Section 121. No land originally acquired in any manner under the provisions of the former Public Land Act or of any other Act, ordinance, royal order, royal decree, or any other provision of law formerly in force in the Philippine Islands with regard to public lands, terrenos baldios y realengos, or lands of any other denomination that were actually or presumptively of the public domain, or by royal grant or in any other form, nor any permanent improvement on such land, shall be encumbered, alienated, or conveyed, except to persons, corporations, or associations who may acquire land of the public domain under this Act; to corporate bodies organized in the Philippine Islands whose charters may authorize them to do so, and, upon express authorization by the Philippine Legislature, to citizens of the countries the laws of which grant to citizens of the Philippine Islands the same right to acquire, hold, lease, encumber, dispose of, or alienate land or permanent improvements thereon or any interest therein, as to their own citizens, and only in the manner and to the extent specified in such laws, and while the same are in force, but not thereafter: Provided, however, That this prohibition shall not be applicable to the conveyance or acquisition by reason of hereditary succession duly acknowledged and legalized by competent courts, nor to lands and improvements acquired or held for industrial or residence purposes, while used for such purposes: Provided, further, That in the event of the ownership of the lands and improvements mentioned in this section and in the last preceding section being transferred by judicial decree to persons corporations or associations not legally capacitated to acquire the same under the provisions of this Act, such persons, corporations, or associations shall be obliged to alienate said lands or improvements to others so capacitated within the precise period of five years, under the penalty of such property reverting to the Government in the contrary case.