The trustees shall have power to prescribe all needful rules and regulations for the government of said cemetery. The trustees shall set aside a part of the purchase price of each burial lot sold, for the permanent maintenance of said cemetery, to be invested in any of the investments authorized by the provisions of section 30-3201. No part of the principal of this fund shall be used except for investment purposes as aforesaid. Each investment shall be approved by the unanimous vote of the board of trustees and entered upon the records of Wyuka Cemetery. The trustees shall appoint a treasurer to have custody of its funds who shall give a surety company bond in a sum not less than the amount of cash in his hands, conditioned for the safekeeping of such funds.