"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 nitrogen."
"But where do they get the moisture?"
"That is another one of nature's great surprises, and shows how every contingency seems to be provided for. I suppose you have both cultivated corn—that is, have gone between the rows with a cultivator, and stirred up the earth. You did this, as you were told, to keep down the weeds. That was one reason, but it is not the principal one. A dry crust forms over the surface of the ground, owing to the heat of the sun. When the cultivator breaks up the crust the heat from the sun draws up the moisture from below, and you are therefore watering your corn, and what is more, you are breeding bacteria so as to supply food for the plants."