tivated rubber plantations begin to yield to the full extent of 
their capacity. 
Xo extensive new rubber forests are likely to be discovered, 
although investigators are almost daily adding names to the 
list of plants from which rubber may be secured. New rubbers 
require much experimentation before their relative commercial 
? % value becomes established. 
Artificial rubbers may resemble the natural article in some 
«V. tT#? ne °^ ^ s characteristics but none have thus far been produced 
' % \ which have the requisite elasticity. 
As to the third solution, while there can be no doubt that 
cultivated rubber plantations may ultimately supplant the prod- 
uct of the wild trees, it will undoubtedly be a matter of decades 
rather than years before even a parity between supply and de- 
mand is reached. In the meantime the question arises, if we 
are to plant rubber, to what particular variety shall we pin 
our faith. A consideration of the climatic conditions under 
which the various natural rubber producing plants thrive will 
therefore first be necessary. 
AMERICAN SPECIES OF RUBBER PLAXTS. 
Para Rubber. 
In 1904 nearly fifty per cent, of the world's supply of rubber 
came from the Amazon valley and the major share was classed 
as "Para." Para rubber is, has been and probably will contnue 
to be the standard of excellence with which all other rubbers 
are compared. It is in the main derived from a large tree, 
Hevea braziliensis, Muell. Arg., which grows wild in the trop- 
ical forest on the south bank of the Amazon and its tributaries, 
the Rio Purus, Rio Jurua, Rio Negro, Rio Madeira, and Rio 
Javary-Iquitos. So far as known, Hevea braziliensis only rare- 
ly occurs on the north side of the Amazon, but its place is there 
taken by other species of Heveas which yield rubber of inferior 
quality and secondary value. Hevea braziliensis is a stately 
tree often reaching the height of 130 feet with a trunk 3 to 1 
feet in diameter, the crown not very large but somewhat dense. 
The leaf is compound with three oval, sharp-pointed leaflets, 
dark-green above, bright-green on the under surface and rather 
prominently nerved. The flowers are small, yellowish-green, 
and the fruit a 3-celled capsule with 3 seeds as large as hazel- 
nuts. 
The trees are sparsely scattered through the tropical jungle 
over a region as large as Europe, and it is said that the native 
