"What, then, do these shoals of creatures live upon?"
"The big ones upon the little ones; fish devour each other."
"A beautiful harmony of Nature," remarked Fritz drily.
"Then plants," continued Jack, "are still more prolific than animals. Some trees can produce as many of their kind as they have branches, or even leaves. An elm tree, twelve years old, yields sometimes five hundred thousand pods; and, by the way, Willis, to encourage you in carrying on the war against the mosquitoes, a single stalk of tobacco produces four thousand seeds."
"The leaves, however, are of more use to me than the seeds," replied Willis.
"This admirable proportion between the productiveness of the two kingdoms demonstrates the far-seeing wisdom of Providence. If the power of multiplication in vegetables had been less considerable, the fields, gardens, and prairies would have been deserts, with only a plant here and there to hide the nakedness of the land. Had God permitted animals to multiply in excess of plants, the entire vegetation would soon have been devoured, and then the animals themselves would of necessity have ceased to exist."
"How is it, then," inquired Willis, "with this continual multiplication always going on, the inhabitants of land and sea do not get over-crowded?"
"Why, as regards man, for example, if thirteen or fourteen human beings are born within a given period, death removes ten or eleven others; but though this leaves a regular increase, still the population of the globe always continues about the same."
"It may be so, Master Jack, but when I was a little boy at school, I generally came in for a whipping, if I made out two and two to be anything else than four."
"And served you right too, Willis; but if the human family did not continually increase, if the number of deaths exceeded continually that of the births, at the end of a few centuries the world would be unpeopled."