In the present century, of course, immigration has been largely shut off, so it is not surprising that this land-labor model, with labor mobile, no longer gives an adequate account of actual movements in factors and factor prices. What is surprising, it seems to me, is that capital movements do not perform the same functions. Within the United States, for example, we have seen southern labor move north to produce automobiles. We have also seen textile mills move from New England south to achieve this same end of combining capital with relatively low wage labor. Economically, it makes no difference which factor is mobile, so long as one is.