There is by the State Securities Law, and there shall be by resolution authorizing the issuance of any indebtedness contracted in accordance with the provisions of the State Securities Law, specially appropriated the proceeds of such taxes to the payment of such principal and interest; and such appropriations shall not be repealed nor the taxes postponed or diminished (except as herein otherwise expressly provided) until the principal of and interest on the state securities evidencing such debt have been wholly paid.