format
A data frame with 511 records and 5 variables: Plant, identifier of the apple tree, 1-8;Stock, root stokcing, one of three different root stocks: Mark, MM106 and M26 ; Spacing, between-row $\times$ within-row spacings, one of the following two: $4 \times 2$ meters and $5 \times 3$ meters; Zone, inner or outer; RLD, root length density.source
de Silva, H. N., Hall, A. J., Tustin, D. S. and Gandar, P. W. (1999). Analysis of distribution
of root length density of apple trees on different dwarfing rootstocks. Annals of
Botany, 83: 335-345.Dunn, P.K. and Smyth, G.K. (2005). Series evaluation of Tweedie exponential dispersionmodels densities. Statistics and Computing, 15, 267-280.