This series concerns mostly incoming correspondence. The letters include professional correspondence regarding botanical research, specifically focusing on the Bidens family of plants, and from a variety of authors, many of which are letters thanking Degener for copies of his Flora Hawaiiensis and samples of flora. They also discuss his concern for the rare plants of Hawaii in general and the government of Hawaii. Several other topics are covered as well. Included are two notebooks written in by Ray Toppings, and a reunion booklet from Massachusetts Agricultural College (today the University of Massachusetts-Amherst) which contains a biographical sketch of Degener.