Agronomy and Horticulture Department


Date of this Version



Published in Physiological Aspects of Crop Yield: Proceedings of a symposium sponsored by the University of Nebraska, the American Society of Agronomy, and the Crop Science Society of America, and held at the University of Nebraska, Lincoln, Nebr., January 20-24, 1969. Edited by Jerry D. Eastin, F. A. Haskins, C. Y. Sullivan, C. H. M. Van Bavel, and Richard C. Dinauer (Madison, Wisconsin: American Society of Agronomy & Crop Science Society of America, 1969). Copyright © 1969 American Society of Agronomy & Crop Science Society of America. Used by permission.


The mechanism of translocation has been discussed since the latter part of the 19th Century, when DeVries, in 1885, proposed protoplasmic streaming as the mechanism. Since that time O. F. Curtis, beginning about 1920, and more recently Thaine (1961) and Canny and Phillips (1963) have become interested in this approach to the problem. In the meantime Munch, in 1930, proposed a pressure flow mechanism based on a turgor pressure gradient in the phloem between metabolite supplying and metabolite consuming areas. These two mechanisms, and others, are fully discussed in Swanson (1959), so the present paper will deal with a compilation of the factors upon which a sound view of mechanisms must rest. It does not seem possible to arrive at a decision as to mechanisms on the basis of any narrow approach to the subject. The distribution system itself is complex in its cellular make-up, ramifies to all parts of the plant body, and lacks a centralized pumping mechanism. For these reasons it is considered, by most workers in the area, that a very broad knowledge of the plant and its processes is necessary if one is to evaluate the phenomenon of translocation fruitfully.