PHP - init parent varialbles (with constructor)

I am newbie with php! I have task to create class(Request) that have constructor which have one parameter ($_SERVER) and another class (GetRequest) who extends Request. My code is:

<?php

class Request{
    protected $server;

    public function __contruct($ser){
        $this->server = $ser;
    }

    public function getMethod(){
        return $this->server['REQUEST_METHOD'];
    }

    public function getPath(){
        return $this->server["PHP_SELF"];
    }

    public function getURL(){
        return 'http://'.$this->server['HTTP_HOST'].$this->server['REQUEST_URI']; 
    }

    public function getUserAgent(){
        return $this->server['HTTP_USER_AGENT'];
    }
}

class GetRequest extends Request{

    function __contruct($ser){
        parent::__construct($ser);
    }

    //Return query string params in JSON format
    function getData(){
        $keywords = preg_split("/[\s,=,&]+/", $this->server['QUERY_STRING']);
        $arr=array();
        for($i=0;$i<sizeof($keywords);$i++) {
            $i++;
            if (!isset($keywords[$i])) {
                $keywords[$i] = null;
            }
            $arr[$keywords[$i]] = $keywords[$i];
        }
        $obj =(object)$arr;
        return json_encode($obj);
    }
}

echo $_SERVER['REQUEST_METHOD'].'<br/>';
if ($_SERVER['REQUEST_METHOD'] === 'GET') {
    $getReq = new GetRequest($_SERVER);

    echo $getReq->getMethod().'<br/>';
    echo $getReq->getPath().'<br/>';
    echo $getReq->getURL().'<br/>';
    echo $getReq->getUserAgent().'<br/>';
    echo $getReq->getData().'<br/>';
}

?>

But the output with http://localhost/HW1/Task3/61807_new.php?http://localhost/HW1/Task3/61807_new.php?a=1&b=2 is following:

GET

http://

{"":null}

Expected output is:

GET

GET

/HW1/Task3/61807_new.php

http://localhost/HW1/Task3/61807_new.php?a=1&b=2

Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/56.0.2924.87 Safari/537.36

{"a":"1","b":"2"}

I can't see where is problem! It looks like $server is not initialize but i don't now why!