mful, exposing the soil to the sun and robbing it
of moisture. When winter comes, there should be sufficient grass to
serve as a mulch to the roots. It acts like a coat of manure, giving
new life to the plants the next spring. Good sods are not easily or
quickly made, and when they have been secured on land unfit for the
plow, their value measures the value of the land itself.

CHAPTER X

THE COWPEA

A Southern Legume.--The soils of the cold north are protected from
leaching during the winter by the action of frost. The plant-food is
locked up safely for another year when nature ceases her work of
production for the year. Farther south, in the center of the corn belt,
there are leaching periods in fall and spring and oftentimes during the
winter, but winter wheat thrives and, in ordinary crop-rotations,
covers much of the land that might otherwise lose plant-food. As we
pass from the northern to the southern states, the preservation of soil
fertility grows more difficult and at the same time the restoration of
humus becomes easier. The heat makes easy the change of organic matter
to soluble forms, and the rains cause waste, but the climate favors
plants that replace rapidly what is lost. In the work of supplying land
with fertility, directly and indirectly, the southern cowpea has an
important place. It is to the south what red clover is to the north,
and it overlaps part of the red-clover belt, having a rightful place as
far north as the Ohio Valley, and portions of Pennsylvania.

Characteristics.--The cowpea is closely related to the bean, and is
very unlike the Canada pea, which is a true pea, thriving only in a
cool climate. The cowpea has been grown in the southern states over one
hundred years, and the acreage is large, but it never has come into the
full use it deserves. Being a legume, it stores up nitrogen taken from
the air, and unlike red clover it makes its full growth within a short
period of time. It can grow on land too infertile for most kinds of
valuable plants, and on better land. The vines can crowd out nearly all
varieties of weeds. The roots go to a good depth and are thickly
covered with the nodules of nitrogen-gathering bacteria.

Varieties.--There are many varieties of the cowpea, and confusion of
names prevails, although some stations have done good service in
identification of individuals carrying a number of names. The very
quick-maturing varieties adapted to northern conditions d