A greater incentive to settlement than free land was the discovery of a crop that could be exported at a profit. Virginia had been founded to raise silk and tropical products, and to supply England with naval stores. But the difficulties were greater than had been anticipated, and in 1616, when John Rolfe, having discovered a superior method of curing the leaf, sold a cargo of native tobacco in London at a profit, the future of Virginia was assured. Neither the plans of the company nor the scruples of the king could prevail against the force of economic self-interest. Twenty thousand pounds were exported in 1619, forty thousand in 1622, sixty thousand in 1624. Tobacco became at once, and in spite of long opposition on the part of the home Government remained, the chief enterprise of the colony. Virginia was founded on tobacco, and like the other Southern colonies, sacrificed everything to the raising of her most important commodity; and for Virginia, as for the other Southern colonies, the conditions necessary for the cultivation of her great staple were of determining influence in the development of her social institutions. Those who were interested in the Virginia Company loudly proclaimed that the recall of the charter would ruin the colony. But it was population, rather than corporate or royal control, that Virginia needed, and the profits from tobacco proved a more powerful incentive to large families and immigration than all the efforts of king or company. Within a decade after 1624 the number of settlers increased from 1232 to 5000. In 1649 the population had reached 15,000, and in 1670 it stood at 38,000. Land was virtually free to those who could pay for the cost of clearing, and the rich soil of the tide-water bottoms assured an easy living and the prospect of accumulating a competence. As the conditions of life grew easier, the Virginians, with the true instinct of frontiersmen, described America as God's country, abounding in every good thing: "Seldom any that hath continued in Virginia any time will or do desire to live in England, but put back with what expedition they can." The glowing accounts which reached England appealed to those of every class whose straitened circumstances or unsatisfied ambitions disposed them to a hazard of new fortunes. The yeoman farmer, whose income was small and whose children would always remain yeomen; the lawyer and the physician, the merchant and the clergyman, ambitious to become landowners and play the gentleman; younger sons of the country gentry, for whom there were no assured avenues of advancement: these felt the call of the New World. Fretted by social restrictions, or pinched by rising standards of living, they saw Virginia in the light of their ideals, and were willing to exchange a safe but restricted position for the chance of economic and social enfranchisement.