This collection consists of materials relating to Shull's work commissioned by the Carnegie Institution of Washington to collaborate with their grantee, Luther Burbank, with the aim of analyzing Burbank's data on plant breeding and hybridization and preparing it for publication in suitable scientific journals. Shull visited Burbank's plant-breeding farm in California eight times between 1906 and 1910. There are files for each plant genus involved in Burbank's work. These files contain notes, calculations, clippings from newspapers or periodicals, and an unpublished manuscript of Shull's final report to the Carnegie Institution. There is also a report by Edwin C. MacDowell, which gives background information about the collection.