251.340.  Adoption of plan. — The regional planning commission may adopt the comprehensive plan as a whole by a single resolution, or, as the work of making the whole comprehensive plan progresses, may by resolution adopt a part or parts thereof, any such part to correspond generally with one or more of the functional subdivisions of the subject matter of the plan.  The resolution shall refer expressly to the maps, plats, charts, programs and descriptive and explanatory matter, and other matters intended by the regional planning commission to form the whole or any part of the plan, and the action taken shall be recorded on the adopted plan or part thereof by the identifying signature of the chairman of the regional planning commission.