Chocolate Tube slime moldStemonitis splendens
I had heard of slime molds (Myxomycetes), but I didn't know much about them until I attended a workshop about myxomycetes at the Great Smoky Mountains Institute at Tremont in July 2004. These organisms are in the Kingdom Protista and are often invisible until they enter their vegetative (reproductive) phase, where they produce brightly colored spores. Slime molds begin their life cycle as a multi-nucleated spore which becomes an amoeba. This large cell reproduces and becomes a slowly-moving organism called a "plasmodium." The plasmodium oozes across dead leaves and decomposing fallen logs in search of bacteria to consume. When the plasmodium has had enough to eat it produces a spore case, which can be quite colorful.
This species is large and fairly easy to find, it is my "favorite" slime mold (strange as that may sound!). The spore stalks are up to 1/4" tall. I found this growing on a decaying log at the University of Tennessee Arboretum in July.