r; how could they grow on the bare
rock?

"Well, Daisy?" said her friend, watching how Daisy's countenance woke up
from its subdued expression.

"Dr. Sandford, how could these things grow on the rock? these green
things?"

"What green things?"

"Why, ever so many sorts. Here is moss, a great deal of it, of different
kinds; and there is beautiful brake at the top, like plumes of feathers.
How can they grow there?"

"Why not?"

"I thought everything wanted some earth to grow in."

"Have they none?"

"I don't know. I thought not. They must have very little indeed, Dr.
Sandford."

"Very little will do, I suppose."

"But I do not see how _any_ earth got there," said Daisy. "It was only a
bare rock at first, of course."

"At first," repeated the doctor. "Well, Daisy, I suppose it was no more.
But there is something else growing there, which you have not spoken
of."

"Is there?" said Daisy. "I do not see anything else."

"Pardon me--you do see it."

"Then I do not know what it is," said Daisy laughing. Absolutely, the
sober, sober little face had forgotten its care, and the eyes were
alight with intelligence and curiosity, and the lips were unbent in good
honest laughter. The doctor raised himself up to a sitting posture.

"What do you call those grey and brown patches of colour that hide your
rock all over?"

"Grey and brown?" said Daisy wistfully--"those are just the colours of
the rock, aren't they?"

"No. Look close."

"Why, Dr. Sandford, what is it? It is not the rock--some of it is
not--but here is a spot of yellow that is nothing else, I think."

"You must learn not to trust your eyes, Daisy. That is something that
grows; it is not rock; it is a vegetable. If I had my pocket lens here
I would shew you; but I am afraid--yes, I have left it at home."

"Why it is!" cried Daisy. "I can see now--it is _not_ rock. What is it,
Dr. Sandford?"

"Lichen."

"What is that, sir?"

"It is one of the lowest forms of vegetable life. It is the first dress
the rocks wear, Daisy."

"But what does it live on?"

"Air and water, I suppose."

"I never knew that was a vegetable," said Daisy musingly. "I thought it
was the colour of the rock."

"That goes to prepare soil for the mosses, Daisy."

"O how, Dr. Sandford?"

"In time the surface of the rock is crumbled a little by its action;
then its own decay furnishes a very little addition to that. In
favourable situations a stray oak leaf or two falls a