averaged thirty-seven bushels for the same fifty years."

"The same kind of wheat?" inquired Mr. Thornton.

"Yes, and great care has always been taken to have these two plots
treated alike in all respects, save one."

"And what was that?"

"Plant food was regularly incorporated with the plowed soil of the
high-yielding plot."

"You mean that farm manure was used?"

"No, not a pound of farm manure has been used on that plot for more
than sixty years; and, furthermore, the two plots were very much
alike at the beginning; but, to the high-yielding plot, nitrogen,
phosphorus, potassium, magnesium, calcium, and sulfur have all been
applied in suitable compounds every year."

"That is to say," observed Mr. Thornton, "that the land itself has
produced thirteen bushels of wheat per acre and the plant food
applied has produced twenty four bushels, making the total yield
thirty-seven bushels on the fertilized land."

"That is certainly a fair way to state it," replied Percy.

" Well, that sounds as though something might be done with run-down
lands. About what part of the twenty-four bushels increase would it
take to pay for the fertilizers?"