How to retrieve values from TextArea in a Local Variable in ASP MVC

I am developing an ASP .Net MVC 3 application using C# and SQL Server 2005.

In a view, I have 2 DropDownList and TextArea and 2 buttons :

• DropDownList Poste
• DropDownList Fonction
• Button Ajouter
• Button Enregistrer
• TextArea

The Values of the TextArea are added from the DropDownList 'Fonction' when I click on the button 'Ajouter'.

I want to retrieve those values in a local variable. And that when the user click on the button 'Enregistrer'(submit).

This is the code of the view :

<% using (Html.BeginForm("Store", "Fonction")) { %>
<h2>Gérer les droits</h2>
 <form id="form1" runat="server">
<fieldset><legend>Gestion</legend>

        <div>
        <%:Html.Label("Poste :")%><%: Html.DropDownListFor(model => model.SelectedPoste, Model.PostesItems)%>
        </div>
        <br />
        <div>
        <%:Html.Label("Fonction :")%><%: Html.DropDownListFor(model => model.SelectedFonction, Model.FoncItems, new { @id = "ff" })%>
        </div>
        <br />
        <div><input type="button" value="Ajouter" id="aj"  onclick="addtext()"/></div>
        <br />
        <div>
        <textarea id="tt" cols="10"  name="S1" rows="8" readonly="true"></textarea>
        </div>
</fieldset>
<br />
<div><input type="submit" value="Enregistrer" id="sv" /></div>
</form>

<script language="javascript" type="text/javascript">
    var storedValues = [];
    function addtext() {

        var ff = document.getElementById('ff');
        var tt = document.getElementById('tt');


        var selectedValue = ff.options[ff.selectedIndex].value + " ";
        if (storedValues.indexOf(selectedValue) === -1) {
            storedValues.push(selectedValue)
            tt.value = storedValues.join('')
        }

    }
</script>

and this is the code of the methode store (for the submit) in the controller :

 [HttpPost]
        public ActionResult Store(FlowViewModel model)
        {

            if (ModelState.IsValid)
            {

                Fonction_Poste FP = new Fonction_Poste();
                FP.ID_Poste = model.SelectedPoste;
                FP.ID_Fonction = model.SelectedFonction;
                FP.Droit = 1;

                System.Web.UI.HtmlControls.HtmlTextArea htaDemo = (System.Web.UI.HtmlControls.HtmlTextArea)(form1.FindControl("tt"));
                String Value = htaDemo.Value;

                db.Fonction_Postes.Add(FP);
                db.SaveChanges();

            }
            return RedirectToAction("Index");
        }

So as you see, Itried to do retrive values using this statement but that's didn't give any result :

System.Web.UI.HtmlControls.HtmlTextArea htaDemo = (System.Web.UI.HtmlControls.HtmlTextArea)(form1.FindControl("tt"));
            String Value = htaDemo.Value;