Section 12. Boulevard—Proceedings to Improve. the Board of Park

commissioners of any such city shall have the power to order the improvement of any boulevard or any pleasure driveway or part thereof, under the control of such board, by paving the same, curbing and constructing sidewalks thereon, or either paving, curbing and constructing sidewalks thereon in the same manner and subject to the same limitation as to form and procedure, and to the same extent as is or may be in the future conferred upon the board of public works of any such city to improve any street, alley or sidewalk within such city; the cost of such improvement of such boulevard or pleasure driveway shall become a lien upon property to the same extent, enforceable in the same manner, with the same rights as to payments by installments and appeal as are or may be provided for in the case of street and sidewalk improvements ordered by the board of public works; and the provisions of said laws applicable to street and sidewalk improvements ordered by the board of public works of any such city are hereby extended to the improvement of any such boulevard, or pleasure driveway: Provided, That said board shall have exclusive authority to determine the kind of pavement to be used. And said park board shall have the power to change and fix the grade of any boulevard, park boulevard, or public driveway, or public ground under its control, to the same extent as such power is now or may be in the future conferred upon the board of public works of any such city to change and fix the grade of any street, alley or public place within any such city: Provided, That whenever the land along one side of a boulevard or pleasure driveway is owned by the city or used by the city for park purposes, one-half the cost of such improvement may be assessed against the property benefited in such park district, or districts, to the extent and in the proportion the same shall be benefited as hereinafter provided; and in case it should be determined by said board that no part of the cost of such improvement is properly assessable against the property of a district, or districts, in which the improvement is made, the same may be paid by such city out of any funds available for such purposes.