Pre-emption rights in property depend on contractual contingency and are enforceable only by suit, not by will. Pre-emption claims create an interest in the specific property, enforceable upon the contingency specified by agreement and by suit; a will does not effect transfer to enforce contractual pre-emption. Pre-emption based solely on consanguinity has been criticized as antiquated and, where statutory classifications of entitled kinsfolk are unreasonable, as inconsistent with constitutional non discrimination and property guarantees.