Tag: internal structure of dicot stem

Hypodermis is a region lying immediately below the epidermis. It is represented by a few layers of collenchyma cells with angular thickenings in dicot stem. The cells are compactly arranged without any intercellular spaces. Hypodermis provides mechanical support and additional protection. Thus, option A is correct. 

Vascular cambium is a lateral cambium which is produced by intrafascicular (present between xylem and phloem) and interfascicular cambium. Vascular cambium adds phloem or xylem mother cell that differentiates into their respective cell types, thus, it causes secondary stellar growth. Hypodermis, the cortical cells present just beneath the epidermis, resume the meristematic activity and produce phellogen just beneath the epidermis. Phellogen is the extrastelar lateral meristem that produces extrasteler secondary tissue system. The cork cambium or phellogen produces phelloderm on inside and phellem or cork on outside thereby adding extrastelar secondary tissues.
Therefore, the correct answer is option B.

Monocot plants cannot be grafted as they lack the cambium tissue which is present in dicot plants. Cambium tissue is a meristematic tissue which is present in the vascular bundles of the dicot plants. This tissue has a regeneration capacity due to which it can form new tissue at the time of grafting. The lack of cambium in monocots makes it impossible to graft. Grafting or graftage is a technique used in horticulture that consists of taking tissues from one plant and putting them onto another plant. The two plants will then grow together.
The technique is a type of vegetative reproduction. Grafting is commonly used with roses, and fruit trees. It only works with dicots and gymnosperms and not with monocots. Monocots do not have a vascular cambium, which is needed for the process to work. 
Thus, the correct answer is option B.

Phellem is outermost layer of cork cambium, which is suberised. Hence, this is the first layer to be found. 
Endodermis is one the layer of cortex, which is to be found under the phellem.
Pericycle is the layer present between endodermis and vascular bundles. 
Dicotyledonous stem possess conjoint, collateral vascular bundle, where xylem is internal and phloem is external. Therefore, phloem is to be encountered after the pericycle. 

Cork cambium is the extrastelar lateral meristem that produces extrasteler secondary tissue system. Cortex is the ground tissue which surrounds the central stele and is derived from ground meristem. Hypodermis refers to 5-7 layers of cortical cells present just beneath the epidermis which resume the meristematic activity and produce phellogen or cork cambium just beneath the epidermis. The outer most covering of stele forms pericycle, it is an intrasteler tissues present in a stele which means that phellogen (extrastelar lateral meristem) cannot be produced by pericycle. The phellogen or cork cambium produces cork or phellem towards the periphery and phelloderm towards inner side. As phellem and phelloderm are the product of cork cambium, not its progenitor. 
Thus, the correct answer is option A.

Lenticel is a pore in the stem of a woody plant, showing a raised spot that may be filled with a powdery substance. The pore permits air to reach tissue below the surface. Stomata are present in leaves, Sieve plates are present in phloem tissue for the transport of carbohydrates and Pits are the characteristic depressions on the cell walls for the transport of water and minerals.

During secondary growth, rupturing of epidermal cell and outer cortex by secondary tissues induces formation of new protective layer, periderm turning the single layered pericycle into multi layered meristem that divides to form cork cambium or phellogen. The cork cambium exhibit meristematic activity and produces cork or phellem towards the periphery and phelloderm on inside, i.e., extrastellar growth. Moving from centre to periphery, a dicot root has pith, secondary xylem, secondary phloem, phelloderm (secondary cortex), phellogen (cork cambium), cork (phellem) and bark. Since, primary cortex is ruptured and is not present in secondary root. Cork is extra stellar tissues which is present outside the stele (vascular bundle, pith and medullary rays surrounded by pericycle) region and hence, cannot be present inner to endodermis.
Thus, the correct answer is option B.

The parenchyma in the centre is called as the pith. The term stele included the vascular system, associated tissues and the pith. The protostele is a simple, unbranched, centrally located axial strand of xylem interspersed with phloem. A protostele contains no pith. It is generally found in dicot stems and in most angiosperm monocot roots.

The hypodermis is found below the epidermis in dicot stem and is constituted with angular collenchyma which is 3-5 layered. Pericycle consists of alternately arranged patches of sclerenchyma and parenchyma. 
Thus, the correct answer is option C.