Accessing angular bootstrap modal form from controller

I am trying to access the form from the modal controller (Plunkr) but myForm doesn't seem to be accessible. How to get alert call to work:

angular.module('plunker', ['ui.bootstrap']);
var ModalDemoCtrl = function ($scope, $modal, $log) {
  $scope.open = function () {
    var modalInstance = $modal.open({
      templateUrl: 'myModalContent.html',
      controller: ModalInstanceCtrl          
    });       
  };
};

var ModalInstanceCtrl = function ($scope, $modalInstance) {
  $scope.submit = function() {
    // How to get this?
   alert($scope.myForm.$dirty);
  };

  $scope.ok = function () {
    $modalInstance.close();
  };

  $scope.cancel = function () {
    $modalInstance.dismiss('cancel');
  };
};

And template:

<div ng-controller="ModalDemoCtrl">
    <script type="text/ng-template" id="myModalContent.html">
        <div class="modal-header">
            <h3>I'm a modal!</h3>
        </div>
        <div class="modal-body">
          <form name="myForm" novalidate>
          <input type="email" value="hello">
          </form>
        </div>
        <div class="modal-footer">
            <button class="btn btn-primary" ng-click="submit()">OK</button>
            <button class="btn btn-warning" ng-click="cancel()">Cancel</button>
        </div>
    </script>

    <button class="btn" ng-click="open()">Open me!</button>
    <div ng-show="selected">Selection from a modal: {{ selected }}</div>
</div>