Under such conditions rent is a differential which does not enter into the price of products; the marginal classes of land and soil qualities are worked free without paying rent. However, as soon as the demand increases and forces the marginal grades into the economic quantitative relation, a price must be allowed which leaves an excess, a rent, for those classes as well. Nevertheless, so long as there still remain reserves of uncultivated land, the increasing demand resulting in an extension of cultivation and its greater intensity will always bring it about that hitherto unused grades are taken under cultivation. These once more are free and used without paying rent. The prices of products are therefore stabilized at the costs of cultivating these lands.