The drawing sheets include visual matter associated with the patent, generally black and white drawings provided by the applicant in India ink. The USPTO has precise requirements for formatting, sizing, and other details for applicants. One important guideline to keep in mind while searching and reading patent documents is that the drawings must depict all features specified in the claims section.
In the case of the oat plant patent example, the drawing depicts the pedigree and chronology of crosses for the plant.