TREE PRODUCTS 185 



ered from wild trees of several species, although 

 in recent years the cultivated trees have largely 

 been depended upon to meet the growing needs 

 of the industry. 



Trees of the genus Hevea are the most im- 

 portant source of rubber. But there are many 

 other trees, the juices of which contain the essen- 

 tial constituents of rubber in the right com- 

 bination, and many of these have commercial 

 possibilities. 



I have referred in another connection to my 

 experiments with tropical plants of the genus 

 Asclepias, relatives of the familiar milkweed. 



Tentative experiments have been undertaken 

 to discover whether these plants might be devel- 

 oped to a stage that would make them commer- 

 cially valuable as producers of rubber. The re- 

 cent discoveries of the chemist make experiments 

 in this line somewhat less valuable than they 

 hitherto seemed. Yet the demand for rubber is 

 so great, in these days of electricity and auto- 

 mobiles, that there seems just now little danger 

 of overstocking the market. And if a plant 

 could be developed that could be grown in tem- 

 perate regions, and that would produce the rub- 

 ber-forming juices in adequate quantity, such a 

 plant would constitute a very valuable acquisi- 

 tion for a long time to come, even should natural 



