"From another American species, dear, which is very much like the white elm that we have been considering. The slippery elm is a smaller tree, does not droop so much, and the trunk is smoother and darker. The leaves are thicker and very rough on the upper side. The inner bark contains a great deal of mucilage--that, I suppose, is the reason for its being called 'slippery'--and it has been extensively used as a medicine. The wood is very strong and preferred to that of the white elm for building-purposes, although the latter is considered the best native wood for hubs of wheels. There is a great elm tree on Boston Common which is over two hundred years old, and another in Cambridge called the 'Washington Elm,' because near it or beneath its shade General Washington is said to have first drawn his sword on taking command of the American army. In 1744 the celebrated George Whitefield preached beneath this tree."