We've already seen Dell embracing the bamboo woods to package its products, so what's next for Round Rock's green fingers? Mushrooms, apparently. Unveiled at the Fortune Brainstorm Green conference yesterday is a biodegradable cushioning tray, which is grown -- yes, grown -- out of a mold stuffed with old cotton hulls, mushroom spawn, and nutritious agricultural waste. While it does take about five to ten days for the mycelium (aka mushroom root) to form the desired shape, the merit of such process is that all the energy required for the manufacture is provided by