What does Elisa see at the end of "The Chrysanthemums" that makes her sad?

In John Steinbeck’s story, Elisa has greatly enjoyed discussing gardening with the itinerant peddler who has stopped by the farm. Although some part of her understands that she is trying to sell her things, she convinces herself that he shares her enthusiasm for the chrysanthemums that she loves growing and has been talking about with him. She gives him a few plants to take with him.
Their conversation brightens her spirits so much that she gets dressed up to go to dinner with her husband. While they are driving down the road, she sees her gift of chrysanthemums lying in the road. She does not say anything to her husband, who drives on past the “dark speck.” The experience saddens her, because she knows the peddler did not appreciate what she valued. At the end, she cries as if she were already old at thirty-five.