Phloem,Sieve tubes,Companion cells,Pholem parenchyma,Phloem fibres,Translocation of Organic food,Cytoplasm and a Prominent, Plasmodesmata

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Home >> Biology >> Morphology and Anatomy of Flowering Plants >> Complex Tissues - Phloem

Phloem
It is also called bast and consists of four types of cells ¾
1. Sieve tubes,
2. Companion cells,
3. Phloem parenchyma,
4. Pholem fibres.
It is meant for conduction of organic food inside the plant body.

sieve-tub-members-in-transverse-and-longitudinal-sections-respectively
Sieve Tub Members in Transverse and Longitudinal Sections Respectively

A - Sieve Plate	C. Fibre
B. Companion Cells	D. Sieve Plate E - Sieve Plate


Pholem Tissue

[A-B. sieve tube members in transverse and longitudinal sections respectively. C. sieve plate. D. sclereid. E. pholem parenchyma cell. F-G unseptate and septate phloem fibres respectively.]

1. Sieve tubes
These are elongated tubular living cells with thin walls made up of cellulose. Cells possess transverse walls and are placed end to end. The pores are present on end walls forming sieve plates and also along lateral wall forming sieve areas. These pores from continuous channels for translocation of organic food. Young sieve tube has nucleus which disintegrates at maturity and develop large vacuole. At this stage its activity is regulated by adjacent companion cells.

2. Companion cells
These are thin walled cells associated with sieve tubes, assisting them in conduction of food. They have a dense cytoplasm and a prominent nucleus. It is connected to sieve tubes by plasmodesmata. Thus they control the activity of sieve tubes through plasmodesmata. The companion cells are present only in angiosperms.

3. Pholem parenchyma
These are parenchymatous cells present in pholem which store food and assist in its conduction in radial directions.

A sieve Tube Number with Compound Sieve Plate A - Compound Sieve Plate B - Lateral Sieve Area C - Companion Cell	Compound Sieve Plate in Surface View, Magnified A - Sieve Area B - Compound Sieve Plate
Phloem Tissue from the Stem of Nicotiana Tabacum Showing Sieve Tubes, Companion Cell and Phloem Parenchyma

4. Phloem fibres
These are sclerenchymatous cells found mainly in secondary pholem. They are highly lignified and provide mechanical strength to pholem.

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Anatomy of Flowering Plants Tissue and Meristematic Tissue Classification of Meristematic Tissue Apical Meristems of Stem and Root Permanent Tissue Simple Permanent Tissue Complex Tissues - Xylem Types of Xylum Complex Tissues - Phloem Classification of Permanent Tissue on Basis of Their Functions Types of Vascular Bundles Anatomy of Monocot Stem - Maize, Primary Structure of Stem Anatomy of Dicotyledonous Stem - Sunflower Stem Secondary Growth in Dicot System Origin and Activity of Cambium Origin and Activity of Cork Cambium Heart Wood and Sap Wood Primary Structure of Monocot Root Primary Structure of Dicot Root Secondary Growth in Dicot Roots Origin and Activity of Vascular Cambium Origin and Activity of Cork Cambiums Internal Structure of Dicot Leaf Internal Structure of Xerophytic Leaf Internal Structure of Monocot Leaf - Isobilateral Leaf