FOREST TREES AND PRODUCTS OF THE TROPICS 219 
feet seven and a half inches in diameter, three feet 
from the ground, in seventeen years. 
Another great rubber-tree is a native of Central 
America and Mexico. It yields the Panama rubber 
of commerce... It is known to botanists as Castilloa 
elastica. The family name of this tree is a modifica- 
tion of the word Castile, a province in central Spain. 
This species is being extensively cultivated by Amer- 
icans in southern Mexico, especially on the Isthmus 
of Tehuantepec. 
A valuable substance similar to caoutchouc, called 
“balata,” is produced in the northern part of South 
America. It is the juice of the inner bark of a large 
tree, called by botanists Mimusops balata. The 
Dutch of Dutch Guiana call it “ paardenfleisch,” or 
“ horseflesh,” because of the color of its wood. The 
milk is drunk by the natives, and when diluted with 
water is used as cow’s milk. Balata is mixed with 
true rubber for various purposes. It is also used in 
the manufacture of beltings, and it is said that it may 
replace gutta-percha, which is now scarce, for pur- 
poses of insulation. 
Very few species of plants yield good rubber. 
Many plants are called rubber producers, but the 
product is usually of low grade in consequence of the 
presence of resin. The Brazilian rubber, which is the 
best, grows in regions unfit for human habitation. 
