No public utility corporation shall purchase or acquire, take or hold, any part of the capital stock of any other public utility corporation, organized or existing under or by virtue of the laws of the State, without having been first authorized to do so by the order of the public utilities commission. Every assignment, transfer, contract, or agreement for assignment or transfer of any stock by or through any person or corporation to any corporation or otherwise in violation of this section shall be void and of no effect; and no such transfer shall be made on the books of any public utility. Nothing herein shall be construed to make illegal the holding of stock lawfully acquired before July 1, 1933.