ssels to evaporate, and the solid substance left at the
bottom is the gutta-percha. It is not elastic, like India-rubber, and
is called 'vegetable leather' because of its toughness and leathery
appearance. It was discovered by an English traveler a long time before
it was supposed to have any useful properties, but now it is considered
a very valuable material. The wonderful submarine telegraph could not
convey its messages between the Old World and the New were not its wires
protected from injury by a coating of gutta-percha. Its unyielding
nature and its not being elastic render it the very material needed. The
long straps used in working machines are also made of gutta-percha, and
this is another instance where its non-elasticity gives it the
preference over India-rubber."

"And what is vulcanite?" asked Clara.

"It is caoutchouc mixed with sulphur. Unless a small quantity of
brimstone is added in the manufacture of overshoes, they become soft
when exposed to heat and hardened when exposed to cold; but it was
discovered that the sulphur will keep them from being affected by
changes in temperature. When a large amount of sulphur is used, the
India-rubber, becomes as hard as horn or wood, and this is the substance
called vulcanite. Now the gum is imported in masses, to be wrought over
by our skillful mechanics."

The children were very much pleased to find that they had learned the
nature of three important articles--India-rubber, gutta-percha and
vulcanite--and they thought it would be quite easy to remember the
differences between them.

"And now," said Miss Harson, "the last of these useful trees--the cow
tree, or milk tree--is the most curious one of all. Like the caoutchouc,
it is a native of South America; but the sap is a rich fluid that
answers for food, like milk. It is a fine-looking tree with oblong,
pointed leaves about ten inches in length and a fleshy fruit containing
one or two nuts. The sap is the most valuable part; and when incisions
are made in the trunk of the tree, there is an abundant flow of thick
milk-like sap, which is described as having an agreeable and balmv
smell. The German traveler Humboldt drank it from the shell of a
calabash, and the natives dip their bread of maize or cassava in it.
This milk is said to be very fattening; and when exposed to the air, it
thickens into a substance which the people call cheese."

"Milk and cheese from a tree!" exclaimed Malcolm. "Do you think we'd