Contemporary philippine arts from the regions_PPT_Module_12 [Autosaved] (1).pptx
THUJA.pptx
1. Thuja (Biota)
Thuja orientalis is a native of the eastern part of
Central Asia and is mainly distributed in North and West
China. The plant is cultivated as an ornamental all over the
world.
In India it is a common garden plant growing specially
well in the plains.
2. Habit and External Structure:-
1. Thuja is an evergreen tree reaching a
height of above 15 meters.
2. In gardens where it is cultivated, its constant
trimming for desired shape (bushy in
appearance) does not allow it to attain its
normal size and appearance.
3. Bailey (1948) has listed its 22 varieties
from North America based on size, shape,
manner of branching, colour and nature of
foliage leaves.
4. The bark of the tree is smooth, brownish
separating from older branches in the form
of papery scales.
3. 5. An undisturbed tree develops
horizontal lateral branches while In
cultivated plants both main and
lateral branches are vertical.
6. In young stages, plant has
vertical lateral branches, which
later on become horizontal.
7. Thus, this conifer is peculiar in
having different appearance of branches
at different ages.
8. A plant possesses a strongly
developed deep penetrating tap root
system with numerous branches.
4. 9. A young seedling shows occurrence of juvenile leaves.
10. In an adult plant there are present only foliage leaves.
11. The scale leaves are absent.
12. The foliage leaves are persistent functioning for several
years.
13. They are fused with the stem along one-third of its length.
14. The leaves are dark green, closely appressed, acute and
decussate.
15. Each leaf has on its abaxial (dorsal) surface a long median
groove.
16.The phyllotaxy is cyclic.
17. The shoots are flat. The leaves are arranged in flattened fan
shaped groupings with resin-glands, and oppositely grouped in 4
ranks.
5. ANATOMY
Young Stem :-
1. A transverse section of the young stem shows well
developed epidermis covered with cuticle.
2. a very wide cortex which contains photosynthetic
tissue towards the outer side while, the cells of
inner cortex are loose.
3. Vascular bundles are arranged in a ring.
4. In between vascular bundles medullary rays are
present.
5. Vascular bundles are conjoint, collateral, endrach and
open.
6. Pith is small while medullary rays are broad.
7. Resin canals are present in the cortex only.
6. Old Stem:-
1. Outer most layer is phellem.
2. Below it few layered phellogen present.
3. Inner to phelloderm i.e cork cambium is present which
add cells towards outer side forms phellogen.
4. Inner to phelloderm primary cortex is present and On
account of secondary growth it becomes very much
reduced which contains resin duct.
5. Next to cortex secondary phloem is present.
6. Inner to it cambium, Secondary growth occurs by the
activity of persistent primary cambium. which divide
and redivide add secondary phloem towards outer side
and secondary xylem towards inner side. Which forms
secondary wood.
7. In between secondary wood medullary rays are present.
8. Near the centre primary meta xylem and proto xylem is
present.
9. in an old stem the pith is completely destroyed.
7. 10. Xylem consists of tracheids only.
11. The protoxylem shows annular or
spiral thickening.
13. Phloem lacks companion cells.
14. The wood consists of tracheids
only, which shows pitted thickening.
15. The pits are uniseriate and confined
only to the radial wall.
16. The medullary rays are uniseriate
varying from 2-5 cells in their vertical
extent and are never associated with
resin canal.
8. T.S. Young Root:-
1. Outermost layer of the circular roots is thick-
walled epiblema with many root hair.
2. Epiblema is followed by many layers of
parenchymatous cortex.
3. Inner to the cortex is present a layer of
endodermis and many layers of pericycle.
4. Vascular bundles are radially arranged and
diarch to tetrarch with exarch protoxylem.
5. Protoxylem is bifurcated (Y-shaped) towards the
periphery, and in between each bifurcation is
present a resin cannal.
6. Phloem is present alternate to the protoxylem.
7. Pith is poorly-developed or absent.
9. T.S. of Old Root:
An old root shows pronounced secondary growth which shows -
1. On the outer side are present a few layers of cork, formed by the
meristematic activity of the cork cambium.
2. Cork cambium cuts secondary cortex towards inner side.
3. Many resin canals and stone cells are present in the secondary
cortex, the cells of which are separated with the intercellular
spaces.
4. Below the phloem patches develop cambium, which cuts
secondary phloem towards outer side and secondary xylem
towards inner side.
5. Crushed primary phloem is present outside the secondary
phloem
6. Many uniseriate medullary rays are present in the secondary
xylem.
7. Primary xylem is the same as in young roots, i.e., each group is
bifurcated (Y-shaped) and a resin canal is present in between the
bifurcation.
11. T.S. of Leaf:-
• The internal structure of Thuja leaf as seen in its cross section reveals its
xerophytic nature and can be differentiated into epidermis, hypodermis,
mesophyll and vascular cylinder regions.
• The epidermis is single layered with sunken stomata.
• The epidermal cells are thick walled and strongly cutinized.
• A single layered hypodermis with strongly lignified cells is present
below the epidermis.
• The mesophyll is differentiated into palisade and spongy parenchyma,
though this differentiation is not very sharp.
• Resin canals are present in the region of spongy parenchyma.
• In the centre of the lamina is present a single collateral vascular bundle
having protoxylem facing the ventral side and phloem on the dorsal side.
12. REPRODUCTION :-
The plants are heterosporous and monoecious i.e. both the types of cones
develop on the same plant. The male and female cones usually occur on separate
branch systems.
Female cone :-
• They are borne on the terminal branchlets and are little lower in position than
those bearing the male cones.
• Cones when young are covered by leaves.
• The branches bearing female cones are curved downwards.
• A mature cone measures 20-22 mm in length and 18 mm in diameter.
• Each female cone consists of 3 to 4 pairs of decussate, fleshy scales. The tip of
these scales is curved and spiny.
• Each scale is formed by the fusion of a bract and the so-called ovuliferous scales.
• The upper most pair of scales is usually sterile, while others bear 1 to 3
orthotropous, wingless ovules near the base on its ventral side.
• According to Martin (1950) only two pairs of scales of a female cone are fertile
and that two ovules are present on each of the lower fertile scales and one ovule
on each of the upper fertile scale. As such according to her there are six
ovules per cone.
• At the time of pollination the tip of each scale becomes curved on its. back, the
cone emerges out and exposes the ovules
13. Megasporangium(Ovule) and Megasporogenesis: -
• Each ovule consists of a massive nucellus covered by
integument which in early stages is 3-4 cells thick.
• At the tip region the thickness becomes of one layer.
• The integument is free from the nucellus in its upper part and
forms a micropyle.
• Nucellus contains one or two primary, sporogenous cells at
the level where the integument is attached to the nucellus.
• The cells of nucellus present above the sporogenous cells are
arranged in regular rows.
• The primary sporogenous cells by meiotic division form the
sporogenous tissue.
• This tissue increases considerably and a single megaspore
mother cell is differentiated in the centre of sporogenous
tissue.
• The megaspore mother cell undergoes reduction division
and forms a straight or slightly curved row of 3 cells.
• The lower two cells are megaspores, while the uppermost is
an undivided dyad cell, Of the two megaspores only chalazal
megaspore is functional,
14. Male Cone :-
• The male cones are born on the ultimate branchlets.
• When young they are completely covered by leaves.
• With the growth of male cone due to the elongation of the basal part
of the cone axis they emerge out from the leaves.
• A fully developed male cone measures about 2-3 mm in diameter
and bears 4 to 6 pairs of microsporophylls, arranged in a decussate
manner.
• Young cones at the time of emergence are, yellowish green in colour
but hen mature they become pale yellow.
• After shedding the pollen the cones become brownish in colour, dry up
and fall-off from the plant.
• Each microsporophyll at maturity is a small, rounded, shortly stalked, leaf
like structure .
• It is slightly broader at the base, convex on its dorsal surface and has
an inwardly curved margin.
• Near the base of each microsporophyll develop 3-5 mictosporangia on
its dorsal surface.
• In a mature male cone the microsporophylls get separated from each
other and thus the microsporangia are exposed.
15. Microsporangium and Microsporogenesis :-
• The development of rnicrosporangium is of eusporangiate type.
• The hypodermal archesporial cells develop on the dorsal side
towards the base of microsporophyll.
• A periclinal division in the archesporial cells forms primary
parietal layer and primary sporogenous layer.
• The primary parietal layer divides to form two layers.
• The layer which is in immediate contact with sporogenous
tissue becomes densely cytoplasmic and forms tapetum.
• The microspore mother cells undergo reduction division to form
tetrad of microspores.
• The tetrad formation may be of either successive or simultaneous
type, i.e., a wall may or may not be formed between the two dyad
nuclei.
• Each microspore when fully formed becomes rounded, bears a
large nucleus and several starch grains.
• It has got two wall layers exine and intine.
• The exine remains thin, while the intine is considerably thicker.
