Section 50. Notice of a petition under the preceding section shall be given in such manner as the court may order to all persons who are or who may become interested in the land to which the petition relates, and to all persons whose issue, not in being, may become interested therein; and the court shall of its own motion in every case appoint a suitable person to appear and act therein as the next friend of all minors, persons not ascertained, and persons not in being, who are or may become interested in such land; and provisions of sections thirty-four and thirty-five of chapter two hundred and one consistent herewith shall apply in the case of such appointment.