If you have never heard of slime mold, or don't believe that it exists, then I have news for you. I've seen it with my own eyes, and it's in my backyard rose bed right now. The combination of moss and liverworts covering the rose bed is gradually maturing and slowly producing decayed material that is proving to be a good host for the mold. According to Wikipedia, there are more than 900 species of slime mold, and a search through Google Images shows that it comes in several different colors. Mine happens to be bright white, and the larger of the two lumps shown in the photos below measures around 1" by ¾". As you can see, it's just a few inches away from one of my roses, so I'll have to keep an eye on it.