From the Streets of Washington blog. Full article with many illustrations is at: http://www.streetsofwashington.com/2021/02/on-mall-agriculture-departments.html
The Department of Agriculture is the only federal agency with offices located directly on the National Mall. Agriculture's early presence on the Mall was no accident; it reflected the central importance of agriculture in 19th century America. Before the Civil War, most Americans were farmers, and after the war the advancement of scientific techniques for creating ever more diverse and productive farmlands was one of the country's central aspirations. Late 19th century tourists to Washington regularly visited the elegant red-brick Agriculture Department building, exploring its museum, marveling at its greenhouses and gardens on the Mall, and coming away reassured of America's scientific and economic pre-eminence.
The department's origins were within the Patent Office, one of the country's oldest government agencies and the one most closely associated with scientific advancement. In the 1830s, commissioner Henry Ellsworth devoted space at the Patent Office to preserving rare specimens of seeds and plants collected by American diplomatic missions abroad, and in 1839 a formal agricultural division was created. In 1862, President Abraham Lincoln signed the law establishing the Department of Agriculture as an independent agency "to acquire and diffuse among the people of the United States useful information on subjects connected with agriculture...and to procure, propagate, and distribute among the people new and valuable seeds and plants." The new department's first offices were a basement suite in the Patent Office building on F Street NW.
- John DeFerrari