GINKGO...................................pptx

Ginkgo

1. GINKGO MERIN ALICE GEORGE

2. CLASS: CONIFEROPSIDA ORDER: CONIFERALES FAMILY: GINKOACEAE

3. The maidenhair tree is one of the oldest living tree species in the world. Known as a ‘living fossil’, it is the sole survivor of an ancient group of trees that outlived the dinosaurs.  Though endangered in the wild because of deforestation, the maidenhair tree is cultivated throughout the world and prized for the medicinal properties of its leaves.

4. It has fan-shaped, greenish-yellow leaves that have two or more distinct lobes. In autumn, the leaves of the maidenhair tree turn golden and fall to the ground. Whilst male trees have pollen-producing floral spikes, fertilized female trees bear round, fleshy, yellowish fruits that contain a large seed and have an unpleasant scent. It takes 20—35 years for maidenhair trees to reach maturity and start bearing fruits.

5. MORPHOLOGY An attractive tree – pyramidal shape. Trees 30 m tall, fan-shaped deciduous leaves. Fruits – orange in colour – resemble apricot in size & colour. Female tree – fruits emit offensive odour – due to lactic acid – hence only male trees are preferred in gardens. Male & female trees identical – takes 20 years to flower – seed propagation not common – since female plants are not preferred. Propagation mainly by layering, grafting and cuttings. Stem – 2 types of branches – shoot dimorphism – long shoots & dwarf shoots.

6. Long shoots – 1 meter long – unlimited growth – elongate rapidly – grow fast – bear scattered leaves. Dwarf shoots – spur shoots – limited growth – slow growth – cluster of leaves at apex – arise from axils of leaves on the long shoot – produce crown of leaves and reproductive structures. Leaves - bilobed , fan – shaped – deciduous – golden yellow when they are shed – resemble Adiantum – so called “Maiden hair tree”. Root - tap root .

7. ANATOMY Root Anatomy – diarch . Endodermis with conspicuous thickening on radial walls ( casparian thickening). Pericycle broad. Sec. growth – as usual – but annual rings not so conspicuous. Xylem parenchyma – some cells with crystals. Phloem – with thick walled fibres. VAM found in the roots. Fontana 1985, reported Glomus epigaeum fungus from roots. Growth of seedlings increased when inoculated with G. e pigaeum .

8. Stem Anatomy – Epidermis highly cuticularised . Cortex & pith prominent and large. Tannin cells, Ca-oxalate crystal cells, etc. found in outer cortex. Large mucilage canals in inner cortex. Old stem – cortex with fibres & sclereids. Long shoots – cortex & pith small. . Pri . structure like other gymnosperms. Sec. thickening as usual. Wood is brittle & of no commercial value. Xylem & phloem as in others. Rays uniseriate. Trachieds narrow, X-parenchyma with Ca-oxalate crystals. So Ginkgo wood differs from other Coniferales. Dwarf shoot with manoxylic wood & phloem with crystals & so similar to Cycads. Cork cambium also formed.

9. Long Shoot – cortex & pith narrow, few mucilage ducts present, wood is hard & pycnoxylic & leaf traces few as leaves are scattered. Dwarf Shoot – cortex & pith more, more mucilage ducts present, wood is less, manoxylic & double leaf traces in dwarf shoot due to crown of leaves. Leaf Anatomy – wavy margins – Upper & lower epidermis – thick cuticle. Stomata sunken – present on lower side - haplochelic . Mesophyll with palisade & spongy in leaves of long shoots. No palisade in leaves of dwarf shoots. Mucilage canals seen in mesophyll between the veins. Vas.bundles many – each with sclerenchymatous & crystal celled bundle sheath.

10. REPRODUCTION Most primitive among living seed plants. Heterosporous – dioecious. Male & female trees indistinguishable till cones are produced. Male cone – axillary, not compact – a loose structure resembling a catkin inflorescence - central axis 2.3 to 3 cm with 2 vas. traces. Microsporophylls stalked & spirally arranged. Each sporophyll – has a slender stalk with knob-like hump or projection & 2 pendant sporangia – longitudinal dehiscence – lines face each other. Hump has a mucilage cavity – which on shrinkage pulls the sporangia apart – lines are exposed & pollen shed.

11. Female cone – greatly reduced – axillary in origin of a leaf or scale leaf – with a long peduncle – that bifurcates at apex & each branch bears a single ovule. Of the two ovules 1 aborts. Sometimes both develop into seeds. At the base of ovule – a rim of swelling present – the collar – it sometimes grows into a leafy structure – hence it represents a reduced megasporophyll. Collar originates after integument – devoid of vas. supply. Ovules of Ginkgo are considered as cauline & terminal on lateral axes. MICROSPOROGENESIS - Same as in other gymnosperms

12. POLLINATION – by wind – pollination drop. FERTILIZATION – Zygote formed. EMBRYOGENY Zygote nucleus 256 free nuclei Cells of micropylar region elongate rapidly to form massive suspensor Cells of chalazal region develop into proembryo / embryonal mass. Cotyledons 2 – rarely 3 A weak coleorrhiza present. SEED Bilaterally symmetrical. Of two ovules - one aborts – so each branch has one seed – germination is hypogeal. Fruit – orange red coloured – emits offensive smell.