Here and there were groves of mulberries,--the tree
on which the silk worm feeds,--and there were vineyards, with the vines
just bursting into leaf, and now and then a little garden of orange
trees. In the mean time the postilions kept cracking their whips, and
the horses galloped on at such a speed that Rollo had scarcely time to
see the objects by the road side, they glided so swiftly by.

"Won't the silk worms eat any kind of leaves but mulberry leaves?" he
asked.

"No," said Mr. George, "at least the mulberry silk worms will not. There
are a great many different kinds of silk worms in the world; that is,
there are a great many different kinds of caterpillars that spin a
thread and make a ball to wrap up their eggs in, and each one lives on a
different plant or tree. If you watch the caterpillars in a garden, you
will see that each kind lives on some particular leaf, and will not
touch any other."

"Yes," said Rollo, "we found a big caterpillar once on the caraway in
our garden, and we shut him up in a box, in order to see what sort of a
butterfly he would turn into, and we gave him different kinds of leaves
to eat, but he would not eat any but caraway leaves."

"And what became of him at last?" asked Mr. George.

"O, he turned into a butterfly," said Rollo. "First he turned into a
chrysalis, and then he turned into a butterfly."

"There are a great many different kinds of silk worms," said Mr. George;
"but in order to find one that can be made useful, there are several
conditions to be fulfilled."

"What do you mean by conditions to be fulfilled?" asked Rollo.

"Why, I mean that there are several things necessary, in order that the
silk worm should be a good one to make silk from. In the first place,
the fibre of the silk that he spins must be fine, and also strong. In
the next place, it must easily unwind from the cocoon. Then the animal
must be a tolerably hardy one, so as to be easily raised in great
numbers. Then the plant or tree that it feeds upon must be a thrifty and
hardy one, and easily cultivated. The mulberry silk worm has been found
to answer to these conditions better than any hitherto known; but there
are some others that I believe they are now trying, in order to see if
they will not be better still. They are looking about in all parts of
the world to see what they can find."

"Who are looking?" asked Rollo.

"The Society of Acclimatation," replied Mr. George. "That is a society
founded