Sounds like the flap track fairings to me as well.
So to answer your question: they are flap track fairings. The flaps have mechanisms for extension, typically in the form of jackscrews. In order to reduce drag and decrease exposure to the elements, the mechanisms (flap tracks) are enclosed in fairings. If a fairing is missing or damaged, most aircraft can dispatch without it but there is a fuel burn penalty.
As Blackbird says, they are often called canoes or canoe fairings.
Another "growth" (I love that) is the drag reducing bump on the underside of 340 wings. IIRC it is close to the outboard engine. I'm sure someone can dig up a pic.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo