The ponytail palm takes its name from its resemblance to hair cascadeing out of a ponytail. It's also called a "bottle palm" because its trunk becomes a bottle like bulb at soil level. Because of its massive size the plants are mostly root-bound. While they can store water in their bulb, and use their water slowly, they probably don't have a lot of soil in their pot. If the roots become too dry the lower leaves turn brown or yellow and the plant looks a little ashy.