Getting value from <tr>.

Getting value from <tr>.

Hi all,
I need help to get value from <tr>.
This is my html table. I want to get the value of textarea.

<table>
      <tr>
        <th>Cognome            </th>
        <th>Nome                </th>
        <th>Data di nascita    </th>
        <th>Mail genitore      </th>
        <th>Cellulare genitore </th>
      </tr>
      <tr> 
        <td><?php echo $r_agenda['CognomeStudente']        ?></td>  
        <td><?php echo $r_agenda['NomeStudente']           ?></td>
        <td><?php echo $nascita                            ?></td>
        <td><?php echo $r_agenda['MailGenitore']           ?></td>
        <td><?php echo $r_agenda['CellStudente']           ?></td>
      </tr>
      <tr>
        <td colspan="5">
              
   <textarea id="nAgenda" style="height:100px; width:450px;" ></textarea>
         </td>
         </tr>
         </table>   

Thanks in advance.

Tegatti