Rodney True's professional correspondence is heavily stilted toward the years spent at the University of Pennsylvania, post-1920. Although there is comparatively little to document True's work as a plant physiologist, the letters offer insight into his historical research, particularly on Thomas Jefferson and the Bartrams, and his activities on behalf of the Philadelphia Society for Promoting Agriculture (P.S.P.A.) and the Pennsylvania Horticultural Society. In addition to the folders filed under the name of the organization, several individual correspondents were involved with the P.S.P.A., most notably George F. Curwen and John M. Okie.

There is some documentation of his activities as Director of the Morris Arboretum of the University of Pennsylvania and administrative correspondence relating to the Allegheny Forest Experiment Station run by the U.S.D.A.

True's correspondence with John Frazer represents the happy merger of his interests in botany and history. True and Frazer exchanged a number of letters in their efforts to determine the original site of discovery of the "Franklin Tree," Franklinia alatamaha (also called Gordonia alatamaha), but were also busy exchanging information of plant physiology. True's correspondence with I.I.R. Henry is focused on study of the Bartrams and Bartam's Garden.

An interesting series of letters relate to the "Darlington Gas Case," the Darlington Florists sued the local gas company over damage to its plants from a leaky gas main. True's plant forensic skills were called in to testify in a case that eventually made its way to the Pennsylvania Supreme Court before being decided in favor of the plaintiffs. A series of newspaper clippings related to the case are housed in Series V.

Other correspondence of note includes a series of letters from the botanist C.H. Arndt describing his work in Haiti in the 1920s, letters from George F. Mitchell on tea (True had an interest in promoting tea cultivation in America), and the letters of several correspondents relating to botany and natural history in Maine, where True summered (see, e.g., Frank Morgan Jones, William T. Hussey, Mary Carpenter Kelley, Anne E. Perkins).

Correspondence of various members of the families of Rodney H. True and his wife Katherine. Although the bulk is purely personal, True's research interests and personal interests often overlapped, and several correspondents mingle the professional and personal. His brother Gordon, an agricultural scientist at the University of California (Berkeley and later Davis), is particularly prone to discuss his academic endeavors and his efforts to better himself professionally, and True's sisters Eunice and Katherine, teachers at Berea College, also provide details on their academic careers.

The remaining correspondence provides a perspective on the social and family life of Rodney and Katherine True, including . The bulk of the correspondence falls in the period between 1910 and 1930.

Notebooks, memorandum books, and accounts kept by Rodney H. True. The series includes a valuable set of notes kept by True while studying for his doctorate at the University of Leipzig, including notes for comparative anatomy, general botany, general zoology, and paleontology.

Several later notebooks pertain to True's research in plant physiology and to his research on Thomas Jefferson. Series I includes three "logs" of botanical excursions 1930, 1931 and 1936. One volume includes fairly extensive genealogical notes of True's.

Miscellaneous diaries of Rodney H. True, kept sporadically. For the most part, the diaries written prior to 1917 include perfunctory daily notes on True's professional activities, with occasional personal comments, but the diaries for 1917-1919 include longer and more interesting passages. Although True was not a retrospective diarist, he commented regularly on the news from Europe and, to a lesser degree, on the home front, where he used his knowledge of agricultural science to assist in raising food for the war effort. The diaries for 1883 and 1926 are very brief, the latter being more an appointment book than a true diary.

A completely miscellaneous assemblage of printed materials, ranging from newspaper clippings to reprints, ephemera, and small publications by groups in which True had a professional or personal interest. These include a few pamphlets relating to the Pennsylvania Horticultural Society, the Philadelphia Society for Promoting Agriculture, and the University of Pennsylvania.