Plow and sunset

On Wednesday, we discussed a few interpretations of Cather's image of the plow silhouette in the setting sun. I indicated that I found it helpful to read the plow as a "bidirectional" emblem. What did you make of this concept of "bidirectionality"? What does that mean? And, I also want to give you an opportunity here to tell me what you think the plow silhouetted in the setting sun conveys, in regard to the novel's narrative, in regard to the settlement of the Plain, to technology, to our treatment of the environment, etc. I will look forward to reading your replies.