问CodeIgniter会话set_flashdata不工作

EN

<?php
class Home extends CI_Controller{
    public function __construct(){
        parent::__construct();
        $this->load->helper(array('url','form');
        $this->load->library(array('session','template','form_validation');
    }
}

/* My another function for form_validation and etc */

public function login(){
    $this->set_login_rules();
    if($this->form_validation->run()){
        /* inserting data to database */
        $this->session->set_flashdata('welcome');
        redirect('home/welcome');
    }
    $this->template->display('home');
}

public function welcome(){
    if($this->session->flashdata('welcome') !== FALSE){
        echo "<script>alert('Flashdata Success! Welcome!</script>";
    }
    else{
        echo "<script>alert('Flashdata Failed! Go Away!');</script>";
    }
}