink, and gold-coloured varnishes.

=Indigo= (Indigofera tinctoria).—­Indigo is a shrub which grows from two to three feet in height, and is cut down just as it begins to flower.  It is cultivated in almost all the countries situated in the tropics.  The dye substance is prepared from the stems and leaves, and is largely used in calico-printing.

=Persian Berries= (Rhamnus infectorius).—­These berries are the produce of a shrub of a species of buckthorn common in Persia, whence they derive their name; but large quantities are also imported into England from Turkey and the south of France.  The berries are gathered in an unripe state, and furnish a yellow dye.

=Nut-galls.=—­These are found upon the young twigs of the Turkish dwarf oak (Quercus infectoria), and are produced by the puncture of an insect called Cynips.  The supply is principally from Turkey and Aleppo.  Nut-galls contain a large quantity of tannin and gallic acid, and are extensively used in dyeing.

=Catechu.=—­This is obtained from the East Indies, and is the extract of the Acacia catechu, a thorny tree.  The wood is cut up into chips similar to logwood, and after boiling and evaporation the liquor assumes the consistency of tar; but when cold it hardens, and is formed into small squares.  It is extensively used by tanners in place of oak bark.