Question

Is phellem produced by phellogen?

Answer 1

Both phellem and phellogen are actually parts that develop from the cork cambium. The cork cambium is a lateral meristem and is responsible for secondary growth that replaces the epidermis in roots and stems. It forms one of the many layers of the bark, between the cork and primary phloem. It is found in woody and many herbaceous dicots, gymnosperms and some monocots (monocots usually lack secondary growth).

Complete answer:
As the stem continues to increase in girth due to the activity of the vascular cambium, the outer cortical and epidermis layers get broken and need to be replaced to provide new protective cell layers. Hence, another meristematic tissue called cork cambium or phellogen develops.
Phellogen is a double layered ring-shaped structure made up of narrow, thin-walled and nearly rectangular cells. The phellogen cuts off cells from both sides. The outer cells differentiate into cork or phellem, while the inner cells differentiate into secondary cortex or phelloderm.
Phellogen, phellem, and phelloderm are collectively known as periderm.
Thus, we learned that phellogen is actually cork cambium and the cells which differentiate outwards are known as phellems. So, it is evident that phellem is produced by phellogen.

Note:
Due to the activity of the cork cambium, pressure builds up on the remaining layers peripheral to phellogen and ultimately these layers die and slough off. This means that the phellem is composed of dead layers of cells. The cork is impervious to water due to suberin deposition in the cell wall. The cells of the secondary cortex or phelloderm are living and parenchymatous.