什么是“只有ReactOwner可以具有引用”。意思？

我有一个react带有表单的简单组件：

var AddAppts = React.createClass({
    handleClick: function() {
        var title = this.refs.title.getDOMNode().value;
        ....

        var appt = {
            heading: title
            ...
        }

        CalendarActions.addAppointment(appt);
    },

    render: function() {
        return (
            <div>
                <label>Description</label>
                <input ref="title"></input>
                ...
            </div>
        );
    }
});
module.exports = AddAppts;

我正在尝试render在另一个react组件中使用此组件：

  var AddAppt = require('./AddAppts');

  render: function() {
    return (
      <div>
        <AddAppt />
      </div>
    );
  }

但是我得到这个错误：

 Uncaught Error: Invariant Violation: addComponentAsRefTo(...): Only a ReactOwner can have refs. This usually means that you're trying to add a ref to a component that doesn't have an owner (that is, was not created inside of another component's `render` method). Try rendering this component inside of a new top-level component which will hold the ref.

我已经用谷歌搜索了，但是无法弄清楚该问题的解决方法。