A roomer is someone that rents out a room. Roomer sounds like the word "rumor". A rumor is a circulating story of uncertain truth that is spread by word of mouth. This joke is playing on the word "roomer" because it sounds like "rumor" and the person being referred to is a landlady, which is someone that rents out spaces to other people.
When gossip finally led to the landlady ' s arrest for murdering her tenants and scattering parts of their bodies around town , her only comment was , ' ' Well , that ' s what comes of spreading roomers . ' '