Ckapter 23 



INDUSTRIAL USES OF PLANTS 



Strictly speaking, many plants used by man are the basis of 

 industries — the textile industry dependent upon the fiber plants 

 discussed in Chapter 20, the rubber industry supported by the 

 latex producing plants discussed in Chapter 21, etc. There are a 

 number of other industrial uses of plants, however, which are not 

 of sufficient importance to justify more than a few pages of 

 treatment in a general work of this sort, and which accordingly 

 are grouped for discussion in this chapter. It seems quite proba- 

 ble that some of these plant uses are on the wane, and that others 

 are destined for places of far greater importance than they occupy 

 at the present time. 



Resins and Gums 



Resins are extremely complex chemical substances which 

 occur as secretions in plants, generally in definite passages or 

 cavities. They have their origin in essential oils, being oxidation 

 products of these substances. Upon continued exposure to air, 

 resins harden due to the further evaporation and oxidation. 

 From the plant's standpoint, resins are probably useful in pre- 

 venting decay and entrance of diseases and insects, since there 

 generally is a copious resin flow when the plant is wounded. 

 From man's standpoint, resins are important because they can be 

 collected from their plant or fossil sources, dissolved in some 

 volatile solvent such as alcohol, and spread on surfaces in the 

 form of a varnish which gradually hardens to leave a thin, water- 

 proof coat as the solvents and essential oils evaporate. This use of 

 resins is no modern invention, since the ancient Chinese, Japa- 

 nese, Egyptians, Greeks, and Romans were all familiar with 

 varnishes and lacquers. 



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