List of sources:
Cape of Good Hope almanac and annual register, 1858, 1859. Cape Town: Van de Sandt de Villiers.
Cape of Good Hope. Report of the Meteorological Commission, 1893.
Eastern Province Naturalists' Society. Ninth annual report, for the year 1890. Port Elizabeth: James Kemsley, 1891.
Eastern Province Naturalists' Society. Minute book [No. 1], January 1882 - May 1885; Minute book [No. 2], July 1885 - March 1892. (Port Elizabeth Public Library).
Eastern Province year book and annual register, 1862. Grahamstown: Godlonton & Richards.
FamilySearch: Russell Hallack. https://ancestors.familysearch.org/en/G6P5-T28/russel-hallack-1824-1903 AND https://www.familysearch.org/ark:/61903/3:1:3Q9M-CSQ8-WDRK?view=index&personArk=/ark:/61903/1:1:QG5G-LKM5&action=view&cc=2517051
General directory of South Africa, 1890/1, 1903.
Grahamstown Journal, 14 July 1882, p. 3: Port Elizabeth Naturalists' Society.
Gunn, M. & Codd, L.E. Botanical exploration of southern Africa. Cape Town: Balkema, 1981.
Harvey, W.H. & Sonder, O.W. Flora Capensis, being a systematic description of the plants of the Cape Colony, Caffraria, and Port Natal (Vol. 1). Ashford, Kent: L. Reeve, 1894 (originally published 1860).
South African Magazine, 1867, Vol. 1, pp. 198-199: Port Elizabeth Natural History Society.