Except as hereinafter provided, the assignment of any oil and gas lease issued under the provisions of sections 72-901 to 72-912, either in whole or in part, shall be permitted if made to an assignee qualified as provided herein. Such assignment shall not, however, be binding upon the state until filed with the Board of Educational Lands and Funds, accompanied by a filing fee of one dollar and a bond, and approved by the board, or its lawful representatives; Provided, that the approval of such assignment so filed and supported shall not be withheld in any case where satisfactory compliance has been made with the requirements of said sections. In no case shall the board be required to approve an assignment of a lease in part, covering a tract less than forty acres nor shall it be required to approve an assignment of an undivided interest in such lease until a showing, satisfactory to the board, has been made evidencing which one of the parties, assignor or assignee is to be the one to pay the delay rentals thereafter accruing, as to an undivided interest thereafter to be jointly owned, nor shall it be required to approve an assignment covering an undivided interest of less than forty leasehold acres.