This point is not merely an academic one.  It means that we cannot explain the relative prices of cotton lint and cotton-seed in terms of cost at all, whether marginal or otherwise.  The influence of cost will be confined to the sum of the prices of the two things.  Upon this sum it will exert precisely the same influence as it exerts upon price in general, by affecting the total quantities of the two things that will be supplied.  But upon the distribution of this sum between lint and seed, cost will exert no influence whatever, because it cannot affect the proportions in which they are supplied.  It may assist some readers if I state the matter in more concrete terms.  Cost of production will be one of the factors which will result in the production of an annual cotton crop in the United States of, let us say, 10 million tons of seed cotton.  This crop will yield roughly 6-2/3 million tons of cotton-seed, and 3-1/3 million tons (or rather more than 13 million bales) of lint.  The combined price received by the planter of (let us say) 14.4 cents for 1 pound of lint plus 2 pounds of seed should correspond roughly to the marginal joint costs of production.  But the factor of cost has no influence at all in determining that this combined price is made up of a price of 12 cents per pound for lint, and only 1.2 cents per pound (or $24 per ton) for cotton-seed.  To account for this we must rely entirely upon demand.  We can say, shortly, that the respective prices must be such as will enable the demand to carry off 6-2/3 million tons of seed, and 3-1/3 million tons of raw cotton.  Or we can go further and say that the marginal utility of a pound of raw cotton, when 3-1/3 million tons are supplied, is ten times as great as that of a pound of seed when 6-2/3 million tons are supplied.

If accordingly the demand for cotton-seed were to expand considerably owing, say, to the discovery of some new use for the oil, which is its most valuable constituent; the effect would be first a rise in the price of cotton-seed, and, subsequently, by stimulating cotton growing, a more plentiful supply and a lower price for raw cotton.  And so far at least as the increased supply is concerned, this must necessarily be the effect, “other things being equal”; though, to be sure, it might be outweighed and obscured by other influences such as the boll-weevil.  But it is not the case that an increased demand for mutton must necessarily increase the supply or lower the price of wool; and it is most unlikely to do so in any similar degree.  For, here, the separate marginal costs of the two things exert their influence.  An increased demand for mutton will stimulate sheep farming, but it will also stimulate the substitution of crossbred for merino breeds; and the resultant of these two opposite tendencies upon the supply of wool is logically indeterminate.  As a matter of history we know that the development of cold storage in the eighties (which we may regard for the present