The Oklahoma Historical Society may solicit and receive contributions, gifts, and donations to be held by it in trust under the terms and conditions imposed by the donors, and title to all real estate acquired, donated and granted to said Society shall be taken in the name of the state to be held for the use and benefit of the Oklahoma Historical Society under the conditions of such grants or donations, the Board of Directors of the Oklahoma Historical Society, through its officers or duly authorized agents to be manager of such real property with authorization to let and lease the same for a period not to exceed three (3) years, and where necessary employ a suitable custodian or custodians of such realty, with the proviso that no expense is to be incurred relative thereto except as is authorized by law and an appropriation theretofore made to meet same. Provided, further, that as to such realty as may consist of parks and places of historical interest with buildings thereon such custodian or caretaker may be employed by such Board to be paid out of receipts from visitors or out of an appropriation theretofore specifically made for such purpose, and from donations theretofore pledged for such purpose and made to meet such expense, which is not to exceed such receipts or donations or such appropriation theretofore made for such purpose.