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It cannot be wondered at then that these products can be easily 
overstocked. 
Rubber is however in a different position. It is exclusively a 
tropical product, no rubber plant of a^iy value having been met with 
outside the tropic area as above defined or having been successfully 
grown outside. 
There are four kinds of rubber trees which are practically the 
only ones of value for cultivation purposes, for though there are a 
number of other plants which produce a rubber of more or less 
value, the difficulty of growing them in the case of the rubber vines, 
for practical purposes, and the slowness of growth, and inferiority 
of product in the others exclude them from consideration. These 
four kinds are Para rubber, Rambong, Castilloa and Ceara rubber, of 
these the first two require a continuous rainfall, and can best be 
grown in the low country, Castilloa is^more suited for hill regions, 
and Ceara, is a desert plant preferring sandy regions. 
Para rubber seems to dislike a long spell of dry season, and if in 
such places it grows its growth is slow. It is also an inhabitant of 
alluvial plains requiring a fairly good soil. 
Taking the same area as before we may exclude as a possible 
producing area all Australia except possibly a small part of the 
extreme north, Cochin-China, and India, except perhaps parts of 
Burmah the whole of Africa (except perhaps a small part of the 
West coast), a region too dry and open for Para rubber and probably 
Rambong also; and a very large area of South America, 
The Eastern region of Brazil, Rio Grande del Norte, Pernambuco, 
and Bahia are dry campos covered with an open forest, and from 
what I have seen of them quite unsuited for the better class 
rubbers. The only wild rubbers in this region are the Mangabeira 
and Ceara, and it is highly improbable that either of these will 
interfere with rubber cultivation at all. In the more western parts 
of Brazil, Bolivia, Peru, the Amazonas district of Brazil, and as far 
north as Mexico the rubbers Hevea, Castilloa and probably Ram- 
bong could be and are being well grown. Some of the Polynesian 
islands may prove sources of rubber supply in the future, but in 
only the larger islands will it be possible to grow the plant success- 
fully, owing to the maritime nature of the greater part of the 
islands and it is on the whole not probable that the entire Polyne- 
sian area will ever produce any important supply of rubber. 
Meanwhile rubber is a product of universal use, a necessity of 
modem civilization, becoming more and more important every day, 
and being used directly or indirectly by everyone every day. 
Hitherto it has been only a jungle product, very little having been 
produced under cultivation. The area in which it has been pro- 
duced is almost exhausted of the product, and a large part of that 
area, (the greater part of Africa) is utterly unsuited for the cultiva- 
tion of any rubber plant of any value. The Landolphias of Africa 
tim 
