The Legislature of the State of Oklahoma is hereby authorized to enact a law whereby the State may become indebted in an amount not to exceed Thirty-six Million Dollars ($36,000,000.00) for the purpose of constructing, equipping, remodeling and repairing any and all buildings of the State, including those of its educational, recreational, penal and eleemosynary establishments; and such law shall provide that two cents (2¢) of the tax on each package of cigarettes authorized by 68 O.S.1941, Par. 586 to 586p, as amended and supplemented to the effective date of this Section, or so much of said tax as may be necessary, shall be pledged and used for the sole purpose of paying the interest on such debt as it falls due, and also to pay and discharge the principal of such debt within twenty-five (25) years from the time of the contracting thereof; provided, that if said tax is not sufficient to so pay and discharge said interest and principal, the Legislature shall impose and provide for the collection of an additional tax, other than an ad valorem tax, sufficient to pay and discharge said interest and principal.