192 THE TROPICAL WORLD. 



ing the resin consisted in felling the tree, which was then placed 

 in a slanting position, so as to enable the exuding fluid to be 

 collected in banana leaves. This barbarous proceeding, which 

 from the enormous demand which suddenly arose for the gutta 

 Avould soon have brought the rapidly rising trade to a suicidal 

 end, fortunately became known before it was too late, and the 

 resin is now gathered in the same manner as caoutchouc, by 

 making incisions in the bark with a chopping knife, collecting 

 the thin, white, milky fluid which exudes in large vessels, and 

 allowing it to evaporate in the sun or over a fire. The solid 

 residuum, which is the gutta percha of commerce, is finally 

 softened in hot water, and pressed into the form of slabs. 



Gutta percha has many properties in common with caout- 

 chouc, being completely insoluble in water, tenacious, but not 

 elastic, and an extremely bad conductor of caloric and electri- 

 city. The name of vegetable leather which has been applied to 

 it, gives a good idea both of its appearance and tenacity. 



Its uses are manifold. It serves for water-pipes, for vessels 

 fit for the reception of alkaline or acid liquids which w^ould cor- 

 rode metal or wood, for surgical implements, for boxes, baskets, 

 combs, and a variety of other articles. The wonder of the age, 

 submarine telegraphy, could hardly have been realised without 

 it, as it is only by being cased in so isolating a substance, and 

 one so impermeable by water, that the metallic wire is able to 

 transmit the galvanic stream through the depths of ocean from 

 land to land. 



Of all the dyeing substances which the tropical zone produces 

 in such endless variety, none is more important in a commercial 

 point of view than indigo. Various species of plants pro- 

 ducing this beautiful cerulean colour are found growing 

 spontaneously in the warmer countries of both hemispheres, 

 but the Indigofera tinctoria is most generally cultivated. The 

 knotty shrubby plant rises about two feet from the ground; 

 the leaves are winged like those of the acacia, smooth and soft 

 to the touch, furrowed above, and of a darker colour on the upper 

 than the under side. The small reddish flowers which grow in 

 ears from the axillae of the leaves have no smell, and are suc- 

 ceeded by long crooked brown pods, which contain small yellow 

 seeds. The plant requires a smooth rich soil, well tilled, and 

 neither too dry nor too moist. A child of the sun, it cannot be 



