Internal Structure of Dicot Stems

In dicot stem, the lateral branches are exogenous in origin and they come out from the cortex of the stem. However, in dicot root, the lateral roots are endogenous in origin because they come out from the pericycle of the stem.

In a young dicot stem, the cambium is single layered. It is made by the intrafascicular cambium present within the vascular bundles and the dedifferentiation of the parenchyma cells of the medullary rays between the vascular bundles, called interfascicular cambium. Their combination gives a circular cambium that produces xylem elements on the inner side and the phloem elements on the outer side.

Cork cambium is secondary or lateral meristematic tissue that grows beneath the epidermis and replaces it in dicot roots and stems and is responsible for the secondary growth of the tree.

The pericycle is a thin layer located between the endodermis and phloem in plant roots. In dicot stems, it is located around the ring of vascular bundles in the stele. The nature of pericycle is sclrenchymatous. 

Bast fibers are made up of sclerenchymatous cells and are absent in primary phloem but present in secondary phloem of dicots and are elongated , unbranched and have pointed needle like apices and are devoid pf protoplasm at maturity and dead.

• Pericycle is a cylinder of parenchymal and sclerenchyma cells which lie just below the endodermis of the plants. 
• In dicot stem, the pericycle is heterogenous made of parenchyma and sclerenchyma alternatively in irregular patches but they are not multilayered.
• So, the correct answer is 'In a dicot stem, the pericycle is usually multilayered'.

In a typical dicot stem anatomy, the vascular bundles are conjoint, open (having cambium allowing secondary growth), and arranged in a ring. Statement C incorrectly states they are closed.

Casparian strips occur in radial walls of endodermis. The Casparian strip is a band of cell wall material deposited on the radial and transverse walls of the endodermis, and is chemically different from the rest of the cell wall - the cell wall being made of lignin and without suberin - whereas, the Casparian strip is made of suberin and sometimes lignin. It blocks the passive flow of materials such as water and solutes into the stele of a plant.
Thus, the correct answer is option A.

Open vascular bundle contains an interfascicular cambium in between phloem and xylem. Phloem and xylem are not in direct contact with each other. 

Starch sheath is endodermis of dicot stem. The endodermis is the central, innermost layer of cortex in some land plants. The endodermis is the boundary between the cortex and the stele. The endodermis helps regulate the movement of water, ions and hormones into and out of the vascular system. It may also store starch, be involved in perception of gravity and protect the plant against toxins moving into the vascular system. 

In dicot stems, the pith is generally small or reduced compared to monocot stems, where it is often large and well-developed. Dicot roots typically lack a pith or have a very small one.

In a dicot stem, by the end of the first year, the primary structure shows the growth of vascular and cork cambiums. The growth of the secondary xylem becomes continuous with the primary xylem. The secondary growth occurs both in the stele and cortex and though simultaneously, is caused by separate strips of
secondary meristem. The cambial ring exhibits mitotic activity on both the sides and ones towards the inner surface results in the formation of xylem cells.

Hypodermis is a region lying immediately below the epidermis. It is represented by a few layers of collenchyma cells with angular thickenings. The cells are compactly arranged without any intercellular spaces. Hypodermis provides mechanical support and additional protection. So, hypodermis of a dicot stem is composed of collenchyma and not parenchyma or sclerenchyma. 
Thus, the correct answer is option B.

In a young dicot stem epidermis is covered by a waxy coating, called as cuticle. Cuticle is the waxy coating of the outer walls of epidermal cells of stem. It's function is to protect against excessive water loss, as well as protecting against mechanical injury.

Collenchyma tissue is composed of elongated cells with irregularly thickened walls. They provide structural support, particularly in growing shoots and leaves. Collenchyma tissue makes up things such as the resilient strands in stalks of celery. Collenchyma cells are usually living and have only a thick primary cell wall made up of cellulose and pectin. Cell wall thickness is strongly affected by mechanical stress upon the plant. The walls of collenchyma in shaken plants may be 40 to 100% thicker than those not shaken. Collenchyma cells are most often found adjacent to outer growing tissues such as the vascular cambium and are known for increasing structural support and integrity. So, stem of few dicot plants are getting mechanical strength mainly because of collenchyma before secondary growth. Parenchyma is a versatile ground tissue that generally constitutes the filler tissue in soft parts of plants. It forms, among other things, the cortex and pith of stems, the cortex of roots, the mesophyll of leaves, the pulp of fruits and the endosperm of seeds. Sclerenchyma is the supporting tissue in plants after secondary growth. 
Thus, the correct answer is option B.

As we know that Intrafascicular or intrastelar cambium is present between xylem and phloem in dicot stem and roots. Pith rays, present between the edges of intrafascicular cambium, divide to form a new cambium strip between the two vascular bundle i.e. interfascicular cambium. Thus, inter and intra fascicular cambium together forms a complete cambium ring called as vascular cambium or just cambium which forms secondary xylem on inner side and secondary phloem on outer side. Differential cambial activity during autumn and spring season result in narrow and wide secondary xylem rings respectively which together forms the annual growth ring. Thus annual growth ring is derived from vascular cambium which is derived from inter and intrastelar cambium.

Pith or medulla, is a tissue in the stems of vascular plants. Pith is composed of soft, spongy parenchyma cells, which store and transport nutrients throughout the plant. In dicots, pith is located in the centre of the stem. In monocots, it extends also into flowering stems and roots. The pith is encircled by a ring of xylem. The xylem, in turn, is encircled by a ring of phloem. The monocot root has a pith, whereas the dicot root does not. Absence of pith is the diagnostic feature of dicot root. Pith is present in dicot stem, monocot stem, monocot root and dicot stem. 
Thus, the correct answer is option D.

Intercalary meristem at base of leaves or nodes of grasses is responsible for  primary growth. Meristems are classified by their location in the plant as apical located at root and shoot tips, lateral in the vascular and cork cambia, and intercalary at internodes or stem regions between the places at which leaves attach, and leaf bases. Intercalary meristem cells possess the ability to divide and produce new cells, as do apical and lateral meristems. They differ, however, in being situated between regions of mature tissue, such as at the base of grass leaves, which are themselves located on mature stem tissue.
Therefore, the correct answer is option A.

Phellogen is the extrastelar lateral meristem that produces extrasteler secondary tissue system. Epidermis is the outermost covering of the primary stem that delimits cotex on outer side and is ruptured by stelar secondary growth, therefore cannot produce phellogen. 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 just beneath the epidermis. The innermost layer of cortex forms endodermis while the phellogen is produced just beneath the epidermis. The outermost 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. 
Therefore, the correct answer is option A.

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.

A. Periderm - During secondary growth in both dicot stem and root, multilayered or cellular complex tissue formed in the region of cortex is called Periderm. It is formed towards the outer side of the stem or root.

B.Epiblema – Epidermis with root hairs is called Epiblema.

C. Phelloderm – the parenchymatous formed towards inner side of the cork cambium is called phelloderm or secondary cortex.

D. Phellogen – a ring of meristematic tissue formed by the dedifferentiation of parenchyma present in the general cortex of dicot stem or root is called Phellogen or cork cambium.

So, the correct option is ‘Periderm’.

In the vascular bundles of Cucurbita stems, a xylem strand and two phloem strands are present on the same radius. So the vascular bundles are called Bicollateral vascular bundles. In these bundles, two strips of cambiua are present in between the xylem and phloem.

So, the correct option is ‘ 2’.

In dicot stem, during secondary growth, when new secondary xylem formation is going on, oldest secondary xylem appear outside the primary xylem.

The layer with thick walled present around the vascular bundles is called Bundle sheath. It is sclerenchymatous in monocot stem vascular bundles, parenchymatous in dicot leaf and monocot leaf. It is absent in vascular bundles of dicot stem

So, the correct answer is ‘Dicot stem’

A.Helianthus - a dicot with rings of vascular bundles in the stele. It is called Eustele.

In dicot stem, endodermal cells are rich in starch grains. So it is also called endodermoid layer or starch sheath or starch layer.

So, the correct option is ‘Starch sheath’.

The
corky outer layer of a plant is commonly called the periderm. It has three
parts- the cork cambium (phellogen), the cork (phellem), and the secondary
cortex (phelloderm). It usually forms as a result of secondary thickening in
the case of an injury.

• In vascular plants, the secondary growth occurs due to the activity of the two lateral meristems- the cork cambium and the vascular cambium.
  
• In woody plants, the secondary growth produces wood and gives shapes to the plant with a thickened trunk.
• The secondary growth develops a cork cambium and vascular cambium.
• The cork cambium forms the thickened cork cells which protect the surface of the plant and also reduces water loss.
• Vascular cambium is also known as fascicular cambium which develops within the vascular bundles that produce xylem to the inner side and phloem to the outer side.
• In dicots, the fascicular and interfascicular cambium combine together to form a continuous ring called the vascular cambium.
• So, the correct answer is 'Lateral meristem'

Secondary growth occurs due to cell division in cambia or lateral meristems resulting in thickening of stems and roots. This is the characteristic feature of dicotyledons, gymnosperms and vascular system plants. Teak and pine belong to these systems and study of secondary growth is possible in these plants.

Epiblema is the outer layer of the roots also known as epidermal cells of roots which perform the function of absorption.

1. Cucurbita stem: Collenchyma is the tissue of primary body. The cell walls show localized thickenings. It occurs chiefly in the hypodermis of dicot stems( e.g. Cucurbita, Helianthus).
   2. Potato tuber: Parenchyma is cell and tissue type in which the cells have only thin primary walls. The cotyledon of many leguminous plants contains protein and starch in their parenchyma cells. Protein and starch are present in the parenchyma of potato tuber.
   3. Walnut shell: Sclerenchyma consists of thick-walled dead cells. It usually occurs in hard parts of plant bodye.g. hard endocarp of Walnut, almond and coconut).
   4. Jute fibres: Phloem fibres are also called bast fibres and most occur in secondary phloem. The fibres of primary phloem have both cellulose and lignified thickenings.
   So, the correct answer is 'Collenchymatous hypodermis, Parenchyma, Sclerenchyma, Phloem'.

More distinct annual rings are formed in that regions, where climatic variations are sharp. More distinct annual rings are formed in temperate plants as the climatic conditions of temperate regions are not uniform.

The cells of the seive tube elements contains protoplasm. a large vacuole however nucleus is lost at maturity. The conduction of food material takes between the cells through seive plants. The flow of food (sucrose), its loading etc is controlled by companion cells. Each seive tube cell is associated with one companion cell.

Hypodermis is a distinctive layer of mechanical tissue present in some dicot and monocot stems. It is collenchymatous and present as 3-4 layers. It provides mechanical support and elasticity, also stores food.

Cortex is the outermost layer of the stem or root of the plant. It is surrounded by a parenchymatous layer. The cortex is unspecialized cells which help as conducting tissue in the plants.

Peripheral vascular bundles are generally smaller than the centrally located ones because the phloem parenchyma is absent and the water containing cavities are present in the vascular bundles which are both in monocot and dicot stem.

Most of the features of the dicot and monocot roots are similar except the vascular bundles. In the dicot root, there are 2-6 bundles of xylem and phloem alternating whereas in monocots the number of xylem and phloem strands are more than 8. Further, the xylem vessels in dicots are polygonal and those of monocots are oval.

• In dicot stem, the secondary vascular tissues originate as a result of the cambial activity. 
• The cambial cells divide tangentially again and again and produce secondary tissues. 
• Some of the cells of single-layered pericycle become meristematic, which divides and form a few layers of cells, phellogen.
• Hence, In a dicot stem, pericycle gives rise to Phellogen.
• So, the correct answer is 'Phellogen'.

Knots are common blemishes in trees, often causing lumps or holes within the trunk of the tree itself. In most cases knots are caused by the natural growth of the tree, though the specific circumstances under which they form determines how they will appear. As a tree grows and increases the circumference of its trunk, the growing trunk begins to overtake the branches that grow out from it. Knots form around these branches, building up trunk material as the tree continues to expand. Since, the branches are still growing as they are overtaken by the trunk, the knot that forms is solid and contains living wood throughout. The wood of the knot is typically tougher than the surrounding wood and may form a bulge around the branch emerging from its center. So, knots are formed in wood due to bases of the branches get buried in main stem and not because leaf scars, insect bites and injuries. 
Therefore, 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. Hence, option C is correct. 

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

Dicot stem vascular bundles are eight in number, arranged in form of a broken ring. The vascular bundles are conjoint, collateral and open. Xylem is on the inner surface and phloem on the outer surface. Xylem is described as endarch. 

In dicot stem, hypodermis is a region lying immediately below the epidermis. It is represented by a few layers of collenchyma cells with angular thickenings. The cells are compactly arranged without any intercellular spaces. Hypodermis provides mechanical support and additional protection. Phellogen is the secondary lateral meristem that may arise from permanant living cells of hypodermis or outer cortex. It is composed of single layer of meristematic cells. 

Dicot stem vascular bundles are eight in number, arranged in form of a broken ring. The vascular bundles are conjoint, collateral and open. Xylem is on the inner surface and phloem on the outer surface. Xylem is described as endarch. 

Intrafascicular cambium is present between xylem and phloem in dicot stem. It is also termed as fascicular cambium. This meristematic area spreads laterally from each bundle and eventually becomes continuous, forming a complete vascular cambium.

Endarch is the arrangement in which the protoxylem is directed towards the centre and metaxylem elements towards the periphery. The development of the xylems in this arrangement follows the centrifugal pattern. It is the characteristics of the stem of flowering plants.

Whereas exarch is the arrangement in which the protoxylem is directed towards the periphery and metaxylem towards the centre. The development of the xylem in this arrangement follows the centripetal pattern. It is the characteristics of roots.

In dicot stem during secondary growth, the oldest part of xylem situated towards outer to the medulla and oldest phloem is situated just towards inner to the primary cortex.

So, the correct option is ‘Inner to primary cortex’.

A. Root – protoxylem is towards the pericycle and metaxylem is towards the medulla. It is called Exarch.

B. Stem – protoxylem is towards the medulla and metaxylem is towards the pericycle. It is called Endarch.

C. Leaves – the position of protoxylem and metaxylem is not specified.

D. Petiole – the position of protoxylem and metaxylem is not specified.

So, the correct option is ‘stem’.

Pericycle is the outer most part of the stele. In dicot, stem pericycle is, sclerenchymatous, discontinuous, multilayered and present in the form of patches over the vascular bundles.

So, the correct option is ‘Multilayered’.

In dicotyledonous trees, growing in temperate regions, due to maximum seasonal variations two types of secondary xylems are formed, spring or early wood and autumn wood or latewood. These two kinds of wood together form into a ring of wood called annual rings. These annual rings are useful in indicating the age of the trees.

So, the correct option is ‘Dicot of temperate regions’.

Cortex is middle region of the root and dicot stem, present between epidermis and stele.

So, the correct option is 'epidermis and stele'.

A.Vascular bundles arranged in a ring – found in T.s. of dicot stem

B.Scattered vascular bundles – found in T.s.of monocot stem

C.Closed vascular bundles – found in T.s.of monocot stem

D.Radial vascular bundles – found in T.s.of dicot and monocot roots.

So, the correct option is ‘Vascular bundles arranged in a ring’.

A. Conduction of water – xylem conducts water.

B.Storage of water – water storage parenchyma

C.Storage of food – cortex stores reserve food materials.

D. Strength – hypodermis and pericycle in dicot stem provides strength.

So, the correct option is ‘Storage of food’.

A.Pericycle – outer most part of the stele in roots and dicot stem.

B.Endodermis – innermost part of cortex in roots and dicot stem.

C. Cutinised – The outer walls of stem epidermal cells are cutinized i.e.covered by the cuticle.

D.Suberised – The walls of cork cells are suberized i.e. made up of suberin.

So, the correct option is ‘Endodermis’.

A.Apical meristem – meristem present in the apices of plant parts, found in all higher plants.

B.Primary meristem – meristem formed from embryonic tissues or promeristem. eg:Fascicular cambium – found in dicotyledons

C.Secondary meristem – meristem formed by the dedifferentiation of permanent tissues. eg:Inter fascicular cambium, cork cambium- found in dicotyledons

D.Intercalary meristem – meristem present in between permanent tissues, found in monocotyledons

So, the correct option is ‘Primary meristem’.     

In dicotyledonous stems of temperate trees, during secondary growth, vascular cambial ring(narrow layer of thin-walled cells) produces secondary phloem towards outer side and secondary xylem or wood towards inner side.

So, the correct option is ‘vascular cambium’.

A.Polyarch – stele with many xylem strands, is found in monocot roots.

B.Monoarch – stele with one xylem strand, is found in Trapa.

C.Endarch – protoxylem is present towards the centre, and metaxylem is present towards the periphery, is found in dicot and monocot stems.

D.Exarch – protoxylem is towards the periphery, metaxylem is towards the centre, is found in dicot and monocot roots.

So, the correct option is ‘Endarch’.

Latex is a milky white secretory material. It is secreted by a special tissue  called are Laticiferous tissues. These are found in the plants growing in tropical deciduous forests. These are present in two types, namely latex cells and latex vessels. Latex is used in the manufacture of rubber. In the plants

A-The outer light coloured, functional secondary xylem or wood, takes up in the conduction of water of sap is called sapwood or alburnum.

The anatomy of dicot root and dicot stem differ in many characters. In dicot, root epidermis contains root hairs, whereas in epidermis contains trichomes, cuticle and stomata. In dicot, root cortex shows general cortex and endodermis, whereas in dicot stem cortex shows hypodermis, general cortex and endodermis.

In dicot, root hypodermis is absent whereas, in dicot stem, hypodermis is present.

In dicot root endodermis shows Casparian bands, whereas in dicot stem endodermis contains starch grains in its cells.

In dicot root pericycle is parenchymatous, take part in the lateral formation and secondary growth, whereas in dicot stem, pericycle is discontinuous, sclerenchymatous, present in the form of patches over the vascular bundles.

In dicot root, vascular bundles are radial, whereas in dicot stem vascular bundles are collateral, conjoint, open

In dicot, root xylem is exarch, whereas in dicot stem xylem is endarch.

In dicot, root medulla is reduced, whereas in dicot stem is xylem is endarch.

In dicot root, conjunctive tissue is present, whereas, in dicot stem, medullary rays are present.

So, the correct option is ‘Protoxylem’

a) Collenchymatous hypodermis -applicable because hypodermis is made up of collenchyma.

b) Polyarch xylem – not applicable, because, xylem and phloem are present on the same radius and side by side. It is found in monocot roots.

c) Presence of Casparian strips on endodermis – not applicable, because Casparian strips appear on the radial and tangential walls of the endodermis of roots.

d) Open vascular bundle – applicable, because, cambium is present between the xylem and phloem in the vascular bundles.

e) Presence of medullary rays – applicable – because, these are the extensions of medulla between the vascular bundles.

So, the correct option is ‘b and c’.

secondary xylem is also called wood. Any tissue located to the "outside" of the vascular cambium is considered bark and tissue side is called as wood.