LUTHER BURBANK 
But with the modern tendency to apply scientific 
methods to forestration in general, doubtless the 
question will ultimately arise as to whether the 
turpentine trees may not be improved along with 
the timber producers. 
That trees of the same species differ quite 
radically in the amount of the valuable juices is 
certain, so there would appear to be no reason 
why it may not be possible to develop varieties of 
trees that will be conspicuous for this quality, just 
as other trees have been improved as to their 
powers of growth or their capacity to produce 
abundant crops of fruit. 
VARIED PRODUCTS OF THE PLANT LABORATORY 
An incidental use of the resinous exudate of 
the pine tree that has come to assume considerable 
economic importance is the production of chewing 
gum. 
The habit of gum chewing appears to have 
originated or at least to have gained chief popu- 
larity in America in comparatively recent times. 
The resin that exudes from the spruce was the 
substance that was chiefly used, under the name of 
spruce gum, until somewhat recently. But of late 
years the chewing gum industry has reached pro- 
portions that make it impossible to meet the 
demand from this source. And it has been found 
that ordinary resin, combined with sugar and lin- 
[258] 
