In late 1872 Charles Sprague Sargent was appointed director of the Botanic Garden, the newly constructed Arnold Arboretum, and new botany-related buildings. This freed up much of Gray's time. Also, late in 1872, Ignatius Sargent, Charles' father, and Horatio Hollis Hunnewell both agreed to donate $500 yearly each to support Gray so that he could devote "undivided attention" to completing "Flora of North America". This is what finally allowed Gray to resign his professorship and devote all his time to research and writing.