This collection consists of correspondence with three individuals. Handwritten correspondence from Thomas Baillie MacDougall (1895–1973) to Carlson and her life partner, Kate Staley, is dated 1949 to 1967. Most of these letters are one to two pages in length and were sent from New York, New York, or Tehuantepec, Oaxaca, Mexico. This set of letters includes 34 letters and five postcards, sometimes signed “D. Tomás,” and one 3" × 5" printed paper advertising the Hotel Tehuantepec (Mexico). The second set has four letters, all in Spanish, of correspondence with Faustino Antonio Miranda González (1905–1964) of the Instituto Botanico del Estado, Mexico, dated 1952 to 1956. Finally, the collection includes three letters to Carlson from Judith S. Stix (also Mrs. Ernest W. Stix) of St. Louis, Missouri, concerning MacDougall’s work.