GUI Display

Hey everyone, I'm currently working on a game for a class I have and I need just a little bit of help.

This is what the code looks like...

 var Cactus : Texture2D;
 var Cactus2 : Texture2D;
 var button1clicked=false;
 
 function OnGUI () {
     if (GUI.Button (Rect (375, 100, 150, 100), Cactus)) {
         if(!button1clicked)
             button1clicked=true;
         else
             button1clicked=false;
     }
     
     if(button1clicked){
         GUI.Box(Rect(375, 210, 315, 300), "");
         GUI.Label(Rect(375, 210, 90, 90),"Cactus");
         GUI.Box(Rect(10, 370, 350, 140), Cactus2);
     }    
 }

What I want to happen is when I click another button, the previous button is deactivated.

Does anyone know what the code would look like? All the help would be greatly appreciated! :D