of. Johnston and
Sir Humphry Davy give instances in which more than fifteen per cent.
of ash was found; and Prof. Way gives cases where less than three
per cent. were obtained. The mean of forty samples was four and a
half per cent. Dr. Sprengel gives three and a half as the mean of
his analyses. M. Boussingault found an average of seven per cent. As
flint is truly the _bone_ of all the grass family, imparting to them
strength, as in cane, timothy, corn, oats, rye, rice, millet, and
the proportion of this mineral varies as much in wheat-straw, as
bone does in very lean and very fat hogs or cattle.

A young growing animal, whether a child or a colt, that is kept on
food which lacks _bone-earth_, (phosphate of lime,) will have soft
cartilaginous bones. Nature cannot substitute _iron_ or any other
mineral in the animal system, out of which to form hard strong
bones; nor can any other mineral in the soil perform the peculiar
function assigned to silica in the vital economy of cereal plants.
To protect the living germs in the seeds of wheat, corn, oats, rye,
barley, &c, the cuticle or bran of these seeds contains considerable
flint. The same is true of chaff.

The question naturally arises,--How is the farmer to increase the
quantity of soluble silica or flint in his soil? This is a question
of the highest practical importance. There are three principal ways
in which the object named may be attained. First, by keeping fewer
acres under the plough. Land in pasture, if well managed, will gain
its fertility, and in the process accumulate soluble silica in the
surface soil. In this way more wheat and surer crops may be made by
cultivating a field in wheat two years than four or six. If the
field in the mean time be devoted to wool-growing, butter or
cheese-making, or to stock-raising, particular care must be taken to
make great crops of grass or clover to grow on the land, and have
all the manure, both solid and liquid, applied to its surface.

There are many counties in England that yield an average of
thirty-two bushels of wheat per acre for ten crops in succession.
There are but few of the old counties in the United States which
average the half of that quantity: and yet America has greater
agricultural capabilities than that of Great Britain.

Another way to increase soluble silic