Cork cambium undergoes periclinal division and cuts off thick walled suberised dead cells towards outside i.e. phellem (cork) and it cuts off thin walled living cells i.e., phelloderm on inner side.
Tyloses are balloon-like extensions of parenchyma cells that protrudes into the lumen of a neighbouring xylem vessel or tracheid through a pit in the cell wall.
Tyloses form most commonly in older woody tissue, possibly in response to injury, they may eventually block the vessels and thus prevent the spread of fungi and other pathogens within the plant.
Tyloses may become filled with tannins, gums, pigments, etc., giving heartwood its dark colour, and their walls can remain thin or become lignified.
In botanical terms, the cortex of a plant is the region found between the epidermis and the stele.
Therefore, the correct answer is: Option C: Epidermis and stele.
To clarify: Epidermis: This is the outermost layer of cells in the plant stem and root.
It serves as a protective barrier against the external environment.
Stele: This is the central part of the root or stem, containing the vascular tissue (xylem and phloem), pith, and often a pericycle.
The stele is located inside the endodermis.
The cortex lies between these two layers, functioning mainly in storage and transport of nutrients and water.
It is composed primarily of parenchyma cells and is a significant part of the root and stem where it often stores starch.
The other options refer to different parts of the plant anatomy: Option A: Endodermis and pith - The pith is located in the center of the stem, surrounded by the vascular tissue, which is inside the endodermis.
The cortex is not between these two.
Option B: Endodermis and vascular bundle - The endodermis is a single layer of cells forming a boundary between the cortex and the stele; it doesn't define the boundaries of the cortex.
Option D: Pericycle and endodermis - The pericycle is a layer of cells found just inside the endodermis, and it is part of the stele.
This option does not correctly describe the position of the cortex.
Thus, Option C is the most accurate in describing the location of the cortex in a plant.
Specialized epidermal cells surrounding the guard cells are known as Subsidiary or accessory cell.
In monocot root, a large number of vascular bundles are arranged in the form of a ring around the central pith.
Vascular bundles are closed because there is no cambium present between the xylem and phloem.
Vascular bundles in monocotyledons (plants with a single seed leaf, like grasses and grains) are considered closed primarily due to Option D: Cambium is absent.
In botany, vascular bundles are the part of the plant that transport nutrients and water.
In monocotyledons, these bundles are typically scattered throughout the stem and do not have a cambium layer.
The cambium is a layer of actively dividing cells found in most dicotyledons (plants with two seed leaves) and is responsible for secondary growth, which includes the widening of the stems and roots.
This secondary growth is possible because the cambium adds layers of vascular tissue called secondary xylem (wood) and secondary phloem.
In monocotyledons, the absence of cambium means there's no secondary growth, and thus, the vascular bundles are termed closed.
This is different from open vascular bundles found in dicotyledons, where the presence of cambium allows for continuous growth and change in the arrangement of the xylem and phloem.
Options A, B, and C describe other aspects of vascular bundles but are not the reasons why monocotyledonous vascular bundles are considered closed.
For instance: Option A: The presence or absence of vessels with perforations is more about the type of vessels in the xylem and not directly related to the concept of open or closed vascular bundles.
Option B: While xylem surrounded by phloem is a characteristic of some vascular bundles, it doesn't define them as open or closed.
Option C: A bundle sheath may be present in both monocotyledons and dicotyledons and is not a defining factor for open or closed vascular bundles.
Therefore, Option D, Cambium is absent, is the correct reason for vascular bundles in monocotyledons being considered closed.
Anatomically fairly old dicotyledonous root is distinguished from the dicotyledonous stem by position of the protoxylem.
In dicot root, the protoxylem is located near the periphery of the vascular cylinder while in dicot stem the protoxylem is located near the centre of vascular bundle i.e., the xylem is endarch.
The walls of vessels (tracheary elements) are lignified and less thicker than tracheids.
The lumen is wider.
Vessels differ from tracheids in having cell fusions arising through the dissolution of end walls.
C 4 plants show kranz type of anatomy.
In kranz anatomy, the mesophyll is undifferentiated and its cells occur in concentric layers around vascular bundles.
The vascular bundles are surrounded by large sized bundle sheath cells which are arranged in wreath like manner in one to several layers.
In C 4 plants there are two carboxylation reactions, first in mesophyll chloroplast and second in bundle sheath chloroplast.
RuBP is present in bundle sheath chloroplasts where C 3 cycle takes place.
Lateral meristems are meristems which occur parallel to the circumference of the organs in which they develop.
They undergo periclinal divisions producing secondary tissues on the outer and inner sides and increase the girth of the plant organs.
Examples are vascular cambium and corkcambium.
