Histochemistry of stem transversal sections from controls and single or double transformants. Staining with Wiesner (A) or Mäule (B) reagent was carried out on sections of control plants (a and g), B10 (ASCOMT I, b and h), B31 (ASCCR, c and i), and B68 (ASCCR, d and j) single transformants, or double transformants issued from B31 × B10 cross (e and k) or B68 × B10 cross (f and l).