It shall be lawful for the Corporation of Oamaru to lease to any person or body corporate all or any portion of the land aforesaid, for any period not exceeding twenty-one years, and at any rental which the said Corporation may see fit, or at a nominal rental, upon such conditions as to the said Corporation shall seem right, for the purpose of establishing a corn exchange on such parcel of land:
Provided always that the said Corporation shall reserve a sufficient part of such land for the purposes of a public market, or the lessees shall be bound to provide for the use of part of the said land for that purpose; and such lease may contain a covenant to renew for a further term of not more than twenty-one years.