Question

An example of monocots showing secondary growth in stems is
A.Lilium
B.Cocos
C.Asparagus
D.Yucca or Dracaena

Answer 1

In monocots, the stem does not have primary cambium in the vascular bundles. Nonetheless, with age, the tree fills in the distance across vascular cambium however gradually because of the development of the ground tissue.

Complete answer: Anatomy of monocot stem:
1. Epidermis- It is a single layer of compactly arranged cells.
It does not bear trichomes but has a layer of cuticle on its external surface.
2. Hypodermis- Just below the epidermis, two to three layers of sclerenchyma cells constitute the hypodermis.
3. Ground tissue- It is not separated into cortex and pith, it is parenchymatous.
4. Vascular Bundle- Scattered vascular bundles.
Towards the periphery are smaller and those towards the center are larger.
Surrounded by sclerenchymatous bundle sheath.
Each bundle is conjoint and closed.
There are two metaxylem elements and a protoxylem element, arranged in the form of Y.
A protoxylem lacuna is characteristically present in a monocot stem.
Phloem parenchyma is absent.
Xylem is an endarch.
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Palm, Yucca, or Dracaena -Monocots capable of increase in girth.
Their tree is a monocot plant and like all other monocots, the stem does not have primary cambium in the vascular bundles. Nonetheless, with age, the tree fills in the distance across vascular cambium however gradually because of the development of the ground tissue. An auxiliary cambium might be formed in the hypodermal region of the stem. The latter forms the conjunctive tissue and patches of meristematic cells. The activity of the meristematic cells results in the formation of secondary vascular bundles.

Note: Anatomy of Dicot stem:
1. Epidermis- It is made up of a single layer of compactly arranged cells.
It Bears multicellular trichomes and externally it has a layer of cuticle.
2. Hypodermis- It is present just below the epidermis, two to three layers of collenchyma cells constitute the hypodermis.
It provides mechanical support to the young stem.
3. Cortex- It is present below the hypodermis, two or three layers of cells are sclerenchymatous.
The inner cortex is made up of parenchyma cells, which store starch grains.
4. Endodermis- It is the innermost layer of the cortex also called a starch sheath.
5. Pericycle- It is sclerenchymatous and occurs over the vascular bundles only, in the form of bundle caps.
6. Vascular Bundle- Are arranged in the form of a ring, each bundle is conjoint and open.
Xylem is an endarch.
7. Medullary rays- These are the regions in between vascular bundles, which connect the pith and the cortex; medullary rays are composed of elongated parenchyma cells.
8. Pith- It is the central part of the stem, made up of parenchyma cells.