effect on soil water, 156.
favors root growth, 14.
in fall, 99, 157.
in spring, 98, 157.
importance of deep, 15, 17.
objects of, 91, 92.
to save water, 92.
time for, 98.

Plows, 4.

Plumule, 78.

Pollen, 130.

Pollination, 131, 132, 135.
cross, 132, 133, 135.
of wild goose plum, 134.

Potash, 199.
in fertilizers, 199.
in soils, 149.
sources of, 171.

Potassium, in plants, 66, 67.
in soils, 68.

Potato, 6.
soils, 28, 29, 161.