WebCamTexture not working on Instance objects

Hi, I'm trying to give WebCamTexture to some Boxes (Instantiated) it works on Simple Cubes but when I Instantiate those Cubes It shows them All Black .

Here's the Webcam Function :

 void Start() {
     WebCamTexture webcamTexture = new WebCamTexture();
     renderer.material.mainTexture = webcamTexture;
     webcamTexture.Play();
 }