funkce $.get() neodesílá proměnné do php (jquery)

<?php
include_once("mysql_connect.php");
$prispivatel = $_SESSION['hero_jmeno'];
if(isset($_GET['pisi']))
{
  echo "ano";
  $writing = $_GET['pisi'];
  if($writing == "")
    mysql_query("UPDATE forum_users SET chat_writing = '0' WHERE username = '$prispivatel' LIMIT 1");
  else
    mysql_query("UPDATE forum_users SET chat_writing = '1' WHERE username = '$prispivatel' LIMIT 1");
}
else
  echo "ne";
$sql_write = mysql_query("SELECT username FROM forum_users WHERE chat_writing='1' ORDER BY username ASC");
echo "<span class='cas'>Právě píší uživatelé:</span><span class='prispivatel'>";
while($usrpisi = mysql_fetch_array($sql_write))
  echo " ".$usrpisi[0];
echo "</span>";
mysql_close($mysql_connection);
?>

...metadata, různej JS...
function refresh()
  {
      $.get('chat.vyhodnoceni.php', function(vystup){ if(document.getElementById('chatarea').innerHTML != vystup){ $('#chatarea').html(vystup); } } );
      $.get('chat.writing.users.php', { pisi: document.getElementById('textove_pole').value } );          // tahle proměnná se neodešle
      $.get('chat.writing.users.php', function(pisi){$('#writingusers').html(pisi); } );
      scrollDown();
  }
  setInterval("refresh();", 500);
</script>
...html stránky...
<form method="post">
<textarea id="textove_pole"></textarea><br />
<input type="button" value="Odeslat" onclick="odeslat(); reset();" /><br />
</form>
...další html a konec