Share Session between a Codeigniter Subdomains and Other in Pure PHP

I have a two subdomain (one.mismodomino.com and two.mismodomino.com) the first is done in PHP call it "Pure" and the other is done in Codeigniter, both work normally but I want to share a session between both subdomains for example the $ _SESSION ['names'] or $ this- > session-> userdata ('names') is accessible from both codeigniter and PHP.

Achieved so far:

In codeigniter I have the native sessions of php $ _SESSION ['names'] or $ this- > session-> userdata ('names') give me the same result, it's more in a third subdomain echo in codeigniter a test mode "tres.mismodomino.com", if you read the session of the other made in codeigniter, but PHP Puro does not recognize them.

Codeigniter Config Code of two.mismodominio.com

$config['sess_driver'] = 'files';
$config['sess_cookie_name'] = 'ci_session';
$config['sess_expiration'] = 7200;
$config['sess_save_path'] = NULL;
$config['sess_match_ip'] = FALSE;
$config['sess_time_to_update'] = 300;
$config['sess_regenerate_destroy'] = FALSE;

$config['cookie_prefix']    = '';
$config['cookie_domain']    = '.mismodominio.com';
$config['cookie_path']      = '/';
$config['cookie_secure']    = FALSE;
$config['cookie_httponly']  = FALSE;

In the cController of uno.mymodomain.com

public function cargaVariable(){
    $this->session->set_userdata('nombre',"Alex");
    $_SESSION['nombres']="Alexander";
}

On the PHP page in one.mymodomain.com

session_name('ci_session');
ini_set('session.cookie_domain', '.mismodomino.com' );
session_start();
echo "Aqui abajo debe Mostrar algo<br>";
echo $_SESSION['nombres'];
echo $_SESSION['nombre'];

In PHP's it does not print anything. Thank you in advance for your support.

(By the way, you can not pass the PHP to codeigniter (It's another module))