ransplantation into the fields to the harvest.
This made it possible to grow two rice harvests instead of only one and
more than doubled the production. Rice varieties which grew again after
being cut and produced a second, but very much smaller harvest,
disappeared from now on. Furthermore, fish were kept in the ricefields
and produced not only food for the farmers but also fertilized the
fields, so that continuous cultivation of ricefields without any
decrease in fertility became possible. Incidentally, fish control the
malaria mosquitoes; although the Chinese did not know this fact, large
areas in South China which had formerly been avoided by Chinese because
of malaria, gradually became inhabitable.

The importance of alternating crops was also discovered and from now on,
the old system of fallow cultivation was given up and continuous
cultivation with, in some areas, even more than one harvest per field
per year, was introduced even in wheat-growing areas. Considering that
under the fallow system from one half to one third of all fields
remained uncultivated each year, the increase in production under the
new system must have been tremendous. We believe that the population
revolution which in China started about 1550, was the result of this
earlier agrarian revolution. From the eighteenth century on we get
reports on depletion of fields due to wrong application of the new
system.

Another plant deeply affected Chinese agriculture: cotton. It is often
forgotten that, from very early times, the Chinese in the south had used
kapok and similar fibres, and that the cocoons of different kinds of
worms had been used for silk. Real cotton probably came from Bengal over
South-East Asia first to the coastal provinces of China and spread
quickly into Fukien and Kwangtung in Sung time.

On the other side, cotton reached China through Central Asia, and
already in the thirteenth century we find it in Shensi in north-western
China. Farmers in the north could in many places grow cotton in summer
and wheat in winter, and cotton was a high-priced product. They ginned
the cotton with iron rods; a mechanical cotton gin was introduced not
until later. The raw cotton was sold to merchants who transported it
into the industrial centre of the time, the Yangtze valley, and who
re-exported cotton cloth to the north. Raw cotton, loosened by the
string of the bow (a method which was known since Sung), could now in
the north also be used fo