The Secretary of the Interior is authorized in his discretion to accept title to lands tendered without cost to the United States within the area of the Mammoth Cave National Park, subject to leases entered into and granted as part consideration in connection with the purchase of said land for tender to the United States for park purposes, but not exceeding in length of term the life of the particular grantor or grantors: Provided, That said leases and the terms and conditions thereof shall have previously been submitted to and approved by said Secretary: And provided further, That he may lease upon such terms and conditions as he deems proper any lands within the aforesaid areas when such use shall not be deemed by him inconsistent with the purposes for which the lands were acquired on behalf of the United States, to persons, educational or religious institutions, private corporations, associations, and partnerships previously occupying such land for terms not exceeding the particular lifetime in the case of natural persons, and not exceeding twenty years in all other cases, which latter leases may be renewed in the discretion of said Secretary: And provided further, That the Secretary of the Interior may accept lands for these parks subject to reservations of rights-of-way and easements.