We conduct interdisciplinary research on the cell biology and physiology of phloem transport. Integral to these projects are studies of leaf development, the structure and function of plasmodesmata, and virus movement. Molecular, physiological, and anatomical techniques are employed in approximately equal measure. Our primary interest is in phloem loading, the active accumulation of sugars in minor vein sieve elements and companion cells. Loading creates the pressure that drives long-distance flow and therefore motivates the distribution of organic nutrients and many protective compounds. One of our contributions to this area is the Ôpolymer trapÕ model that explains loading through plasmodesmata, long thought to be thermodynamically impossible. We have also found that the primary products of photosynthesis in certain plants (e.g. willow and apple) are not actively loaded at all, in the thermodynamic sense. Rather they diffuse from mesophyll cells into the phloem. This may prove to be a common transport mechanism, since plants with symplastically connected minor vein phloem constitute almost half of all dicotyledonous species.