The effectiveness of oxygen movement through pea seedlings has been assessed firstly by assaying for radial oxygen loss along the roots using the cylindrical Pt electrode technique, and secondly by measuring root growth in various oxygen-free media.
It was found that roots would grow in oxygen-free 3% agar to a length exceeding 20 cm, but when such plants were removed to oxygen-free 0.05% agar oxygen could not be detected in the apical segments in roots longer than 9.5 cm unless respiratory activity was curtailed by cooling.
If the greater part of the root was retained in 3% agar and only the apical region exposed to 0.05% agar and assayed, oxygen loss always occurred. It was concluded that the 3% agar has a jacketing effect substantially reducing oxygen leakage from the root surface and thus allowing more oxygen to channel down to the apical regions.
Root growth in unstirred air-saturated 0.05% agar matched the growth in oxygen-free 3% agar. Root growth in unstirred oxygen-free 0.05% agar was arrested at c. 9 cm.
It is suggested that the effect produced by the aerated unstirred 0.05% agar is consistent with a jacketing effect mitigating oxygen loss from the root and that a growth of 9 cm in unstirred deoxygenated agar is consistent with a smaller jacketing effect due to the unstirred medium.
It is proposed that the accumulation of respiratory tissue will eventually render inadequate any jacketing effect. Further aerobic development at this stage will require a supply of oxygen from the rooting medium.