Currently the most advanced model for how growth stresses develop within the cell wall was presented by \citet{Alm_ras_2005} using the unified hypothesis \citep{okuyama1986,Okuyama_1994,yamamoto1991,ISI:A1992HP18200001,Yamamoto_1998} utilising both the lignin swelling and cellulose contraction hypotheses. For details see Section \ref{section:GS}.