Subseries 30a contains correspondence of the Agricultural Experiment Station and the Florida Cooperative Extension Service, written during the period that Peter Henry Rolfs directed both, with bureaus of the United States Department of Agriculture. (The subseries also contains a few files of correspondence with other federal agencies on matters related to wartime agricultural issues and land fraud schemes.) The principal USDA bureaus represented here are Animal Industry, Plant Industry, and the States Relation Service. The files include substantive letters and telegrams of the Station's and Service's director and the various department heads on issues of state and regional concern, but also contains trivial communication on administrative and insignificant matters from other staff members. There are no subject divisions and little attempt has been made to remove unimportant documents.

A large portion of the subseries consists of correspondence with the States Relation Service. The files titled "Office of Extension Work in the South" document the early development of the Florida Cooperative Extension Service and reveal many agricultural and rural issues germane to the southern states.

Correspondence is arranged by name of agency and then chronologically.

Subseries 30b contains the correspondence of the Agricultural Experiment Station and the Florida Cooperative Extension Service with agencies of the federal government, primarily the United States Department of Agriculture. (The sole exception is a single folder of correspondence with the War Production Board.) The principal USDA bureaus represented here are Agricultural Economics, Animal Industry, Entomology and Plant Quarantine, and Plant Industry. Also included are the Office of the Secretary of Agriculture, Office of Experiment Stations, Office of Cooperative Extension, the Soil Conservation Service, and the States Relation Service.

The correspondence with the Bureau of Animal Industry documents cattle and sheep experiments. Of regional interest are the records related to the development of the Chinsegut Hill Sanctuary in the 1930s. The files of the Bureau of Entomology and Plant Quarantine provide a detailed history of local and regional insect infestations, particularly for the 1930s. The Bureau of Plant Industry documents the introduction of new plants into the state and work with existing plant industries. Some correspondence concerning the identification of native plants was also retained. From 1921 through 1927, the Plant Industry correspondence was filed in a single miscellaneous file. After 1927, the correspondence is arranged by the names of particular individuals at the Bureau. Only the files of those individuals involved in substantive matters were retained. However, no attempt was made to remove routine administrative correspondence and other trivia from the earlier files.

Correspondence is arranged by name of agency.