388 PLANTS AND MAN 



materials used annually in this country. Of the native tannin 

 producing species, chestnut is the most important present source, 

 its wood supplying about 60% of the domestic tannins. It is 

 followed by chestnut oak bark and eastern hemlock bark, each of 

 which contribute to the extent of 18%. In California, the tan- 

 bark oak supplies most of the material for tannin extraction. 

 Western hemlock bark contains a higher percentage of tannin 

 than that of the eastern hemlock, but the bark is thin, and the 

 best stands are located in rather inaccessible areas, so that it is of 

 no great present day importance, but may serve as a future supply 

 of domestic tannins. Since tannins are soluble in water, they are 

 extracted from chipped or ground wood or bark by hot water. 

 Following extraction the extract is distilled, strained, and con- 

 centrated to the desired strength by evaporation. 



The world's most important single source of tannin is the 

 Quebracho, a hard, heavy, tropical wood from South America. 

 About a million tons are cut annually for tanning extracts, and 

 the yearly growth of the forests offsets the annual cut. The heart- 

 wood of this species is a more concentrated source of tannin than 

 any other wood, yielding up to 28 % of its weight in tannins. 



Mangrove bark, from another tropical tree, has reached some 

 commercial importance in the United States. Most of the present 

 day supply comes from South America. Other foreign sources of 

 tanning materials include myrobalan nuts which are the fruit 

 of several tree species cultivated in India; divi-divi which is the 

 seed pod of a small tree native to Central and South America; 

 imported sumach from the Mediterranean region; and Valonia, 

 the acorn from the Turkish oak of Asia Minor. 



Until shortly after the Civil War most of our dyestuffs were of 

 vegetable origin, but since then, and particularly in the last ten 

 to twenty years, the use of synthetic dyes has increased greatly, 

 with a corresponding decrease in the use of plant materials as 

 sources of coloring matter. However, for certain uses, dyewoods 

 are still in demand. Most of these are tropical woods, imported 

 from Central and South America and the West Indies. Logwood 

 makes up about three-fourths of all the dyewoods imported, 



