AOFP 2 Flashcards
Types of development of primary xylem
(On the basis of position of protoxylem):-
Centrifugal( endarch)
Protoxylem → Towards central
Metaxylem → Towards peripheral
E.g. Stem of angiosperms & gymnosperms
Centripetal( exarch)
Protoxylem → Towards peripheral
Metaxylem → Towards central
E.g. Roots (Exarch)
Centrifugal & Centripetal
Protoxylem is surrounded by
metaxylem
E.g. Rhizome of fern (underground
stem)
types of vascular bundles
CONJOINT VASCULAR
BUNDLES
(stem & leaf)
(Xylem and phloem
are present on the
same radius)
RADIAL VASCULAR
BUNDLES
(root)
(Xylem and phloem
are present separately
on different radius)
CONCENTRIC VASCULAR
BUNDLES
(stem of fern & some monocot)
(Either xylem surrounds
the phloem or phloem
surrounds the xylem,
always closed)
types of conjoiint vascular bundles
i)Conjoint, collateral
(Phloem is present towards the
periphery)
ii) Conjoint , bicollateral
(Phloem present on both side
of xylem, always open)
stem of cucurbitaceae
iii)
usually in root thr is radial arrangement of vascular bundles. in which oneis it conjoint collateral
Most of the roots (Dicot, monocot, gymnosperm, fern root).
exception: In radish, carrot, turnip and sugarbeet (Beet root)
roots, vascular bundles are conjoint, collateral.
explain monocot stem vascular bundle
Many, scattered, oval shaped. Each vascular
bundle is conjoint, collateral and closed and xylem is endarch.
*Each vascular bundle is surrounded by fibrous sclerenchymatous
bundle sheath.
Cavities-
1.Lysogenic - Spaces formed by
breakdown of cells.
2.Schizogenous - Spaces formed
by separation of cell wall.
Xylem: In metaxylem there occurs two large vessels while in
protoxylem there occurs one or two small vessels.
* Vessels are arranged in the form of V or Y.
* Water cavity present within vascular bundles which is
schizolysigenous in origin.
Phloem: Phloem parenchyma is absent.
difference between monocot and dicot leaf
dicot leaf is dorsiventral or bifacial. It is also hypostomatic meaning it has more stomata on abaxial surface
monocot leaf is isobilateral or equifacial. It is also amphistomatic meaning there is equal stomata on abaxial and adaxial surface.
what is secondary growth
The growth of the roots and stems in length with the help of apical
meristem is called the primary growth.
Apart from primary growth most dicotyledonous plants exhibit an
increase in girth. This increase is called the secondary growth.
*The tissues involved in secondary growth are the two lateral
meristems: vascular cambium and cork cambium.
describe secondary growth
*Increase in the circumference or girth of the plant organs.
*Takes place in roots and stem of Dicotyledons & Gymnosperms.
*Not found in leaves and monocots (root &stem).
*In monocotyledons, secondary growth is absent.
*These plants show abnormal secondary growth. Exceptions – Date Palm,
Yucca, Dracaena).
explain 2° growth in stelar region ( stem)
*A cambium present inside the vascular bundle is called Intrafascicular
cambium (Primary lateral meristem).
*Some cells of medullary rays become meristematic to form Interfascicular
cambium (secondary lateral meristem).
*Both are collectively known as Vascular Cambium (formed in the form of a
complete ring).
* The vascular cambium ring is particly primary and partly secondary in origin. The cells of medullary rays are secondary while intrafascicular cambium is primary.
*Two types of cells are found in the ring of this vascular cambium –
1.Fusiform initials
2.Ray initials
explain the activity of fusiform intials
*Long pointed ends & more in number.
*Continuous periclinal( parallel to plane) divisions takes place in fusiform initials.
*Towards the periphery(towards pericycle) – 2° Phloem or Bast.
*Towards the centre – 2° Xylem or Wood.
*By the pressure of secondary xylem, all the primary tissues- such as primary
xylem, pith are pushed towards the centre.
*The primary xylem however remains more or less intact in or around the
centre. The primary and secondary phloem of the earlier get gradually
crushed due to the continued formation and accumulation of secondary
xylem.
Secondary xylem is formed 8 – 10 times more as compared to
secondary phloem.
what is the activity of ray initials
*Spherical / rounded or oval in shape.
- less in number
*Due to periclinal divisions, ray initials form parenchymatous cells (Secondary
medullary rays).
*Vascular rays or Sec. medullary rays which passes through the secondary
xylem and secondary phloem in the radial direction.
*They conduct water and food in radial direction.
what are annual rings
Annual rings are formed due to unequal activity of vascular cambium.
*Activity of vascular cambium is affected by physiological and
environmental factors.
*In temperate regions, the climatic conditions are not uniform through the
year.
two types of wood
Spring wood or Early wood
The activity of
cambium is faster.
Produces large number of xylem elements.
Xylem vessels/
trachieds have wider lumen.
Wood is lighter in colour and has lower density
Autumn wood or Late wood
Activity of
cambium is
slower
Produces fewer
xylem elements.
Xylem vessels/
trachieds have
narrow lumen.
Wood is darker in colour and has a higher density.
describe annual rings
*A ring of autumn wood and a ring of spring wood are collectively known as
Annual ring (gives the idea of the age of the tree).
*The study of determination of age of a tree by counting annual ring is called
Dendrochronology.
*Annual rings are counted from the base of stem because basal part has
maximum annual rings.
*More clear annual rings are formed in that regions where climatic
variations are sharp (E.g.- Temperate plants).
*Distinct annual rings are not formed in tropical plants. Distinct / clear
annual rings are not formed in India except Himalayan regions (Shimla,
Nainital etc.).
*In seashore regions / coastal regions and deserts annual rings are less
distinct.
differentiate between alburnum and Duramen
Sap Wood (Alburnum)
Living part of the wood.
It is situated on
the outer side of
wood
It is less in coloured
Very soft in nature
Tyloses are absent
It is not durable and not resistant to microorganisms
Heart Wood (Duramen)
Dead part of the wood.
It is situated in
the centre part of wood
It is dark in coloured
Hard in nature
Tyloses are present
It is more durable and resists
microorganisms