THE ECONOMIC BIOLOGY OF PLANTS 461 



Rubber is made from the milky juice of several tropical trees 

 of South America and Asia; its uses are many and varied and 

 familiar to most of us. 



Tanning Materials. The principal tanning- materials are ob- 

 tained from the bark of the oak, hemlock, willow, birch (Russia 

 leather), chestnut, and the South American quebracho. 



Dye stuffs. Vegetable dyes have become much less important 

 since the development of the coal tar or aniline colors, however 

 indigo, logwood, and gamboge may be mentioned. The indigo 

 plant grows in India and Java and furnishes the familiar blue 

 dye; logwood grows in Central and South America and fur- 

 nishes red and black dyes, while gamboge is a yellow dye grown 

 in Siam. 



Drugs. Several drug products have been mentioned elsewhere 

 so that merely a brief list will be given here : 



Gums: Camphor (China), Arabic (Africa), Tragacanth (Asia). 



Witch hazel from leaves and stems of a native plant. 



Opium from milk of Chinese and Indian poppy fruits. 



Cocaine from coca leaves (Peru). 



Quinine from chinchona bark (Peru). 



Strychnine, atropine, and nicotine are important plant drugs. 



Alcohol is one of the most important plant drug products; it 

 has a multitude of uses other than as a beverage. It is utilized in 

 all chemical industries, as a solvent, fuel, preservative, and in 

 many other useful ways. 



Alcohol is made by the action of yeast ferments on several kinds 

 of sugars. Apples, rye, and corn furnish whiskey; barley malt 

 is used for beer; grapes provide the sugar solution for wines; 

 molasses ferments to make rum. 



All of these and some waste sugar liquors are fermented and 

 distilled to make commercial alcohol. 



Distillation Products. The last topic in our list of plant uses 

 includes several products from distillation of wood or pitch. Crude 

 turpentine is the pitch of certain kinds of pine found in our South- 

 ern States, France, and Russia. From it the common turpentine 

 is made by distillation and rosin is left as a residue. Turpentine 



