gh at the time he
was deposited in the "hole." When the bottom of the ravine was reached
he turned to the right, working his way diagonally up the hill.

George, on the other hand, made for some bush ahead of him, which looked
familiar, but in this he was disappointed, and going to the left,
considerably farther down the hill, was rewarded by the rediscovery of
the "hole." Without waiting he fired a shot, and to his surprise found
the Professor within a hundred feet.

"I have found it. See, that is the place I went through."

Harry was not far away, and he rushed up out of breath. The bushes were
swept aside and George went in, followed by the Professor and Harry. He
had not gone five feet when he stopped.

[Illustration: _Fig. 19. Fig. 20. Luxurious vegetation around stone and
hole._]

"This isn't the place. There is a big rock here; not a hole."

This was indeed the case.

George's countenance was a study. The Professor and Harry had a good
laugh at the discomfiture of George.

"So you think you fell into a hole? It must have been a pretty solid
hole." The rock was about ten feet across, and flat on top, and the bush
grew all around it, thus entirely screening it from observation.

"Well, we must try again."

"I would like to know why vegetation accumulates around a stone, or
around a hole, and gets so much larger than at other places?"

"It is accounted for by the little germs we talked about the other day.
Did you ever notice the musty smell that comes up from an overturned
stone?"

"Yes, and I have often wondered what it was."

"There is always more or less moisture under the stone, so that the
germs are readily bred, and as they form carbonic and nitrogenous gases,
which the plant must have, you can readily see why vegetation thrives
around the stones."

"But where there is a hole it is drier, and the same thing occurs
there?"

"That is a good observation. Two things are required to cultivate the
germs, aside from the food. One is moisture and the other is heat. The
earth is full of bacteria from which plants get their food; some places
the bacteria go down only one or two feet; at other places, where it is
warm, as in the tropics, they have been found five or six feet below the
surface. When a hole is made, and the sun strikes it, the bottom of the
hole gets warm, and thus facilitates the growth of the germs around the
hole, so that the plants in the immediate vicinity get an extra supply
of n