A lenticel is formed by the phellogen at a given spot dividing very actively and giving rise to a loose tissue of rounded cells which soon lose their contents, and between which air can pass to the tissues below (fig.
The phellogen may arise, in the first place, in any tissue of the axis external to the actual vascular tissuesi.e.
The phellogen derives its name from the fact that its external product is the characteristic tissue known as cork.
The extent of development of the phelloderm is dependent upon whether the phellogen has a superficial or a deep-seated origin.
A peculiar modification of periderm is formed by the phellogen in the submerged organs (roots or stems) of many aquatic or marsh-loving plants.