Studies on the Transport of Oxygen Through the Stems and Roots of Vegetable Seedlings

S ummary Experiments were carried out to determine whether oxygen could enter the leaves of vegetable seedlings and be transported through the tissues to the roots. The technique involved embedding seedlings in agar/potassium phosphate gel to exclude oxygen; the atmosphere around the leaves was varied and oxygen concentrations were measured at points on the root surface 0.5–2.0 cm from the junction of stem and root system. When the gas around the leaves was changed from nitrogen to oxygen, the oxygen concentration at the root surfaces increased rapidly. The rates of increase agreed approximately with those calculated by assuming that the plants contained continuous non‐tortuous gas‐filled channels, the view that diffusion through these channels was the means by which oxygen was transported through the plant, and that the gas channels were within about 12 μ of the root surfaces. Experiments were also carried out to determine whether the roots of seedlings could grow in oxygen‐free media. Seedlings were grown in an atmosphere of air with their roots in columns of agar‐gel containing yeast and glucose. Depending on the amount of yeast and glucose in the gel, the oxygen concentration fell to zero at depths of between 0.5 and 2.0 cm from the gel surface. Seedling roots rapidly penetrated oxygen‐free zones in the gel but the extent of penetration appeared to be unrelated to the depth of zero oxygen concentration. A similar pattern of results was obtained with seedlings of twelve different species and it was concluded that the stems and roots of most seedlings contain continuous, non‐tortuous gas channels through which oxygen diffused. When the plants were grown under anaerobic conditions such diffusion could satisfy all the roots’requirements for oxygen.