Fig. 1.

Secondary cell wall development is correlated with stem maturation. a A representative stem of 7-week old M. truncatula plants. Medicago plants normally have ten to eleven internodes at this stage. b to f Stem cross sections observed under UV light. The blue color is autofluorescence from lignified secondary cell walls. From the plant apex to the bottom, the internodes become more mature and the stems accumulate more secondary cell walls