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

Data originally from Hunt, R. (1973).  ``A method for estimating root
efficiency.'' {\em Journal of Applied Ecology\/}~{\em 10}, 157--164.

These are the log phosphorus contents (ln micro gram/plan) of 8
plants.  The first 4 responses) are after 15 days, and the last
four after 28 days.