Appended Content Using JQuery 'append' Is Not Submitted?

I'm new to jQuery so this may be a real simple answer. I have a ASP.NET project that I'm trying to dynamically add content to an ASP Label element by typing into a text box and clicking a button. Sounds simple right? Well, I can get the content to added, but when the form is submitted the Label element is still empty? Why is the new data not submitted? Here's some sample code:

<asp:Label ID="lblContainer" Text="" runat="server" />
<input type="text" name="tag" id="tag" />
<input type="button" name="AddTag" value="Add" class="button" onclick="addTag();" />
function addTag() {
if ($("#tag").val() != "") {
$("#lblContainer").append('$("#tag").val()' + '<br />');
$("#tag").val("");
}
}