LUTHER BURBANK 
seed oil, with some flavoring added, serves the 
purpose of the original spruce gum so the latter is 
now seldom seen in the market. More recently 
chicle, a gummy substance which exudes from 
several tropical trees, has been imported in great 
quantities, and is now supplanting all other sources 
of gum. 
The supplying of turpentine and its products 
gives the conifers high range among trees that 
produce commercial by-products of great import- 
ance. But with the exception of the pines, the 
trees that produce really important exudates or 
oils or chemicals are indigenous to the tropics, or 
at least are confined to the warm temperate zone. 
I have thought many times in recent years that I 
should like to have a plant laboratory in the 
tropics for the testing of tropical plants as to the 
production of useful commercial products, and for 
the development of improved varieties of plants 
the products of which are already utilized. 
It would be worth while, for example, to make 
very extensive experiments by way of testing the 
qualities of the different trees that deposit in their 
bark the bitter compound known as alkaloids, a 
galaxy of which are prized for their medicinal 
properties. These are very complex combinations 
of carbon, hydrogen, oxygen and nitrogen. That 
is to say, they have the same constituents as proto- 
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