The cabbages data set has 60 observations and 4 variables
cabbagesThis data frame contains the following columns:
CultFactor giving the cultivar of the cabbage, two levels: c39
      and c52.
DateFactor specifying one of three planting dates: d16,
      d20 or d21.
HeadWtWeight of the cabbage head, presumably in kg.
VitCAscorbic acid content, in undefined units.
Venables, W. N. and Ripley, B. D. (2002) Modern Applied Statistics with S-PLUS. Fourth Edition. Springer.