A data set from Oehlert (2000) \emph{A First Course in Design and
Analysis of Experiments}, New York: W. H. Freeman.

Data originally from Table 17 of M. Sutheerawattananonda (1994)
"Variation in Physical Properties and Microstructure of
Extruded Wheat Flours", MS Thesis, University of Minnesota.

These data are the size of the air cells in the "expanded
extrudates" of flours.  Column 1 is size in mm^2.  Column 2
is the variety of wheat (cultivar) used to make the flour.
Column 3 is the location where the wheat was grown.  Column 4
is the temperature at which the extrusion was performed
1=120C, 2=180C.