For the purpose of meeting disbursements for pensions, annuities, and other payments, cash may be kept available on deposit in one or more banks or trust companies organized under the laws of this state or of the United States, provided that the sum on deposit in any one bank or trust company shall not exceed 25 percent of the paid up capital and surplus of each bank or trust company; and provided, further, that each bank or trust company shall either give a depository bond in an amount sufficient to cover the deposits or place in trust a sufficient amount of federal or state securities to cover the deposits.