Question

The term ‘‘bark’’ means:
A. Phellem, phelloderm and vascular cambium
B. Phellem, phellogen, phelloderm and secondary phloem
C. Periderm and secondary xylem
D. Cork cambium and cork

Answer 1

Hint: All the tissues present outer to the vascular cambium constitute the Bark.

Complete step-by-step answer:
1. All the tissues present outer to the vascular cambium together is called the Bark. This includes the phellem, phelloderm, and secondary phloem.
2. The bark is found in dicot stems of flowering plants only.
3. The bark is a non-technical term that refers to all the tissues external to the vascular cambium, this includes the secondary phloem.
4. At certain regions in the bark’s exterior, the phellogen cuts off closely arranged parenchymatous cells on the outer side instead of forming cork cells. These parenchymatous cells inadvertently rupture the epidermis, forming a lens-shaped opening called the lenticels. Lenticels permit the exchange of gases between the outer atmosphere and the internal tissue of the stem. These occur in most of the woody trees.
5. The bark in general is covered by a hydro-repellent substance known as suberin
6. Phellogen is also known as the cork cambium. It is a layer of meristematic tissue that is formed as the stem continues to increase in girth due to the proliferative activity of the vascular cambium, the outer cortical and epidermis layers get broken and need to be replaced to provide new protective cell layers from the inner tender parts.
7. Phellem is also known as the cork.
8. Phelloderm is also known as the secondary cortex.
9. Secondary phloem are the cells cut off towards the periphery by the activity of the cambial ring.

So, the correct answer is “Option 2: Phellem, phellogen, phelloderm and secondary phloem ”.

Note:
1. The bark that is formed early in the season is called early or soft bark. The bark that is formed towards the end of the season is known as the late or hard bark is formed.
2. The bark also helps to translocate the sugars created in the leaves to other parts of the plant for storage.