Thuja is an evergreen tree native to Central Asia and China, commonly cultivated as an ornamental plant worldwide. The document details its anatomy, including variations in leaf structure, root and stem anatomy, and reproductive characteristics of male and female cones, highlighting its unique features at different growth stages. Additionally, it discusses the plant's life cycle and the processes of megasporogenesis and microsporogenesis.

2. Classification
Class: Coniferopsida
Order: Coniferales
Family: Cupressaceae
Genus: Thuja

3. Distribution
• 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.

5. Habit and external structure
• Thuja is an evergreen tree reaching a height of above 12
meters.
• Cultivated in garden, its constant trimming for desired
shape (bushy appearance) does not allow it to attain its
normal size and appearance.
• Bailey (1948) has listed its 22 varieties from North America
based on size, shape, manner of branching, colour and
nature of foliage leaves.
• The bark of the tree is smooth, brownish separating from
older branches in the form of papery scales.

6. • An undisturbed tree develops horizontal-
lateral branches while in cultivated plants-
both main and lateral branches are vertical.
• In young stage, plant has vertical lateral
branches, which later become horizontal.
• Thus, this conifer is peculiar and having
different appearance of branches at different
ages.
• A plant possesses a strongly developed deep
penetrating tap root system with numerous
branches.

7. • A young seedling shows occurrence of Juvenile leaves.
• In an adult plant there are present only foliage leaves.
• The scale leaves are absent.
• The foliage leaves are persistent functioning for several years.
• They are fused with the stem along one- third of its length.
• The leaves are dark green, closely appressed, acute and decussate.
• Each leaf has on its abaxial (dorsal) surface a long median groove.
• The phyllotaxy is cyclic.
• The shoots are flat. The leaves are arranged in flattened fan shaped
groupings with resin- glands, and oppositely grouped in 4 ranks.

8. Anatomy of young stem
• A transverse section of the young stem shows well developed epidermis covered with
cuticle.
• A very wide cortex which contains photosynthetic tissue towards the outer side while, the
cells of inner cortex are loose.
• Vascular bundles are arranged in a ring.
• In between vascular bundles medullary rays are present.
• Vascular bundles are conjoint, collateral, endarch and open.
• Pith is small while medullary rays are broad.
• Resin canals are present in cortex only

9. Anatomy of young stem

10. Anatomy of old stem
• Outer most layer is phellem.
• Below it few layered phellogen present.
• Inner phelloderm i. e cork cambium is
present which add cells towards outer
side forms phellogen.
• Inner to phelloderm primary cortex is
present and on account of secondary
growth it becomes very much reduced
which contains resin duct.

11. • Next to cortex secondary phloem is present.
• 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.
• In between secondary wood medullary rays are
present.
• Near the centre primary meta xylem and
protoxylem is present.
• In an old stem pith is completely destroyed.

12. • Xylem consists of tracheids only.
• The protoxylem shows annular and spiral
thickening.
• Phloem lacks companion cells.
• The wood consists of tracheids only, which
shows pitted thickening.
• the pits are uniseriate and confined only
to the radial wall.
• The medullary rays are uniseriate varying
from 2-5 cells in their vertical extent and
are never associated with resin canal

13. Anatomy of young root
• Outermost layer Of the circular roots is thick walled
epiblema with many root hair.
• Epiblema is followed by many layers of parenchymatous
cortex.
• Inner to the cortex is present a layer of endodermis and
many layers of pericycle.
• Vascular bundles are radially arranged and diarch to
tetrarch with exarch protoxylem.
• Protoxylem is bifurcated (Y-shaped) towards the periphery,
and in between each bifurcation is present a resin canal.
• Phloem is present alternate to the protoxylem.
• Pith is poorly-developed or absent.

14. Anatomy of old root
An Old root shows pronounced secondary growth which shows
• On the outer side are present a few layers Of cork, formed by the meristematic activity Of the
cork cambium.
• Cork cambium cuts secondary cortex towards inner side.
• Many resin canals and stone cells are present in the secondary cortex, the cells of which are
separated with the intercellular spaces.
• Below the phloem patches develop cambium, which cuts secondary phloem towards outer
side and secondary xylem towards inner side.
• Crushed primary phloem is present outside the secondary phloem
• Many uniseriate medullary rays are present in the secondary xylem.
• 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.

15. Anatomy of old root

16. Anatomy 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.

17. Anatomy of leaf

18. 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 ovuliferous scales.
• The upper most pair of scales is usually sterile, while others bear 1 t03 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

19. Female cone

20. 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,

21. 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.

22. Male cone

23. Microsporangium and Microsporogenesis
The development of microsporangium 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.

24. Life cycle