Opportunities for new methods of cultivation were afforded by the leasing of the demesne to a single farmer, which would lead us to look at his holding as the place where agrarian changes were most likely to begin, and to start from that in order to trace the effect of these large properties on the small properties of the customary tenants. On the one hand, any wide development of leasehold tenure involves a certain mobility in rural society and a disposition to break with routine. There must be a market for land, which again implies that some class has accumulated sufficient capital to invest and has got beyond mere subsistence farming. It naturally arises either when new[401] land is brought into cultivation, or when the development of trade makes farming for the market profitable, or when changes are being introduced into the methods of agriculture, or when the value of land is uncertain (for example, when it is thought that it may contain minerals),[402] because in all these cases leasehold, being a terminable interest, enables the owner of land to adjust his rent to the tenant's returns. On the other hand, the landowner does not get the full advantage of the elasticity in rent and management that leasehold tenure makes possible, unless the tenant is a man of some substance, who can spend capital in cultivating land on a large scale, in stocking a farm with sheep and cattle, in carrying crops until the best market is found, and in making experiments in new directions.
[402] See _Northumberland County History_, vol. ix., account of Cowpen, and _Victoria County History_, Lancashire, article on Social and Economic History. For the same reasons mills and fisheries were naturally the first parts of a mediæval manor to be leased for terms of years.