For the purpose of making capital improvements in connection with botanical gardens, the corporate authorities of the forest preserve district in which such gardens are maintained may incur an indebtedness and issue bonds therefor in amounts not exceeding in the aggregate $32,000,000. Such bonds shall bear interest at not more than the maximum rate provided by law and shall mature within 20 years from the date thereof. The resolution authorizing this issuance of bonds may be made effective without the submission thereof to the voters of the district for approval.
     All moneys received from the issuance of bonds as provided in this Section shall be set apart in a separate fund by the district treasurer and shall be used only for the purposes set forth in this Section.
     The corporate authorities of such district shall provide for the levy of a direct annual tax upon all the taxable property in such district, sufficient to pay and discharge the principal of such bonds at maturity and to pay the interest thereon as it falls due. This tax shall be levied and collected in like manner with the general taxes of the forest preserve district and shall be in addition to the maximum of all other taxes and tax rates which the district is or may be authorized to levy.