“Iceberg lettuce” for purposes of this chapter means varieties of lettuce produced in California of the types which are distinguished as “crisphead” in that certain publication entitled “Lettuce Production in the United States, Agricultural Handbook No. 221,” August 1974 revision, issued by the Agricultural Research Service of the United States Department of Agriculture. The term does not include the types of lettuce otherwise distinguished in such publication by the terms “butterhead,” “cos or romaine” and “looseleaf.”