LITTLE-KNOWN PLANTS 



163 



principally to the Chinese. Some plants are used for 

 dyeing purposes. In early times, the indigo plant 

 was an important crop in Virginia. 



Sources of Tannin. Many plants are raised for 

 the tannin in them. Tannin is a material used for 

 tanning skins. It is 

 obtained from the bark 

 of some trees, like the 

 oak and hemlock. 

 Canaigre is a plant 

 belonging to the dock 

 family, which is grown 

 for the tannin con- 

 tained in the thick 

 roots. 



Rubber. Most of 

 our rubber comes from 

 the rubber trees of 

 Mexico, Central Amer- 

 ica, and South America. 

 The milky sap of these 

 trees is used to make 



, , rrr, . VANILLA BEAN 



rubber. The sap is 



obtained by making shallow cuts in the bark of the 

 rubber trees and collecting the sticky liquid as it flows 

 from the cuts. A shrub, called guayule, that grows 

 in southwestern United States and northern Mexico, 

 contains a sap from which rubber can be made. 

 Many other plants have sap that may be successfully 



