Distribution of Tulip and Narcissus Bulbs in 1919, USDA Circular 65
The Production of Narcissus Bulbs, David Griffiths, 1924, USDA Bulletin 1270
Daffodils, David Griffiths, USDA Circular 122, October 1930, revised March 1934
Bulbs from Seed, David Griffiths, USDA Circular 311, June 1934
Narcissus Bulb Fly, USDA, 1977