Fig. 1

Vessel and fiber cell characteristics of TW, OW and NW. Tension wood (a, d and j). Opposite wood (b, e and k). Normal wood (c, f and l). Vessel (v). Ray parenchyma (rp). Cell corner (CC). Secondary cell wall (S). Cell middle lamella (CML). Second secondary cell wall (S2). ** indicates significant differences at a significance level of 5%