The data we are viewing is the cabbages dataset from the MASS package. It contains 60 observations of 4 variables.

• Cult Factor giving the cultivar of the cabbage, two levels: c39 and c52.
• Date Factor specifying one of three planting dates: d16, d20 or d21.
• HeadWt Weight of the cabbage head, presumably in kg.
• VitC Ascorbic acid content, in undefined units.

Rawlings, J. O. (1988) Applied Regression Analysis: A Research Tool. Wadsworth and Brooks/Cole. Example 8.4, page 219. (Rawlings cites the original source as the files of the late Dr Gertrude M Cox.)