Spruce  R Documentation 
Growth of Spruce Trees
Description
The Spruce
data frame has 1027 rows and 4 columns.
Format
This data frame contains the following columns:
 Tree

a factor giving a unique identifier for each tree.
 days

a numeric vector giving the number of days since the beginning of the experiment.
 logSize

a numeric vector giving the logarithm of an estimate of the volume of the tree trunk.
 plot

a factor identifying the plot in which the tree was grown.
Details
Diggle, Liang, and Zeger (1994, Example 1.3, page 5) describe data on the growth of spruce trees that have been exposed to an ozonerich atmosphere or to a normal atmosphere.
Source
Pinheiro, J. C. and Bates, D. M. (2000), MixedEffects Models in S and SPLUS, Springer, New York. (Appendix A.28)
Diggle, Peter J., Liang, KungYee and Zeger, Scott L. (1994), Analysis of longitudinal data, Oxford University Press, Oxford.