Brooks's reflections on botany in Sapporo and on his teaching tenure at Sapporo Agricultural School can be found in his letters to his sister Rebecca. These letters frequently refer to Rebecca's failing health and in them William Brooks offers advice to his sister regarding her well-being. It remains unclear what was the cause of Rebecca's poor health, but there are mentions of digestive problems and the need for good nourishment and fresh air. Another topic documented in these letters is the description of life in Japan, including such details as the noise made by frogs, which were numerous in Sapporo, the construction of houses, and the organization of Japanese households. According to Brooks, the Japanese took down the walls of their houses during the day so that the inner arrangement of their houses was displayed. One letter refers to kite flying as a national past time and another letter describes Japanese theater as always based on an historical narrative. Brooks is attentive to plant life and the different kinds of food which are available in Sapporo.

In the letters of Eva Brooks to William's sisters Rebecca and Martha, she writes of her domestic duties such as milking the cow, making butter, and a taking trip to various cities of Japan with her daughter Rachel. She itemizes the objects that she bought on this trip in order to bring them back to Massachusetts upon the completion of William's tenure at Sapporo Agricultural School.

Contains an account book, probably kept by Eva Brooks, dated 1896 to 1923, with pages 16-25 and 46-49 removed. Other materials in this series are newspaper clippings, translations, the biographical sketches of Brooks and the Baron Shosuke Sato, a map of Hokkaido University, a Japanese poem translated into English by Brooks's students, and a salary receipt for Brooks's work at the Experiment Station.

The photographs consist of portraits of staff and graduating students from three classes at Sapporo Agricultural College as well as scenes of Japan and Massachusetts.