Section 3. Seven or more persons, residents of the commonwealth, may associate themselves as a corporation, association, society, company or exchange, to conduct within the commonwealth any agricultural, dairy or mercantile business on the co-operative plan. The word ''co-operative'' shall form a part of the name of the corporation, and, for the purposes of this and sections three A to nine, inclusive, the words ''association'', ''company'', ''exchange'', ''society'' and ''union'', shall have the same signification and shall import a corporation. The corporation shall be formed as provided in chapter one hundred and fifty-six B, with shares having par value, and shall be subject to the provisions thereof so far as consistent with said sections.