ON GUM AND SUGAR TREES 
refer in another connection, was gathered and its 
juices extracted for the making of the pigment 
madder. But it would not pay to undertake this 
work now, since the chemist has learned how to 
make madder from coal tar and hence has substi- 
tuted for a plant industry an enterprise associated 
with the manufacture of gas. 
It will doubtless be a long time before the 
manufacture of artificial rubber makes corre- 
sponding encroachments on the industry of manu- 
facturing rubber from the plant juices. Still it is 
quite within the possibilities that this may come 
to pass in the course of the coming generation. 
In the meantime, the rubber industry is a vastly 
important one, and the principal trees that supply 
the juices that on evaporating constitute rubber 
are cultivated in vast plantations in various trop- 
ical regions. Moreover rubber is gathered from 
wild trees of several species, although in recent 
years the cultivated trees have largely been de- 
pended upon to meet the growing needs of the 
industry. 
Trees of the genus Hevea are the most import- 
ant source of rubber. But there are many other 
trees, the juices of which contain the essential con- 
stituents of rubber in the right combination, and a 
good many of these have commercial possibilities. 
I have referred in another connection to my 
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