Well, a genre is a type of literary work.  The novel, the short story, and the play (for example) are all literary genres.  Each genre has its own set of characteristics, which are often referrred to as "conventions." Some genres have "subgenres" as well.  The "detective story," or "historical fictin" for example, are "subgenres" of the novel. "Chrysanthemums" is a short story, and as such adheres to its conventions, such as a length of about 15,000 words (not all short stories conform to this,of course), having just a few characters (1 main characters in Chrysanthemums), focusing on a single incident (her encounter with the tinker man), and a single setting. The short story also has a unity of effect, tone, mood, and impression. Typically a short story reveals character (the wife), usually by means of a single central and representative incident (as opposed to developing a character over a long period of time). Chrysanthemums might be said to belong to the subgenre of "realistic short story" (as opposed to fantasy).