Mo. Rev. Stat. § 474.465: Failure of devise to become part of residue.

1. Except as provided in section 474.460, if a devise, other than a residuary devise, fails for any reason, it becomes a part of the residue.

2. Except as provided in section 474.460, if the residue is devised to two or more persons and the share of one of the residuary devisees fails for any reason, his share passes to the other residuary devisee, or to other residuary devisees in proportion to their interest in the residue.