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Transversal sections of needles from maritime pine plants derived from somatic embryos matured at 18 °C (a), 23 °C (b), or 28 °C (c) before (a, b, and c, respectively) or after (d, e and f, respectively) a heat treatment for 10 days at 45 °C for 3 h/day. Note epidermis and chlorenchymatic tissues. Bar, 50 µm.
