509.510. Upon motion of a party the court may, uponreasonable notice and upon such terms as are just, permit him toserve a supplemental pleading setting forth transactions oroccurrences or events which have happened since the date of thepleading sought to be supplemented. If the court deems itadvisable that the adverse party plead thereto, it shall soorder, specifying the time therefor.
(L. 1943 p. 353 ยง 83)