1. The document discusses various types of anomalous structures that can occur in dicot stems, including the presence of medullary or cortical bundles, absence of vessels, abnormal cambium activity, presence of phloem bundles or scattered vascular bundles, and presence of interxylary or included phloem. 2. It provides examples of these anomalies in specific plants like Boerhaavia, Achyranthus, Bignonia, Amaranthus, Mirabilis, and Leptadenia. In these plants, the anomalous structures arise due to abnormal primary structure, abnormal secondary growth, or abnormal cambium behavior. 3. The secondary growth in some plants like Boerhaavia, Achyran

1. Anomalous structure in dicotyledonous
stem
DR. VISHNUPRIYA SHARMA
DEPARTMENT OF BOTANY
M.Sc. Sem –II, Paper BOT202
Anatomy and Reproductive Biology of Angiosperms

2. Anomalous secondary features in dicot stems
The dicotyledons stems in most of cases have the normal structure in which a ring of
collateral vascular bundles are found. At the time of secondary growth, inner and
interfascicular cambium cut off xylem towards the inner side and phloem towards the outer
side .However in a number of plants abnormal conditions are met with Abnormality is due to
the two causes :
(1) In some the primary structure itself is abnormal.
(2) The primary structure is normal but secondary growth is abnormal
The anomalous structures in dicot stems may be due to :
1. The presence of medullary or cortical bundles. In Boerhaavia there are two rings of
medullary bundles-inner of two, rather, big bundles and in outer of generally six or more
vascular bundles. In Achyranthes there are only two medullary bundles, which in internodal
part, point their proto xylem towards each other. In Mirabilis, Bouganvilea and other
members of the family Nyctaginaceae medullary bundles are present. In Chenopodium the
medullar bundles remain embedded in parenchymatous pith. Here they are said to be
leaftraces
2. Due to the presence of cortical bundles. Some times a ring of vascular bundles is found in
cortical region. These bundles may be referred as "cortical bundles" or they may be
interpreted as leaf traces. The presence of such type of bundles has been studied in many
families e.g. Bignonaceae,Casuarinaceae, (Casuarina) Cucurbitaceae, Proteaceae, Oleaceae
and many others.

3. (2)Due to the absence of vessels. Though the presence of of vessels in
angiosperm s is normal feature but some genera like Ballium, Drimays,
Exospermum, Wintera, Zygogynum, Trochodendron Tetracentron do not
posses vessels.
(3) Due to the abnormal behaviour of normal cambium: Sometimes when
the normal cambium starts cutting cells at several places in irregular
fashion and form at some places much larger proportions of xylem than of
Poem, and at other places more phloem than xylem and a rigid and
furrowed ylinder is produced. They may be simple type e.g. Bignoniaceous
species or a complex one as in Bignonia.
(4) Due to presence of phloem bundles. Sometimes only phloem bundles
are found developed in between outer collateral bundlese.g. Cuscuta.
(5) Due to presence of scattered vascular bundles in dicots e.g.Peperomla,
Piper, Thalictrum, Nymphaea, Papever originale and. Elas-tostemma
sessiliS.
(6) Due to presence to Interxylary or included phloem. In some plants like
Combretum, Salvadora, Leptadenia etc. the interxylary phloem occurs

4. Abnormal Behaviour of Secondary cambium
A. Normal cambium with abnormal activity eg Bignonia, Aristolochia
B. Abnormal cambium with abnormal activity eg Amaranthus ,Achyranthus ,Boerhaavia
Mrabilis, Chenopodium
Abnormal secondary growth in Bignonia Stem
Normal cambium with abnormal activity
The transverse section of young Bignonia stem is like that of typical dicot. Stem, At the time of
secondary growth the Inter fascicular cambium develop in the normal way forming a complete
ring of cambium. Now the cambium ring forms xylem towards inner side and phloem towards
outside in the normal way. The amount of secondary xylem formed is much more as compared
to the amount of secondary phloem formed.
The cambium ring after performing, for a short time, its normal functions, begins at certain point
to give off internally only a very small quantity of xylem and external a large amount of phloem.
As a result of this ,deep wedges of irregularly widening phloem project into the outer xylem. In
this way normal cambium shows abnormality as a result of which 4, 8 or more wedges are
formed. The formation of cork cambium and cork takes places in the normal way.
Abnormal cambium' with abnormal activity-In this case the normal cambium ceases its
functioning after very short period and then an abnormal type of cambium development takes
place from cortex or pericycle and behaves in an abnormal way, as for e.g., in Amaranthus,
Achyranthus Boerhavia, Bougonvilla, Chenopodium

7. Abnormal secondary growth in Amaranthus stem
The transverse section of young Amaranthus stem is some what circular in outline with a single
layered epidermis, few layered endodermis and parenchyma. There is also present a single
layered collenchyma and few layered pericycle and a central pith. In the central region their
remain present two collateral ,open and conjoint vascular bundles known as medullary vascular
bundles. In this stem at the time of secondary growth
(a) The normal cambium is inactive.
b) The cambium develops from the pericycle.
(c) The activity of this cambium is abnormal.
So at the time of secondary growth any layer of the pericycle becomes meristematie and forms
pericyclic cambium. The cambium starts to cut xylem on the inner side in patches alternating
with pårenchyma patches and phloem towards outer side just above the xylem patches and
phloem towards outer side just above the xylem patches and parenchyma at rest of places. The
previously formed parenchyma get shifted upward phloem than form secondary cortex. Now at
this stage the vascular bundles so formed from a structure like that of original collateral, open
and conjoint vascular bundles Now the activity of this cambium cases and becomes
functionless. After it another cambium development take place from secondary cortex. Its
activity is just similar to the of pericyclic cambium as a result of which one more ring of vascular
bundle formed outside the first ring of vascular bundles. After this, cambium so becomes
functionless and third cambium develops from the secondary cortex which also shows the
similar type of activity and as result of which third ring of vascular, bundles formation takes
place and in this large number of rings of vascular bundles formed formation takes place. The
cambium formation takes place in the normal way. In this way Amaranthus stem shows
abnormal secondary growth, in which abnormal cambium shows abnormal activity.

10. Abnormal Secondary growth in Boerhaavia Stem
Young stem of Boerhaavia (family Nyctaginaceae) structure is just like a typical
dicotyledonous stem with the only difference that it has three rings of vascular
bundles. In the centre there are present two big sized vascular bundles forming first
ring of vascular bundle and known as medullary vascular bundles. Surrounding the
medullary bundles there remain present a ring o f6 to 20 normal sized vascular
bundles forming the second ring of vascular. Outer the second ring of vascular bundles
arranged in a ring and contain 15 to 20 vascular bundles.
At the time of secondary growth the cambium of first and second ring of vascular
bundles remain inactive and show a very little activity within the vascular bundles
only. The cambium of the third ring of vascular bundle remain active and by the
development of interfascicular cambium completes the cambium ring. Now this
normal cambium ring shows abnormal activity.
In the regions of vascular bundles the cambium forms xylem towards innerside and
rest of places it cuts sclerenchyma, while towards outerside it forms simple
parenchyma only for a short period and then cambium begins to cut the phloem on
the outer side just above the xylem which alternates with the sclerenchyma and in
this way the previously formed parenchyma gets pushed up ,and the cambium ceases
its activity. After some time the formation of cambium takes place from the
parenchyma. Thus in Boerhaavia stem the secondary growth takes place by the
abnormal cambium with abnormal activity.

13. Abnormal secondary growth in Achyranthus stem-
In this case the anomalous
growth in thickening takes
place by the development of
the successive rings of the
collatral bundles from one ring
of secondary meristematic
tissue in the pericyclic region.
The secondary arch of rings or
secondary meristematic tissue
in the pericycle give rise to
collateral vascular bundles
successively. The conjunctive
tissue between bundles may
be consisted of parenchyma in
some species and in others of
lignified or unlignified
parenchyma.

15. Mirabilis Stem (family Nyctanginacéne)
The transverse section shows a outer most layer epidermis which
is covered with a thin cuticle. Below epidermis there is a broad
cortical region consisting of collenchyma. parenchyma and
endodermis. Below endodermis few layer of parenchymatous cell
represent pericycle, Below the pericycle the phloem is present.
The xylem is represented by a continuous cylinder of xylem
parenchyma and xylem vessels.
The central portión of the stem consist of thin walled rounded oval
shaped or polygonal parenchymatous cells, called ground tissue.
The abnormal secondary thickening occures in the form of a
succession of rings of vascular bundles. The secondary bundles
exhibit a concentric or irregular arrangement becoming embedded
in parenchymatous tissue.

17. Topographical sketch of Mirabilis stem after secondary growth

18. TS of Mirabilis stem after secondary growth

19. Abnormal secondary growth in Leptadenia stem:
The T.S. of stem of Leptadenia (family Asclepiadaceae) shows an outer most layer
epidermis, consist of single row of compact cells and is covered with a thick cuticle.
Below epidermis, hypodermis is present which consist of one or two layer of thin walled
parenchymatous cells. Below it few layers of chloroplasts and there cells known as
chlorenchyma. Below it endodermis is present which consists of barrel shaped and
compact cells. Below the endodermis, a broad pericycle is present. This zone consists of
thin walled parenchymatous cells interrupted by unlignified patches of sclerenchyma.
Below it the phloem is present. The secondary phloem is conspicuous consisting of
sieve tubes, companion cells and phloem parenchyma. The primary phloem is also seen
at certain places in crushed froms. Below secondary phloem cambial zone is present.
The cambium consists of thin walled rectangular cells arranged in radial rows. Below
cambium the xylem is present which is represented by both primary and secondary
xylem vessels and vascular tracheids. The primary xylem is confined towards pith
region. The secondary xylem which is continuous remain interrupted by the strands of
interxylary or included phloem which develop centripetally. In the central region a less
develop parenchymatous pith also remain present. The latex tubes are also found
among the parenchymatous tissue.
The stem of Leptadenia shows anomalous structure due to the presence of included
phloem in secondary xylem and xerophytic characters due to the presence of (i) a thick
cuticle over epidermis. (ii) photosynthesis tissue is present in stem, (iii) well developed
sclerenchymatous pericycle is present, (iv) the latex tubes are present and (v) the
mechanical tissue is well developed