The protoplasmic-streaming theory of phloem transport has been extended to include a transcellular streaming concept. Phloem exudate, concentration gradients, and the respiratory energy requirement are interpreted in terms of this concept. Physiological and cytological experiments are considered, and it appears that none of the unequivocal results contradict the proposed model. Reconciliation of apparently conflicting evidence is possible because transcellular streaming is primarily a fluid flow phenomenon and is directly dependent on respiration for its motive force energy. As in other theories, it is difficult to understand how the measured rates of mass transfer occur through the phloem. The present model may be able to meet quantitative demands because of increased efficiency due to the direct linear pathways provided by transcellular strands, and the increased cross-section of sieve-tube cytoplasm. More facts are required before the mass transfer problem can be resolved.