Silent Running depends on the excellent special effects of debuting director Douglas Trumbull and his team and on the appreciation of a literate but broadly entertaining script. Those being the highlights, they are virtually wiped out by the crucial miscasting of Bruce Dern. As a result, the production lacks much dramatic credibility and often teeters on the edge of the ludicrous.Dern and three clod companions man a space vehicle in a fleet of airships containing vegetation in case the earth again can support that type of life. But the program is scuttled, all hands are recalled, but Dern decides to mutiny. In the process, he kills his three shipmates and goes deeper into space. His only companions are two small robots, whose life-like qualities are rather touching.