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.