plant anatomy-Permanent tissue/ simple and complex tissue, xylem, phloem,parenchyma

1. VIMAL PRIYA subramanian

2. Permanent tissue
The permanent tissues may be simple or complex.
A simple tissue is made up of one type of cells forming a uniform or
homogeneous system of cells.
The common simple tissues are parenchyma, collenchyma and
sclerenchyma.
A complex tissue is composed of more than one type of cells working
together as a unit.
The complex tissues consist of parenchymatous and sclerenchymatous
cells; collenchymatous cells are not present in such tissues. The common
instances are—the xylem and the phloem.

6. Parenchyma:
The parenchyma tissue is made-up of living cells which are variable in their
morphology and physiology, but generally having thin walls and a polyhedral
shape, and concerned with vegetative activities of the plant. The individual cells
are called parenchyma cells.
The parenchyma includes isodiametric, thin-walled and equally expanded cells.
The parenchyma cells are oval, rounded or polygonal in shape having well
evolved spaces among them. The cells are not greatly elongated in any
direction. The cells of this tissue are living and contain sufficient amount of
cytoplasm in them. Usually each cell contains one or more nuclei.

7. Parenchyma

8. • Parenchyma makes up large parts of various organs in several plants.
Pith, mesophyll of leaves, the pulp of fruits, endosperm of seeds, cortex
of stems and roots, and other organs of plants consists mainly of
parenchyma. The parenchyma cells also exist in xylem and phloem.
• In the aquatic plants, the parenchyma cells in the cortex contain well
developed air spaces (intercellular spaces) and such tissue is known as
aerenchyma. Parenchyma may be specialized as water storage tissue in
many succulent and xerophytic plants.
• In several plants, chlorophyll-free, thin-walled and water-turgid cells are
found which represent water storage tissue. When the parenchyma cells
are exposed to light they develop chloroplasts in them, and this tissue is
known as chlorenchyma. The chlorenchyma contains well developed
aerating system. Intercellular spaces are abundant in the photosynthetic
parenchyma (chlorenchyma) of stems too.

9. Cont..

10. • The turgid parenchyma cells help in giving rigidity to the plant body.
• Partial conduction of water is also maintained through parenchymatous
cells. The parenchyma acts as special storage tissues to store food
material in the form of starch grains, proteins, fats and oils.
• The parenchyma cells that possess chloroplasts in them make
chlorenchyma which are responsible for photosynthesis in green plants.
In water plants the aerenchyma keep up the buoyancy of the plants.
• These air spaces also facilitate exchange of gases. In many succulent
and xerophytic plants this tissues store water and are known as water
storage tissue.
• Vegetative propagation by cuttings takes place because of meristematic
potentialities of the parenchyma cells which divide and evolve into buds
and adventitious roots.

11. Collenchyma
# Collenchyma is a living tissue made –up of somewhat elongated cells
with thick primary non-lignified walls.
# Important characteristics of this tissue are its early evolution and its
adaptability to change in the rapidly growing organ, especially those of
increases in length.
# When the collenchyma becomes functional, no other strongly
supporting tissues have appeared.
# It gives support to the growing organs which do not evolve much
woody tissue. Morphologically, collenchyma is a simple tissue, for it
consists of one type of cells.

12. Collenchyma

13. Cont..
• Collenchyma is a typical supporting tissue of growing organs and of those
mature herbaceous organs which are only slightly modified by secondary
growth or lack this growth completely.
• It is the first supporting tissue in stems, leaves and floral parts.
• It is the main supporting tissue in many dicotyledonous leaves and stems of
monocotyledons.
• Collenchyma chiefly exists in the peripheral regions of stems and leaves. It is
commonly found just beneath the epidermis.
• In stems and petioles with ridges, collenchyma is particularly well developed
in the ridges. In leaves it can be differentiated on one or both sides of the
veins and along the margins of the leaf blade.

14. Cont..
• The collenchyma includes elongated cells, various in shape, with unevenly
thickened walls, rectangular, oblique or tapering ends, and persistent
protoplasts.
• The cells overlap and interlock, forming fibre like strands.
• The cell walls include cellulose and pectin and have high water content.
• They are extensible, plastic and adapted to rapid growth. In the beginning the
strands are of small diameter but they are added to, as growth continues,
from surrounding meristematic tissue.
• The border cells of the strands can be transitional in structure, passing into
the parenchyma type.
• The walls of collenchyma are chiefly composed of cellulose and pectic
compounds and contain much water. In several plants collenchyma is a
compact tissue lacking intercellular spaces.

15. Cont..
• The mature collenchyma cells are living and contain protoplasts.
Chloroplasts also exist in variable numbers.
• They are found abundantly in collenchyma which approaches
parenchyma in form.
• Collenchyma consisting of narrow cells possesses only a few small
chloroplasts or none.
• Tannins can be present in collenchyma cells.
• The chief primary function of the tissue is to give support to the plant
body. Its supporting value is increased by its peripheral position in the
parts of stems, petioles and leaf mid-ribs. When the chloroplasts are
present in the tissue, they carry on photosynthesis.

16. Sclerenchyma

17. Sclerenchyma
# The sclerenchyma (Greek sclerous = hard; enchyma = an infusion) includes
thick-walled cells, often lignified, whose major function is mechanical.
# This is a supporting tissue that withstands various strains which result from
stretching and bending of plant organs without any damage to the thin-
walled softer cells.
#The individual cells of sclerenchyma are called sclerenchyma cells.
Collectively sclerenchyma cells make sclerenchyma tissue. Sclerenchyma
cells do not contain living protoplasts at maturity.
#The walls of these cells are uniformly and strongly thickened. Most
commonly, the sclerenchyma cells are grouped into fibres and sclereids.

18. Fibre
The fibres are elongate sclarenchyma cells, generally with pointed ends. The walls of fibres are generally lignified.
Sometimes their walls are so much thickened that the lumen or cell cavity is reduced very much or altogether
obliterated. The pits of fibres are always small, round or slit like and often oblique.
The pits on the walls can be numerous or few in number. The middle lamella is conspicuous in the fibres. In most
types of fibres, however, on maturation of cells the protoplast disappears and the permanent cell becomes dead
and empty. Very rarely the fibres retain protoplasts in them.
The fibres are abundantly found in several plants. They may occur in patches, in continuous bands and sometimes
singly among other cells. They provide strength and rigidity to the various organs of the plants to able them to
withstand various strains caused by outer agencies. The average length of fibres is 1-3 mm in angiosperms.

19. Cont..
• The fibres are divided into two large groups-xylem fibres and extraxylary
fibres.
• The xylem fibres evolve from the same meristematic tissues as the other
xylem cells and constitute an integral part of xylem.
• In other word, some of the continuous cylinders in monocotyledonous stems
arise in the ground tissue under the epidermis at variable distances.
• They are called cortical fibres.
• The fibres forming sheaths around the vascular bundles in the
monocotyledonous stems arise partly from the same procambium as the
vascular cells, partly from the ground tissue.
• The fibres present in the peripheral region of the vascular cylinder, often
close to the phloem, are called pericyclic fibres. The extraxylary fibres are
sometimes combines into a group known as bast fibres.

20. Sclereids
• The sclereids are broadly distributed in the plant body. They are usually not much
longer than they are broad, occurring singly or in groups.
• Generally these cells are isodiametric but some are elongated too. They are
commonly observed in the cortex and pith of gymnosperms and dicotyledons
arranged singly or in groups. In many species of plants, the sclereids occur in the
leaves.
• The leaf sclereids may be few to abundant. In certain leaves the mesophyll is
completely permeated by sclereids. Sclereids are also common in fruits and seeds.
In fruits they are disposed in the pulp singly or in groups (viz., Pyrus). The hardness
and strength of the seed coat is due to the presence of abundant sclareids.
• The secondary walls of the sclereids are typically lignified and vary in thickness. In
several sclerides the lumina are almost filled with massive wall deposits, and the
secondary wall shows prominent pits. Commonly the pits are simple and rarely
bordered pits may also exist.

21. Sclerieds

24. Complex tissue
• A complex plant tissue is made up of more than one type of cells.
There are two types of complex plant tissues, viz.
• Xylem and phloem.
• Xylem: Xylem is composed of four elements, viz.
Tracheids,
vessels,
xylem fibres and
xylem parenchyma.

25. Tracheids:
# These are elongated or tube-like cells. They have thick and lignified
walls and tapering ends.
# The tracheid cells are dead and protoplasm is absent.
# Tracheids and vessels are the main conducting elements in flowering
plants.

27. Vessel:
• These are long, cylindrical tube-like structures.
• These are made up of many cells which are called vessel members.
Each vessel member has lignified walls and a large central cavity.
• Protoplasm is absent in vessel cells.
• The vessel members are interconnected through perforations in their
common walls.
• The presence of vessels is a characteristic feature of angiosperms.

28. Xylem Fibres: The xylem fibres have highly thickened walls and
obliterated central lumens.
• Septa may be present or absent in xylem fibres.
Xylem Parenchyma:
• The xylem parenchyma is composed of living cells which are thin-
walled.
• The cell wall of xylem parenchyma is made up of cellulose. Xylem
parenchyma stores food in the form of starch or fat, and some other
substances like tannins.
• Parenchymatous cells facilitate the radial conduction of water in
plants.

29. Xylem vessel and trachids

30. • Primary xylem is of two types, viz. Protoxylem and metaxylem.
Protoxylem are the first formed primary xylem elements, while the
metaxylem are formed later.
• Endarch: The protoxylem lies towards the pith in stem and the
metaxylem lies towards the periphery. This type of primary xylem is
called endarch.
• Exarch: The protoxylem lies towards the periphery in roots and the
metaxylem lies towards the pith. This type of primary xylem is called
exarch.
• Transportation of water and minerals from roots to different plant
parts is the main function of xylem. Xylem also provides mechanical
strength.

31. Phloem

32. • Phloem:
• The phloem; in angiosperms; is composed of four elements, viz. Sieve
tube, companion cells, phloem parenchyma and phloem fibres.
• In case of gymnosperms, the phloem has albuminous cells and sieve
cells.
• Sieve tubes and companion cells are absent in the phloem in
gymnosperms.

33. Sieve Tube:
• The sieve tube elements are long, tube-like structures.
• They are arranged longitudinally.
• The end walls of sieve tubes are perforated to form sieve plates.
• A mature sieve element has a peripheral cytoplasm and a large
vacuole but no nucleus.
• The nucleus of the companion cell controls the function of sieve
element.

34. • Companion Cells:
• These are specialized parenchymatous cells.
• The companion cells are closely associated with sieve tube elements.
• There is a common pit field in the common longitudinal wall between
the sieve tube element and companion cell.
• These piths connect both of them.
• The companion cell helps in maintaining the pressure gradient in the
sieve tubes.

35. • Phloem Parenchyma:
• The cells of phloem parenchyma are elongated, tapering cylindrical
cells.
• The cells have dense cytoplasm and nucleus.
• Cell wall is composed of cellulose and has pits.
• Plasmodesmatal connections exist between the cells through these
pits.
• Phloem parenchyma stores food and other substances like resin,
latex and mucilage.
• Phloem parenchyma is usually absent in monocotyledonous

36. • Phloem Fibre:
• These are also called bast fibres and are made up of sclerenchyma.
• Phloem fibres are usually absent in primary phloem but present in
secondary phloem.
• The phloem fibres are much elongated, unbranched and have
pointed, needle-like apices.
• Phloem fibres of jute, flax and hemp are commercially used.

37. • The primary phloem which is first formed consists of narrow sieve
tubes and is called protophloem. The later formed phloem has bigger
sieve tubes and is called metaphloem.