The Norfolk Island pine grows so slowly--3 to 6 inches a year under living-room conditions--that no indoor gardener has to be concerned about cutting a hole through to the attic to accommodate its mature height. Nevertheless, a 15-year-old specimen makes a handsome indoor "tree" 4 to 6 feet tall, with rich, silky dark greer needles and gracefully drooping branches that give it a distinctive Oriental look.