\Header{CO2}{Carbon Dioxide uptake in grass plants}
\keyword{datasets}{CO2}
\keyword{nonlinear}{CO2}
\begin{Description}\relax
The \code{CO2} data frame has 84 rows and 5 columns of data from an
experiment on the cold tolerance of the grass species
\emph{Echinochloa crus-galli}.\end{Description}
\begin{Usage}
\begin{verbatim}data(CO2)\end{verbatim}
\end{Usage}
\begin{Format}\relax
This data frame contains the following columns:
\describe{
\item[Plant] an ordered factor with levels
\code{Qn1} < \code{Qn2} < \code{Qn3} < \dots{} < \code{Mc1}
giving a unique identifier for each plant.

\item[Type] a factor with levels
\code{Quebec} 
\code{Mississippi}
giving the origin of the plant

\item[Treatment] a factor with levels
\code{nonchilled} 
\code{chilled}

\item[conc] a numeric vector of ambient carbon dioxide concentrations (mL/L).

\item[uptake] a numeric vector of carbon dioxide uptake rates
(\eqn{\mu\mbox{mol}/m^2}{umol/m^2} sec).

}\end{Format}
\begin{Details}\relax
The \eqn{CO_2}{CO2} uptake of six plants from Quebec and six plants
from Mississippi was measured at several levels of ambient
\eqn{CO_2}{CO2} concentration.  Half the plants of each type were
chilled overnight before the experiment was conducted.\end{Details}
\begin{Source}\relax
Potvin, C., Lechowicz, M. J. and Tardif, S. (1990)
``The statistical analysis of ecophysiological response curves
obtained from experiments involving repeated measures'', \emph{Ecology},
\bold{71}, 1389--1400.

Pinheiro, J. C. and Bates, D. M. (2000) \emph{Mixed-effects Models in
S and S-PLUS}, Springer.\end{Source}
\begin{Examples}
\begin{ExampleCode}
data(CO2)
coplot(uptake ~ conc | Plant, data = CO2, show = FALSE, type = "b")
## fit the data for the first plant
fm1 <- nls(uptake ~ SSasymp(conc, Asym, lrc, c0),
   data = CO2, subset = Plant == 'Qn1')
summary(fm1)
## fit each plant separately
fmlist <- list()
for (pp in levels(CO2$Plant)) {
  fmlist[[pp]] <- nls(uptake ~ SSasymp(conc, Asym, lrc, c0),
      data = CO2, subset = Plant == pp)
}
## check the coefficients by plant
sapply(fmlist, coef)
\end{ExampleCode}
\end{Examples}

