Anatomy

1. Mr.D.L.Gavande
Assistant Professor
Department of Botany
Shri Shivaji Science and Arts College, Chikhli.

2. Anatomy of Dicotyledonous Roots
I. Cicer- Root:
 It is circular in outline and reveals following tissues from outside with-in:
 Epiblema:
 It is the outermost layer consisting of many thin-walled cells.
 From some of its cells arise unicellular hair.
 Cuticle is absent.
 Cortex:
 It is very large, parenchymatous and well- developed occupying the large part of the section.
 In this region there are present many intercellular spaces.
 Cortical cells are filled with starch grains.
 In older roots, few-layered exodermis, consisting of thin-walled compact cells, is present just
below the epiblema.
 Endodermis is the ring like innermost layer of cortex made up of barrel-shaped cells.
 Casparian strips are present in the endodermal cells.
 Some of the endodermal cells, particularly those opposite to the protoxylem, are thin-walled
and have been termed as passage cells.

3.  Pericycle:
 Single-layered, ring-like pericycle is present close to the endodermis on its inner side.
 It is also a compact layer of thin-walled cells.
 Vascular Bundles:
 The vascular bundles are 2 to 6 and radial, i.e., xylem and phloem present on different radii
alternating with each other.
 Xylem and phloem patches are equal in number.
 Xylem consists of protoxylem and metaxylem.
 Protoxylem is exarch and consists of small annular and spiral vessels.
 Metaxylem strands are big, present towards the centre and are made up of large reticulate and
pitted vessels.
 In some cases the metaxylem meet in the centre and thus obliterate the pith.
 Phloem is made up of sieve tubes, companion cells and phloem parenchyma.
 In mature roots, cambium also appears cutting the secondary structures.
 The parenchymatous cells in between xylem and phloem strands form conjunctive tissue.
 Pith:
 It is very small, parenchymatous and without any intercellular spaces. It gets reduced after the
formation of secondary structures.

5. II. Tinospora-Root:
 T.S. appears circular in outline and reveals following tissues (Fig. 171)
from outside with-in:
 Periderm:
 It consists of cork, cork cambium and secondary cortex which are also
termed as phellem, phellogen and phelloderm, respectively.
 Cork is the outermost region of the section, consisting of dead cells which
are rectangular in shape. It is few to many cells deep.
 Cork cambium is meristematic in nature and cuts cork on the outer side and
secondary cortex towards inner side.
 Secondary cortex consists of thin-walled, parenchymatous, rounded or oval
cells leaving many intercellular spaces. Cells are filled with many plastids.
 Endodermis is present in the form of a single layer in young stages but at
maturity it is not visible due to the formation of periderm.

6.  Pericycle:
 Single-layered pericycle, consisting of barrel-shaped cells, is clearly observed in young roots.
 Vascular System:
 Vascular bundles are radial, exarch and show the secondary growth due to the presence of cambium.
 Vascular tissue remains divided into many smaller groups due to the presence of broad medullary rays.
 Vascular tissue consists of primary phloem, secondary phloem, cambium, secondary xylem, primary xylem
and medullary rays.
 Primary phloem is crushed and is present alternate with primary xylem groups.
 Secondary phloem cambium developed below the primary phloem. Phloem consists of sieve tubes, phloem
parenchyma and companion cells.
 Cambium is one to many cells-thick, wavy and present in the form of a complete ring.
 Secondary xylem is well-developed and consists of tracheids, xylem parenchyma and large vessels.
 Primary xylem groups are centrally located and face their groups towards periphery.
 Medullary rays are parenchymatous, multiseriate and separate the vascular tissue in small groups.
 Pith:
 It is ill-developed.
 Aerial Characters:
 Presence of lenticels.
 Well-developed cork.
 Chlorenchymatous secondary cortex.
 Absence of root hair.

8. III. Ficus-Root:
 It is circular in outline and reveals following tissues from outside with-in:
 Periderm:
 It is composed of cork, cork cambium and secondary cortex.
 Cork is well-developed and its 6 to 8 or more layers are present.
 The cells are rounded, irregular or rectangular in shape and may be filled with
tannin.
 Cork cambium or phellogen is well-developed and meristematic in function.
 Secondary cortex or phelloderm is parenchymatous and the cells contain chlorophyll
in young stages. The cells are rounded with many intercellular spaces in between.
 Root hair are absent.
 Endodermis is well-developed, single-layered and present in the young root but it
gets crushed due to the secondary growth in later stages.
 Pericycles:
 Crushed due to secondary growth.

9.  Vascular Tissue:
 It is composed of crushed primary phloem, well- developed secondary phloem, cambium, secondary xylem
and primary xylem.
 Primary phloem is radial to primary xylem and present in the form of crushed patches. The number of the
patches are as many as the number of xylem groups.
 Secondary phloem ring is situated inner to the primary phloem. It consists of sieve tubes, companion cells
and phloem parenchyma.
 Cambium is present in the form of a continuous ring. But opposite to protoxylem, it is consumed in the
production of medullary rays.
 Secondary xylem is well-developed and consists of large vessels, tracheids and xylem parenchyma.
 Primary xylem bundles are centrally located, two to six or rarely more in number and facing their
protoxylem towards the periphery, i.e., it is exarch.
 Pith:
 It is very small, parenchymatous and present in the centre.
 Aerial Characters:
 Root hair are absent.
 Well-developed, rough-type of cork.
 Presence of lenticels.
 Secondary parenchyma contains chloroplast.
 Cuticle is present in young roots.

11. Anatomy of Monocot Root
oZea mays-Root:
 It is circular in outline and reveals the following tissues from outside with-in:
 Epiblema:
 Single-layered epiblema consists of barrel- shaped or rounded cells.
 From some cells arise unicellular hair.
 Cortex:
 It is well-developed, several cells deep and parenchymatous.
 The cells are thin-walled, rounded in shape and leave many intercellular spaces.
 Just below the epiblema are present 2 to 6 layers of collenchyma in old roots. This represents
exodermis.
 Remaining part of the cortex is parenchymatous.
 Endodermis is the innermost layer of cortex. It consists of many compactly arranged, barrel-
shaped cells.
 Casparian strips are present on the radial and transverse walls of the endodermal cells.
 Thin-walled endodermal cells are known as passage cells. They lie opposite to protoxylem.
 Pericycle:
 Single-layered pericycle consists of thin-walled cells and present inner to the endodermis.

12.  Vascular Tissue:
 It is composed of alternating strands of phloem and xylem.
 Vascular bundles are radial, exarch and polyarch. Cambium is absent.
 Xylem consists of vessels, tracheids and xylem parenchyma.
 Protoxylem elements are towards the outer side, i.e., exarch, small in diameter and
their walls have thickenings.
 Metaxylem vessels face towards the centre and have larger diameter. Innermost
metaxylem vessel is very large and spherical or oval.
 Phloem consists of sieve tubes, companion cells and phloem parenchyma. It exhibits
exarch condition with its protophloem towards the periphery and metaphloem
towards the centre.
 Thick-walled, sclerenchymatous conjunctive tissue is present in between the
vascular bundles.
 Pith:
 It is well-developed and parenchymatous.
 The cells are round in shape and leave many intercellular spaces.

14. Introduction to Secondary Growth
 The roots of gymnosperms and most
dicotyledonous undergo secondary growth.
 Most of the dicotyledonous roots show
secondary growth in thickness, similar to
that of dicotyledonous stems.
 However, the roots of extant vascular
cryptogams and most monocotyledons do
not show any secondary growth; they
remain entirely primary throughout their
life.
 The secondary tissues developed in the
dicotyledonous roots are fundamentally
quite similar to that of dicotyledonous
stems, but the process initiates in some
different manner. Certain dicotyledonous
roots do not show secondary growth.
 The secondary vascular tissues originate as
a result of the cambial activity.
 The phellogen gives rise to the periderm.

15.  Formation of Cambium and
Development of Secondary Tissues:
 The dicotyledonous roots posses a limited number
of radial vascular bundles with exarch xylem.
 Normally the pith is very little or altogether
absent.
 On the initiation of secondary growth, a few
parenchyma cells beneath each group of phloem
become meristematic and thus as many cambial
strips are formed as the number of phloem
groups.
 The cambial cells divide tangentially again and
again and produce secondary tissues.
 Thereafter some of the cells of single layered
pericycle become meristematic lying against the
protoxylem groups, which divide and form a few
layers of cells.
 The first formed cambium now extends towards
both of its edges and reaches the inner most
derivatives of the pericycle, thus giving rise to a
complete ring of cambium.

16.  The cambium ring is wavy in
outline, as it passes internal to
phloem and external to xylem
groups.
 The cambial cells produce more
xylem elements than phloem.
 The first formed cambium
produces secondary xylem much
earlier, and the wavy cambium
ring ultimately becomes circular.
 Now whole of the cambium ring
becomes actively meristematic,
and behaves in the similar way as
in the stem, giving rise to
secondary xylem on its inner side
and secondary phloem towards
outside.

17.  The secondary vascular tissues form a
continuous cylinder and usually the
primary xylem gets embedded in it.
 At this stage distinction can be made
only by exarch primary xylem located
in the centre.
 The primary phloem elements are
generally seen in crushed condition.
 The cambial cells that originate from
the pericycle lying against the groups
of protoxylem function as ray initials
and produce broad vascular rays.
 These rays are traversed in the xylem
and phloem through cambium; this is
characteristic feature of the roots.
 Normally, such rays are called
medullary rays.