"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 and lies there, and
also decays, and by and by there is a little coating of soil or a little
lodgment of it in a crevice or cavity, enough for the flying spores of