1. The Ecospecies-Prelude to Discussion
2. Reproductive Methods as Factors in Speciation in Flowering Plants
3. G. Bentham (1874). Rep. Brit. Soc. Advanc. Sci. for 1874, 27.
4. A. F. Blakeslee, A. D. Bergner and A. G. Avery (1937). Cytologia (Fujii Jub. Vol.), 1070.