http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
with illustrated keys for their identification, together with a general account of their structure and economic importance
by E. Mead Wilcox, George K.K. Link, and Venus W. Pool.
Bulletin of the Agricultural Experiment Station of Nebraska ; no. 148