"Most of the plants in every part of the world, sir, are di-cotyledons. They all have net-veined leaves; but some of them are herbaceous, and die down to the ground every season. These, of course, have no woody stem. The nature of the woody stem of the di-cotyledon can be easily understood from a piece of the stem or branch of one of our common trees. This always has a central pith, with the hard solid wood arranged round it in layers or circles.
