Walters, Chris; Towill, Leigh (2004). "Seeds and Pollen"(PDF). Agricultural Handbook Number 66 The Commercial Storage of Fruits, Vegetables, and Florist and Nursery Stocks. USDA-ARS, National Center for Genetic Resources Preservation Preservation of Plant Germplasm Research, Fort Collins, CO. Archived from the original(PDF) on 2009-03-20. Retrieved 2008-06-21.
Walters, Chris; Towill, Leigh (2004). "Seeds and Pollen"(PDF). Agricultural Handbook Number 66 The Commercial Storage of Fruits, Vegetables, and Florist and Nursery Stocks. USDA-ARS, National Center for Genetic Resources Preservation Preservation of Plant Germplasm Research, Fort Collins, CO. Archived from the original(PDF) on 2009-03-20. Retrieved 2008-06-21.