5o8 NOTES OF A BOTANIST chap, xiv 
short - leaved Seringa. The former yields most 
milk, but neither is so productive as that of Para 
{S. brasiliensis)} Both are straight, tall, and not 
very thick trees, with rather thin and smooth bark, 
and their average height may be about lOO feet. 
Near the Barra some milk is taken from a speci-es 
common on the river banks (kS. elastica ?), but there 
is another species growing in the interior of the 
forest said to yield more milk. This I have not seen. 
The species of Siphonia I have gathered on the 
Amazon and Rio Negro amount to seven or eight, 
and it is probable that two or three times as many 
yet remai-n to be discovered. On the Uaupes I 
met with two trees (2427, 2479, hb.) of a genus 
apparently not far removed from Siphonia, which 
yield pure rubber, and are also called by the Indians 
Xeringui ; but the single (not ternate) leaves and 
the clustered trunks (often as many as ten from a 
root) give these trees an aspect very different from 
the Siphonia.^ 
When I ascended the Rio Negro in 1851, I 
showed the inhabitants the abundance of rubber 
trees they possessed in their forests, and tried to 
induce them to set about its extraction, but they 
shook their heads and said it would never answer. 
At length the demand for rubber, especially from 
the United States, began to exceed the supply ; the 
price consequently rose rapidly, until early in 1854 
it reached the extraordinary price of 38 milreis 
(;^4 : 8 : 8) the arroba, a little over 5s. a pound. 
The extraction of caoutchouc from the various 
1 [The name Hevea is now usually adopted for the trees formerly known as 
Siphonia. — Ed.] 
^ [In Spruce's MSS. (Plantoe Amazonicae) he makes these a new genus 
Muranda, and the species M. siphonoides and M. minor. — Ed.] 
