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

Data originally from Richards, J.~A. (1965).  ``Effects of fertilizers
and management on three promising tropical grasses in {J}amaica.''
{\em Expl. Agric.\/}~{\em 1}, 281--288.

Columns are height, fertilizer, interval, and response (cwt/acre).
Codes 1, 2, 3 for height are 1, 3, 6 inches.
Codes 1, 2, 3, 4 for fert are 0, 8, 16, 32 cwt/acre.
Codes 1, 2, 3, 4 for interval are 1, 3, 6, 9 weeks.