Post a form with Ajax to ASP.NET MVC Controller

When I click on the link "Foo", I hit the break point in the LogOn action but username is always null. I don't understand why.

<a class="jqselect" id="myId" href="#">Foo</a>    
@using (Html.BeginForm("LogOn", "Account", FormMethod.Post, new { id = "fooForm" }))
{
    <input type="text" id="username"/>
}

<script type="text/javascript">
    $(document).ready(function () {
        $(".jqselect").click(function () {

            $.ajax({
                url: '/Account/LogOn',
                type: "Post",
                data: $('#fooForm').serialize(),
                success: function (result) {
                    if (result.success) {
                    }
                }
            });

        });
    });
</script>

[HttpPost]
public ActionResult LogOn(string username)
{
    Console.WriteLine(username);
    return new EmptyResult();
}