d the importance of tillage
operations by putting forward a theory to account for the fact,
universally recognised, that the more thoroughly a soil was tilled, the
more luxuriant the crops would be. As Tull's theory had a very
considerable influence in stirring up interest in many of the most
important problems in agricultural chemistry, and as it contained in
itself much, the value of which we have only of late years come to
understand, a brief statement of this theory may not be without
interest.

According to Tull the food of plants consists of the particles of the
soil. These particles, however, must be rendered very minute before they
become available for the plant, which absorbs them by means of its
rootlets. This pulverisation of the soil goes on in nature independently
of the farmer, but only very slowly, and the farmer has therefore to
hasten it on by means of tillage operations. The more efficiently these
operations are carried on, the more abundant will the supply of
plant-food be rendered in the soil. He consequently introduced and
advocated the system of horse-hoe husbandry. This theory, he informs us,
was suggested to him by the custom, which he had noticed on the
Continent, of growing vines in rows, and hoeing the intervals between
these rows from time to time. The excellent results which followed this
mode of cultivation induced him to adopt it in England for his farm
crops. He accordingly sowed his crops in rows or ridges, wide enough
apart to admit of thorough tillage of the intervals by ploughing as well
as by hand-hoeing. This he continued until the plant had reached
maturity. As to the exact width of the interval most suitable, he made a
large number of experiments. At first, in the cultivation of wheat, he
made this interval six feet wide; but latterly he adopted an interval of
lesser width, that finally arrived at being between four and five feet.
He likewise experimented on each separate ridge as to which was the best
number of rows of wheat to be sown, latterly adopting, as most
convenient, two rows at ten inches apart. The great success which he met
with in this system of cultivation induced him to publish the results of
his experiments in his famous work, 'Horse-Hoeing Husbandry.'

While Tull's theory was based on principles at heart thoroughly sound,
he was carried away by his personal success into drawing unwarrantable
deductions. Thus he came to the conclusion that rotation of crops was
u