Silk-Rubber. 
This is derived from the milky sap of an Apocynaceous tree 
Kickxia elastica Preuss, native of the tropical regions of west 
Africa from Kameroon to the Gold Coast. It is considered one 
of the very best of the recently discovered rubber-producing 
species. In its home it grows from a few hundred to 3,000 feet 
above sea level and is said to require about the same climatic 
conditions as cacao. The milky sap of this tall forest tree is 
extraordinarily rich in rubber of a superior quality, as high as 
58% having been found. A seven-year-old tree is reported by 
R. Schechter as having yielded 70.5 ounces of rubber which 
dried to about 60 ounces. 
The sap is collected, mixed with 3 to 6 times its volume of 
water and is then boiled. The rubber rises to the surface, is 
skimmed off, washed in cold water and then pressed into sau- 
sage-shaped masses. Various salts and acids are also used for 
coagulating the sap without heating it. The tree is a large one, 
often reaching 100 feet or more in height, and in favorable 
situations growing with extraordinary rapidity. It does not 
seem to be especially particular in regard to its soil require- 
ments, but undoubtedly requires high temperatures and a high 
degree of humidity. 
ASIATIC RUBBER PLANTS. 
The Asiatic rubbers are derived from both trees and vines. 
Assam rubber. This comes from the well-known "Rubber 
Plant" of the horticulturist, Ficus elastica Eoxb. This enor- 
mous forest tree is a native of the valleys and lower slopes of 
the whole southern Himalayas, also extending through the 
countries of southern Asia to Java and the Malayan archipelago. 
It often grows to a height of 150 to 180 feet, with a clump of 
trunk-like aerial roots many yards in diameter. The seeds of this 
tree usually germinate in the top of some nearby tree of a dif- 
ferent species, and throw out long aerial roots which at first 
hang pendant but on reaching the ground themselves throw out 
feeding roots and increase in diameter until they reach trunk- 
like proportions. One of these air-roots if destroyed at the 
base will die below the point of injury but will throw out new 
aerial roots above, these in turn lengthening until they reach 
the ground and again throw out feeding roots. In 
this regard Ficus elastica is similar to the Ohia Lehua of the 
windward forests of Hawaii with its much-branched and many 
bodied trunks which in the beginning were really the aerial 
roots of the epiphytic ohia seedling. 
