This collection contains seven letters to Smith about the identification of plants, particularly relating to Lobeliaceae, Agave Linnaeus and Annonaceae, from Ignatius Urban (1848–1931), Benjamin Lincoln Robinson (1864–1935), Charles Baron Clarke (1832–1906), Casimir de Candolle (1836–1918), William Trelease (1857–1945) and William Edwin Safford (1859–1926). There is also a commentary, which originally may have been included with the Candolle letter, from Robert Buser (1857–1931) about Lobelia tuerckheimii Rendle and L. parviflora M. Martens & Galeotti.