Figure 5.

Surface oxygen concentration of roots at various distances from the root apex embedded in stagnant and oxygen-free agar. Measurements on T. juruana and S. martiana were performed on 10- to 12-d-old adventitious roots. In the cases of L. corymbulosa and C. benthami, where cultivation in anoxic agar did not induce adventitious roots, pre-existing roots were used for the determinations. ROL was only observed in roots of T. juruana and S. martiana. Adventitious roots of T. juruana exhibited oxygen leakage to the rhizosphere only in a small (approximately 5 mm wide) zone at the root tip. No outward diffusion of oxygen was detectable from roots of L. corymbulosa and C. benthami. Lengths of the roots were 12 cm (S. martiana), 5 cm (T. juruana), or 6 cm (L. corymbulosa and C. benthami). Determinations were performed on 20 different roots from at least six individual plants without major deviations in the overall pattern. Data are from a representative experiment.