Most of the criticism of the Marxian theory of concentration is based upon a very unsatisfactory definition of what is meant by concentration. The decrease of small units and their absorption or supercession by larger units is generally understood when concentration is spoken of. But concentration may take other, very different forms. There may be a concentration of _control_, for example, without concentration of actual ownership, or there may be concentration of actual ownership disguised by mortgages, as already suggested. The sweated trades are a familiar example of the former method of concentration. It has been shown over and over again that while small establishments remain a necessary condition of sweated industry, there is almost always effective concentration of control. To all appearances an independent manufacturer on a small scale, the sweater is generally nothing more than the agent of some big establishment, which finds it more economical to let the work be done in sweatshops than in its own factories. The same thing holds good of the retail trades, many of the apparently independent retail stores being simply agencies for big wholesale houses, controlled by them in every way. In an even larger measure, agriculture is subject to a control that is quite independent of actual or even nominal ownership of the farm. Manifestly, therefore, we need a more accurate and comprehensive definition of concentration than the one generally accepted. Mr. A. M. Simons, in an admirable study of the agricultural question from the Socialist viewpoint, defines concentration as "a movement tending to give a continually diminishing minority of the persons engaged in any industry, a constantly increasing control over the essentials, and a continually increasing share of the total value of the returns of the industry."[105] It is no part of the purpose of this chapter to discuss this definition at length. It is sufficient to have thus emphasized that concentration may be quite as effective when it is limited to control as when it embraces ownership.