Botany lecture notes

Complex Tissue System in Plants: Part 2 – Phloem – Structure, Components and Classification (with PPT)

cell types in phloem

Structure, Composition & Classification of Primary and Secondary Phloem

What is phloem?

Phloem is a complex tissue system in plants. It is the food conducting tissue of vascular plants. Together with xylem, they form the vascular tissue system. The phloem composed of several types of cells among which some are living cells and some are dead. The term ‘phloem’ was introduced Nageli (1853) from a Greek word ‘phloios’ meaning ‘bark’. The ‘bark’ is a non-technical term describing all tissue outside the secondary xylem of the plant. Botanically the bark includes secondary phloem, cortex, primary phloem and periderm. The current post describes the structure, composition and classification of phloem.

Location of phloem in plants:

Ø  Usually, the phloem is situated external to xylem.

Ø  In leaves, the phloem is located on the abaxial side (lower side).

Ø  In some plants (members of Cucurbitaceae and Convolvulaceae), the phloem is present on both external and internal to xylem. Such a vascular bundle is called bicollateral vascular bundle.

Ø  Phloem present internal to the xylem is called ‘internal phloem’ or intra-xylary phloem.

Ø  Phloem located external to the xylem is called ‘external phloem’.

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Botany lecture notes

Tyloses: Definition, Structure and Functions

tyloses definition


What are Tyloses?

Tyloses (singular – tylosis) are the balloon like outgrowth of parenchymatous cells to the lumen of tracheids or vessels of the secondary xylem. The axial and ray parenchyma of the xylem develops protrusion and these protrusions enter or invade into the lumen of tracheids or vessels through pits. This invasion of parenchyma occurs when tracheids or vessels become inactive or damaged.

Who discovered Tyloses?

Malpighi (1686) for the first time reported the ‘balloon-shaped sacs’ in the lumen of vessels of heartwood and he named it as tyloses based on the Greek word ‘Thyllen’ meaning ‘bag’ or ‘container’.

How Tyloses are Formed?

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Botany lecture notes

Complex Tissue Systems in Plants: Part-1 Xylem – Structure, Components and Classification (with PPT)

cell types in xylem

(Structure, Composition & Classification of Primary and Secondary Xylem)

What is vascular tissue?

The tissue associated with conduction of water, minerals and food materials in plants are called vascular tissue. Plants with a well-developed conductive system are thus called as ‘vascular plants’. Vascular plants are also known as ‘Tracheophyta’ (‘trachaea’ = vessels, a component of xylem, ‘phyta’= plants).

The vascular systems in plants composed of two types of tissues

(1). Xylem: Tissue for the conduction of water and minerals.

(2). Phloem: Tissue for the conduction of food materials.

Learn more: Difference between Xylem and Phloem

Both the xylem and phloem are complex tissues composed of more than one types of cells.  Xylem and phloem are closely organized in plants. The vascular bundles found in the primary structures of plants are formed by the association of xylem and phloem.

What is xylem?

The xylem is one of the conductive tissues in plants. It is a complex tissue composed of many types of cells. The term xylem was proposed by Nageli (1858) and he derived the word from a Greek word ‘xylos’ meaning wood. The main function of xylem is to conduct water and minerals from roots to leaves. The secondary xylem also provides mechanical support due to the presence of thick lignified cell wall.

What are the components or elements of xylem?

The xylem composed of four types of cells. Among these cells, some cells are living and some are dead.

The four elements of xylem are:

(1).  Tracheids

(2).  Vessels

(3).  Xylem Fibres

(4).  Xylem Parenchyma

(1). Tracheids

Tracheids are the fundamental cell type in the xylem. They are elongated tube like cells with tapering ends and chisel like in appearance. The cells are non-living at their maturity and the mature cells are empty without protoplast. They have highly lignified secondary cell wall and the cells angular and polygonal in cross section. The average length of tracheid is 5 – 6 mm. Major portions of the cell wall of tracheids are perforated with pits. They also possess pit pairs between two adjacent tracheids at their common walls. Pits may be simple circular pits or advanced bordered pits.

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Botany lecture notes

Anatomy of Dicot Stem: The Primary Structure – Key Points with PPT

Stem Structure Anatomy

Anatomy of Dicot Stem
Anatomy of the Primary Structure of Dicot Stem

“Biology is the study of complicated things that have the appearance of having been designed with a purpose….”
Richard Dawkins

Ø  The anatomy of dicot stem is studied by a T.S. (transverse section) took through the internode of the stem.

Ø  The components of cortex and stele are together known as Ground Tissue.

Ø  Anatomically the dicot stem has the following regions:

(1). Epidermis

(2). Cortex

a).  Hypodermis
b).  Outer cortex
c).   Inner cortex
d).  Endodermis

(3). Stele

a).  Pericycle
b).  Vascular bundles
c).  Medullary rays
d).  Pith

(1). Epidermis

Ø  Epidermis is the outermost layer, composed of parenchymatous cells.

Ø  Usually, epidermis composed of single layer of cells.

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Botany lecture notes

Anatomy of Monocot Stem: Key Points with PPT

ts of monocot stem

Internal Structure of Monocot Stem (Transverse Section, T.S.)

The anatomy or internal structure of a monocot stem can be studied by a Transverse Section (T.S.) taken through the internode of a monocot plant such as grass, bamboo, maize, Asparagus etc. The main difference of monocot stem from dicot stem is that, here in monocots the ground tissue is NOT differentiated into Cortex and Endodermis. The anatomical features of a typical monocot stem are summarized as key points below:

@. The T.S. of a monocot stem is usually circular in outline

@. Typically a monocot stem consist of FOUR tissue systems.

(1).  Dermal tissue system

(2).  Hypodermal tissue system

(3). Ground tissue system

(4). Vascular tissue system

(1). Dermal tissue system

@. Dermal tissue system constitute the epidermis

@. Epidermis forms the outermost layer

@. Usually the epidermis is single layered and made up of parenchymatous cells

@. Epidermal cells are compactly packed without any inter-cellular spaces

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