290 INDUSTRIAL PLANTS 



uncertain, but it is now known that the finest copal of 

 the East is a product of the Zanzibar copal-tree while 

 the best South American copal is from the nearly related 

 courbaril-tree (Fig. 273). The difficulty of tracing the prod- 

 uct to its source arose from the fact that the best copal is 

 dug by the natives out of the earth often in tracts of country 

 from which all plants that could have produced it have dis- 

 appeared. The hard resin, sometimes covered by an ac- 

 cumulation of three or four feet of soil, is all that remains to 

 show the former existence of copal-trees at that place. It 

 is a fossil. The happy accident of finding leaves, flower-buds, 

 and flowers embedded in masses of Zanzibar copal, finally 

 gave the last link in a chain of evidence connecting the resin 

 with the species which produced it. The South American 

 copal is found embedded in the earth at the base of courbaril- 

 trees, and often contains bits of courbaril-bark. When the 

 resin exudes from the tree and solidifies it is still too soft 

 to be of commercial value; only the slow process of time, 

 perhaps centuries, can bring it to that state of almost glassy 

 hardness which renders it indispensable for making the most 

 durable varnish. 



78. Coloring matters of some sort are almost universally 

 present throughout the vegetable kingdom. In many cases 

 they can scarcely be supposed to be of any benefit to the 

 plant which produces them but must be regarded as merely 

 waste products of the plant's activitj^ This is very com- 

 monly true of the vegetable coloring matters used in the in- 

 dustrial and the fine arts as dyestuffs, pigments, inks, or the 

 like. Such substances have been used from the remotest an- 

 tiquity. In recent times, however, vegetable dyestuffs have 

 come to be very largely replaced by various artificial com- 

 pounds such as the well-known aniline dyes prepared by 

 chemists from coal-tar. From among the vegetable pig- 

 ments and dyestuffs that are still of importance in the arts 

 gamboge, indigo, logwood, lampblack, and tan-l)ark ma}- be 

 selected as typical and famihar examples. 



Gamboge is a gum-resin obtained from the Siamese gamboge- 

 tree (Fig. 274) and other Asiatic species of the same genus. 

 The resinous material flows from the bark through cuts, 



