Endomycorrhizae has the added benefit of an extremely effective internal exchange mechanism (strengthens the mycelial network from the inside) as well as extending to the exterior of the root. In comparison, ectomycorrhizae exists only outside the root. Another deciding factor in which mycorrhizal fungi you should use is compatiblity: Endo bonds strongly with almost all leafy, green plants, whereas ecto form particularly well with confiers and oaks. *REMEMBER: Fruits, vegetables, flowers and most commercially produced plants love to ENDO, not ecto.*