Hugo De Vries
TWIN HYBRIDS OF OENOTHERA HOOKERI T. AND G
Genetics 1918 3: 397–421
[PDF]  

Hermann J. Muller
GENETIC VARIABILITY, TWIN HYBRIDS AND CONSTANT HYBRIDS, IN A CASE OF BALANCED LETHAL FACTORS
Genetics 1918 3: 422–499
[PDF]