Rediske, J. H., and K. R. Shea. (Weyerhaeuser Co., Forestry Research Center, Centralia, Wash.)The production and translocation of photosynthate in dwarfmistletoe and lodgepole pine.Amer. Jour. Bot. 48(6): 447–452. Illus. 1961.—A study was made, using C14O2, of the host‐parasite relationship of dwarfmistletoe (Arceuthobium americanumNutt.) growing on lodgepole pine (Pinus contortaDougl.) seedlings. The translocation patterns of radioactive photosynthate were outlined to determine the feasibility of using a systemic selective herbicide for dwarfmistletoe control. Selective administration of the C14O2for 24‐hr experimental periods in a controlled‐environment chamber demonstrated that dwarfmistletoe carried on photosynthesis and that a significant portion of the photosynthate (largely sucrose) was translocated into the pine. Photosynthate produced in a terminal needle cluster of the pine was translocated basipetally to the roots, but also was accumulated in intercepting dwarfmistletoe plants. Both glucose and fructose as well as sucrose were found in large amounts in pine‐produced photosynthate, but primarily sucrose was translocated, as demonstrated by paper chromatography. The principal damaging effect of the dwarfmistletoe appeared to be the cutting off of photosynthate translocation to the roots. The dwarfmistletoe acts as a biological girdle resulting in an accumulation of photosynthate above the site of infection. Presumably carbohydrates can be withheld from the roots in quantities sufficient to cause the characteristic decline of the tree that is associated with severe attack by dwarfmistletoe.