being supported by the post; FIG. 5(d) is an enlarged plan view of the plate shown in FIG. 5(b); FIG. 5(e) is an enlarged fragmentary and perspective view of the plate shown in FIG. 5(d) secured to a shelf and the post; FIG. 6 is a plan, fragmentary and enlarged view of the first mounting bracket; FIG. 7 is a end elevational and fragmentary view of the first mounting bracket of FIG. 6; FIG. 8 is