Y l = µ + T + ε l ,
where Y l = {Y 1l , Y 2l } are
the observed measurements on a stem at
the two
growth periods, µ = { µ 1 , µ 2 } are
the corresponding population
mean values for
the two dates and T is treatment vector. ε l ∼ N(0, cov( ε l , ε ´ l )) m[r]