This collection consists mainly of letters Prain received from 1922 to 1924 and miscellaneous related items, some concerning the 1922 death of Isaac Bayley Balfour (1853–1922). Also found here is a copy of a letter (27 February 1922) from Prain to Nathaniel Lord Britton (1859–1934), discussing the nomenclature of various plants. Among the correspondents are Agnes (Balloch) Bayley Balfour (1857–1940), Frederick O. Bower (1855–1948) and Arthur W. Hill (1875–1941).