Agathis, a member of the Araucariaceae family, is a tall evergreen tree characterized by a columnar trunk and spirally arranged leaves that can last 15 to 20 years. Its reproductive structures include dioecious male cones that are cylindrical and female cones that are large and sub-globose, consisting of spirally arranged megasporophylls with fused ovuliferous scales. The embryogenic process results in a thick seed coat with 2 to 4 cotyledons and the seeds undergo epigeal germination.

1. AGATHIS
ARAUCARIACEAE
MORPHOLOGY
• Tall trees – 40 metres
• Evergreen, columnar trunk with whorled horrizontal branches.
• Leaves spirally arranged on main stem & opposite on lateral
shoots.
• Reddish when young & dark green when old.
• Long, petiolate, thick glabrous, broad, ovate-lanceolate with
parallel venation.
• Cushion like scars left on leaf fall.
• Leaves remain for 15 to 20 years.
• Root – typical tap root with developed branches.

3. ANATOMY
Root – Epidermis – single layered.
Cortex – parenchymatous, 6-7 layered.
Endodermis – single layered – tanniferous.
Pericycle – 5 to 7 layered, has resin ducts in rings.
Stele – diarch condition.
Sec. Growth as usual with uniseriate rings.
Stem – Thin cuticle & epidermis.
Many layered parenchymatous cortex – 2 zones.
Outer zone – 3 to 4 layers small tanniferous cells.
Inner zone – large cells, some with tannin.
2 rings of resin ducts – one below eidermis.
Other associated with vas. bndls. – outside phloem.
Vas.bndls. Collateral & open.
Leaf traces in pairs.
Sec. thickening – bordered pits & uniseriate rays & sclerids

4. Leaf – dorsiventral.
Upper epidermis – rectangular cells, highly
cuticularised.
Hypodermis – stone cells seen.
Sub-epidermal layer – with tannin cells.
Palisade – elongated, compactly arranged.
Inner to spongy another layer of palisade
seen.
Through out mesophyll - sclerids present.
Stomata on both upper & lower epidermis.
Vas.bndls numerous, alternate with resin ducts.
Bundle sheath – sclerenchymatous fibres.
Xylem & phloem as usual.

5. REPRODUCTION
Plants are dioecious.
Male cones cylindrical, solitary or in clusters on the
lower branches of trees.
Cones – erect, subsessile & axillary.
Microsporophylls – spirally arranged around axis.
Each with small stalk, peltate head & 5 to 15
microsporangia in 2 rows.
Long cone axis elongates when sporangia mature.
By a longitudinal slit – sporangia dehise in April- March.
Microsprorogenesis same as in others – innermost wall
layer forms tapetum.

7. • Female cones large, solitary, stalked, sub-
globose – upper part of trees. Central axis –
megasporophylls spirally arranged – each
broader than long – thick in the centre with 2
membraneous lateral extensions & a short
upturned tip – a single ovule develops on the
adaxial surface of megasporophyll & is fused
to sporophyll only at its base – ovuliferous
scale & bract scale completely fused.

8. • Ovule development same as in others –
unitegmic, orthotropus – group of archesporial
cells – one of them as megaspore mother cell –
R/D – triad of megaspores – lowermost one
functional.

9. • Functional Megaspore
• Nuclear division
• Upto 500 nuclei
• Cellularization occurs
• Archegonial initial – large central cell & small neck
initial
• Neck initial – 12 wedge shaped cells in one tier
• Central nucleus – Egg nucleus & ventral canal nucleus
• Egg nucleus surrounds cytoplasm – Egg cell

10. • POLLINATION – by wind
• FERTILIZATION – as usual.
• EMBRYOGENY
• Zygote nucleus
• Nuclear divisions
• 64 proembryonal nuclei
• Free nuclear proembryo
• Nuclei arranged in 3 groups
• Upper – single row of large radially elongated nuclei
• Middle – few round nuclei of 2 rows
• Lower – elongated nuclei - fewer in number

11. • Wall formation
• Suspensor develops – pushes embryo deep inside
• Only simple polyembryony
• Cotyledons – 2 to 4 in number
• Seed coat – thick – outer 4 to 5 layers & inner 5 to 6 layers
• Seed germination epigeal
•

12. AGATHIS