Section 4A. The commonwealth, acting through one or more state departments, and any city, town or district, or any combination thereof, to the extent of their ownership of any area described in section one, may be parties, in their proprietary capacity, to proceedings under sections one to fourteen C, inclusive, in respect to any purpose set forth in said section one, to the same extent as individual proprietors. Said bodies politic, or any combination thereof, may also institute proceedings under said sections in their governmental capacity, in any case where it appears that the public health, safety or convenience will be promoted by improvements to effect any of said purposes, but in such proceedings no district shall be organized, and the improvements shall be constructed and maintained as provided in section five A. The petition in such a proceeding need cover only matters pertinent to the project therein set forth, and the provisions of section five requiring that the petitioners constitute a majority ownership of the lands affected shall not apply to such petition. Individuals and corporations qualifying as proprietors may join in any petition authorized in this section. Action by any such body politic hereunder shall be taken by the administrative head of the state department or commission, or by the mayor, selectmen, or prudential committee or other governing body, as the case may be. Notice of the hearing before said board on such a petition shall be given as provided in the first paragraph of section five to all petitioners and to the administrative heads of such state departments and commissions, mayors of such cities, selectmen of such towns, and the prudential committees or other governing bodies of such districts, as the said board may determine, and to all other known proprietors of lands to be affected by such improvements. Cities, towns and districts are hereby authorized to raise and appropriate money for such purposes.