The electroosmotic theory of phloem transport: a final restatement

The electroosmotic theory as published in 1974 is subjected to a detailed re‐examination, mainly in connection with the problems of anion transport and of the sheer magnitude of the transmembrane potassium current it necessitates. The result is a fundamental modification of the theory which appears very promising. A proton excretion pump replaces the potassium pump; anion transport now presents little difficulty. A modification of the scheme is proposed to incorporate plants like Cucurbita whose P‐protein is basic. The new suggestions appear to offer themselves fairly readily to experimental test. Anion transport in the phloem appears to differ somewhat fundamentally from cation transport.