Section 40
SEC. 40. The lessee shall not assign, encumber, or sublet his rights without the consent of the Secretary of Agriculture and Commerce, and the violation of this condition shall avoid the contract: Provided, That assignment, encumbrance, or subletting for purposes of speculation shall not be permitted in any case: Provided, further, That nothing contained in this section shall be understood or construed to permit the assignment, encumbrance, or subletting of lands leased under this Act, or under any previous Act, to persons, corporations, or associations which under this Act, are not authorized to lease public lands.