Rent does not really form any part of the expenses of [agricultural] production, or of the advances of the capitalist. The grounds on which this assertion was made are now apparent. It is true that all tenant-farmers, and many other classes of producers, pay rent. But we have now seen that whoever cultivates land, paying a rent for it, gets in return for his rent an instrument of superior power to other instruments of the same kind for which no rent is paid. The superiority of the instrument is in exact proportion to the rent paid for it. If a few persons had steam-engines of superior power to all others in existence, but limited by physical laws to a number short of the demand, the rent which a manufacturer would be willing to pay for one of these steam-engines could not be looked upon as an addition to his outlay, because by the use of it he would save in his other expenses the equivalent of what it cost him: without it he could not do the same quantity of work, unless at an additional expense equal to the rent. The same thing is true of land. The real expenses of production are those incurred on the worst land, or by the capital employed in the least favorable circumstances. This land or capital pays, as we have seen, no rent, but the expenses to which it is subject cause all other land or agricultural capital to be subjected to an equivalent expense in the form of rent. Whoever does pay rent gets back its full value in extra advantages, and the rent which he pays does not place him in a worse position than, but only in the same position as, his fellow-producer who pays no rent, but whose instrument is one of inferior efficiency. Soils are of every grade: some, which if cultivated, might replace the capital, but give no profit; some give a slight but not an ordinary profit; some, the ordinary profit. That is, “there is a point up to which it is profitable to cultivate, and beyond which it is not profitable to cultivate. The price of corn will not, for any long time, remain at a higher rate than is sufficient to cover with ordinary profit the cost of that portion of the general crop which is raised at greatest expense.”(188) For similar reasons the price will not remain at a lower rate. If, then, the cost of production of grain is determined by that land which replaces the capital, yields only the ordinary profit, and pays no rent, rent forms no part of this cost, since that land does not and can not pay any rent. McLeod,(189) however, says it is not the cost of production which regulates the value of agricultural produce, but the value which regulates the cost. BOOK III. EXCHANGE. Chapter I. Of Value. § 1. Definitions of Value in Use, Exchange Value, and Price.