treated; and in such cases the difference developed in the field is
just as marked as in the pot-cultures. In general we may set it down
as an absolute fact that the productive power of normal land depends
primarily upon the ability of the soil to feed the crop.

"I have here a photograph of a corn field on very abnormal soil.
They had the negative at the Experiment Station and I secured a
print from it, in part because I became interested in a story
connected with this experiment field, which our professor of soil
fertility reported to us.

"This shows a field of corn growing on peaty swamp land, of which
there are several hundred thousand acres in the swamp regions of
Illinois, Indiana, and Wisconsin. This peaty soil is extremely rich
in humus and nitrogen, well supplied with phosphorus and other
elements, except potassium; but in this element it is extremely
deficient. This land was drained out at large expense, and produced
two or three large crops because the fresh grass roots contained
some readily available potassium; but after three or four years the
corn crop became a complete failure, as you see from the untreated
check plot on the right; while the land on the left, where potassium
was applied, produced forty-five bushels per acre the year this
photograph was taken, and with heavier treatment from sixty to
seventy-five bushels are produced."

"Seventy-five bushels would be fifteen barrels of corn per acre.
How's that, Little Wife?" asked Tom.

"It's even more wonderful than the pot culture," replied Mrs.
Thornton; "but how much did the potassium cost, Mr. Johnston."