li'i^J Hall-Goodsp<'((l: Chnjsil 251 



years old. Wood which is just in its second year may or may not be 

 worth preserving, depending upon methods of milling, local conditions, 

 and the value of the rubber. The age is easily determined in young 

 stems by counting the growth rings. The color and texture of the 

 bark may also be used as a guide by one familiar with the plant. The 

 removal of all growth of less than three years will take with it all of 

 the leaves, but these, like the twigs themselves, carry only traces of 

 rubber. 



XIII. POSSIBILITIES OF CHRYSOTHAMNUS AS A 

 CULTIVATED PLANT 



It is eminently desirable that a portion of the rubber consumed in 

 the United States should be produced within our own borders. It is 

 the only important commodity essential to modern warfare which we 

 have not yet learned to produce. If tlie industry of rubber growing 

 Avere once established, even though it yielded only a fraction of our 

 normal needs, we could, through economy in use and through govern- 

 mental encouragement in war time, render ourselves independent of 

 other nations, who might refuse to supply our needs or who might be 

 unable to transport their products across the seas. 



These same arguments can be advanced for the support of investi- 

 gations looking to the production of synthetic rubber and there is no 

 doubt that this line of work should also be encouraged. It is even pos- 

 sible that the synthetic product will in time replace that from the 

 plantations. We are not in a position to forecast what the future may 

 bring forth in this connection, but the opinion of those best capable of 

 judging seems to be that high grade synthetic rubber in large quan- 

 tities is something which we need not expect for a long time to come, 

 if at all. In the meantime, dependence must be placed upon importa- 

 tions unless we can discover some commercially profitable method of 

 growing rubber plants in our own country. The list of plants to be 

 considered in this connection is a long one. It includes various exotics 

 some of which are now grown in foreign countries for their rubber but 

 none of which have been given a conclusive trial here. Certain of our 

 native latex bearing plants, such as the milkweeds, spurges, dogbanes, 

 etc., are now under investigation by the Carnegie Institution of Wash- 

 ington with some promise of success.-^ The Pinguay, or Colorado 



21 Caruegie lust., Wash. Year-book no. 17 (1918), p. 297. 



