Rubber is coagulated sap; the French word for it, caoutchouc, comes from a South American Indian word meaning “the wood that weeps.” The wood that wept in the Congo was a long spongy vine of the Landolphia genus. Up to a foot thick at the base, a vine would twine upward around a tree to a hundred feet or more off the ground, where it could reach sunlight. There, branching, it might wind its way hundreds of feet through the upper limbs of another half-dozen trees. To gather the rubber, you had to slash the vine with a knife and hang a bucket or earthenware pot to collect the slow drip of thick,
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