509.490. A party may amend his pleading as a matter ofcourse at any time before a responsive pleading is filed andserved, or, if the pleading is one to which no responsivepleading is required and the action has not been placed upon thetrial calendar, he may so amend it at any time within thirty daysafter it is filed. Otherwise a party may amend his pleading onlyby leave of court or by written consent of the adverse party; andleave shall be freely given when justice so requires. A partyshall plead in response to an amended pleading within the timeremaining for response to the original pleading or within tendays after service of the amended pleading, whichever period maybe the longer, unless the court otherwise orders.
(L. 1943 p. 353 ยง 81)