It would be erroneous to imagine that the colonies in the eighteenth century were in any way struggling, poverty-stricken communities. Their trade had grown with leaps and bounds, and they carried on a profitable commerce with England which Sir Robert Walpole had encouraged on the grounds that "the greater the prosperity of the colonies, the greater would be their demand for English goods."[213] That this proved true is shown by William Pitt saying in 1766, "the profits to Great Britain from the trade of the colonies are two millions a year. That was the fund that carried you triumphantly through the last war.... And shall a miserable financier come with a boast that he can filch a peppercorn into the exchequer to the loss of millions to the nation?"[214] For the same reason Adam Smith has given a conspicuous place to colonial trade in his _Wealth of Nations_. "Though the wealth of Great Britain," he writes, "has increased very much since the establishment of the Act of Navigation, it certainly has not increased in the same proportion as that of the colonies.... The industry of Great Britain, instead of being accommodated to a great number of small markets, has been principally suited to one great market.... The expectation of a rupture with the colonies accordingly has struck the people of Great Britain with more terror than they ever felt for a Spanish Armada or a French invasion."[215] The colonists did not, however, simply depend upon trade for their means of livelihood; many of them engaged in agriculture. During the winter months their beasts suffered as much as those in England, for until the eighteenth century there were no winter roots. In the same way the rotation of crops was much restricted, as the settlers were totally ignorant of artificial grasses. They had still to wait for Lord Townshend to make his agricultural experiments at home before they could grow turnips, cereals, and grasses on scientific principles. On the other hand they seem to have anticipated the discoveries of Mr Jethro Tull of Mount Prosperous, and some years previous to his work on husbandry they had inaugurated deep tillage. Tobacco, the principal commodity of the southern colonies, was not introduced into New England until 1660, but its place as a staple was taken by the cultivation of large quantities of rape, hemp, and flax. The colonists also, after many disappointments, came to be enthusiastic breeders of sheep, horses, goats, and cattle. At first the sheep fared very badly; the wool crop was short, and the climate proved unsuitable to the English stock. By 1642, however, there were one thousand sheep in Massachusetts, and these increased very rapidly. The authorities were most anxious to encourage sheep-farming, and in 1654 the exportation of sheep was forbidden. In Rhode Island and Connecticut they flourished upon the public lands, and by 1670 the latter colony was able to export a fairly large quantity of wool.