The trail from plan breeder to farmer-from 5 pounds of seed to thousands of bushels- is a long and tedious one. Mixtures from other crops or other varieties by mechanical means or human carelessness must be controlled all the way.
Geiser, D. S.
"How Crops Are Kept Pure,"
Iowa Farm Science: Vol. 6
, Article 2.
Available at: https://lib.dr.iastate.edu/farmscience/vol6/iss4/2