ON THE COMMERCIAL KINDS OF INDIJA-RUBBER. T 
that, caoutchouc is obtained at Para from Siphonia Brasiliensis, Willd. 
(and probably from several other species) ; on the Amazon, about the 
mouth of the Tapajoz, from S. Spruceana, Benth. ; towards the mouth 
of the Madeira are other species not seen by him in good state ; on 
the Rio Negro, Haupés, and Casiquiare, from S. discolor, Spruce, 
S. rigidifolia, Spruce, S. lutea, Spruce, S. paucifolia, Spruce, S. api- 
culata, Spruce, and from two other species. The india-rubber is 
collected by Indians, who generally unite together in large numbers 
for this purpose. In the province of Para it was computed that 
25,000 persons were engaged in its collection in 1854. The greatest 
difficulty is in cutting a pathway through the forest. By some the trees 
are either cut down or bound with boughs at top and bottom, and the 
milk drawn off at one operation,—thus destroying the trees; but by far 
the commonest method is that of tapping. After a tree has been once 
tapped, it requires rest for about two years to recover its strength. 
When the trees are flowering, nearly al! the milk goes to nourish the 
flowers, and scarcely any from the trunk is then to be obtained ; but if 
a panicle be cut, the milk starts out in large drops. A small quantity 
of alum is put along with the milk, as it assists the coagulation of the 
caoutchouc, whereas ammonia has the contrary effect. After the milk 
is collected, the Indians gather heaps of Urucuri nuts (the fruit of 
Altalea excelsa, Mart.), which give off a thick white smoke. They 
then dip their clay moulds in the milk, and holding them over the fire, 
repeat the dippings till a sufficient thickness has been obtained,—thus 
giving rise to the laminated appearance observable in Para bottle rubber. 
By some this smoking process has been questioned ; but Dr. Spruce, 
in his letter, says, ** India-rubber was certainly smoked when I was 
on the Amazon. The smoke used was produced by heating (toasting 
or roasting, not properly burning) the hard but somewhat oily nuts of 
the Urucuri-Palm (Attalea excelsa, Mart.). It was very white and va- 
porous, and deposited no fuliginous matter whatever. A recently- 
made smoke-dried india-rubber shoe was of a straw-colour, or pale 
yellow brown; so that Martius was wrong in supposing * Incolæ fruc- 
tus tostos ad fumigandum succum Siphonie elastic adhibent, ut re- 
sine elasticee nigrum colorem comparent. " The mistake, I believe, 
has arisen from the change of colour from the yellowish-white to 
brownish-black tinge, which Para rubber assumes on exposure to 
the atmosphere, being attributed to the action of the smoke; whereas, 
