GYMNOSPERM

GYMNOSPERM

• The term of gymnosperm was proposed by Theopharatus
• Gymnosperm and angiosperms was collectively called spermatophyte (I.e seed bearing plant)
• It is marked seed plant that means fruits and flower do not formed in them 
• In Angiosperm embryo, seeds and fruits are formed.
• In Angiosperm seeds are enclosed in fruit.
• The distribution of Gymnosperm is very limited. Mainly found is cold regin.

I.e slopes of Himalayas.

• Almost all Gymnosperm are sprophyte (desert plant)
• Leafs of Gymnosperm are well adapted to tolerate extreme of temperature, humidity, and wind and may be niddle like to refuse the surface area and they have thick nautical and sunken stomata to reduce water loss.

Why  thick nautical leaf?

• As nautical layer present in all type of leaf but in deserted or cold area it is thick as to reduce transpiration and also its leaves can't photosynthesized due to thick layer at the surface.
• All Gymnosperm are vascular plant. The xylem do not contain vesicles and phloem do not contain companion cell is Gymnosperm 

Note:-

But , exception in some Gymnosperm that have vesicles.

E.X:- Gmetum, Ephedra, Welwitschia.

• Maximum Gymnosperm are small or tall trees. But Emhedrs is a shrine and only one member Gnetum is a woody climber.

Life cycle

• The main plant body is saprophytic (2n).
• Most of Gymnosperm are diosious (I.e:- Male and female plants are separate)
• All the member of Gymnosperm are heterosporous. (I.e. two types of spores are formed during reproduction.)
• Microspore (Male), and Megaspore (Female)
• These two types of spore are formed in two different sporangia.
• Microspore are formed in microsparangia.
• Megaspore are intugmented so called ovule.
• There are different types of sporangia that are formed on different sporophyll.
• Microsporangia are formed on microsporophyll and Megasporogia.
• These two types of sporophyll formed male and female cone respectively.
• Microspore are formed by meiosis in the cell of microsporangium. 
• Megaspores are formed by meiosis in the cell of megasporangium (ovule)
• Microspores germinate and formed malegametophyte (pollen grain)
• Malegametophyte forms male gametes.

Note:- Antheridia are absent in Gymnosperms.

Pteridophyte is the last group with antheridia.

• Male gamete are matile and multicellular in very few Gymnosperm while male gametes are non-native in maximum Gymnosperm (I.e. cillian and flafella are absent)
• Main body of ovule is made up of diploid tissue known as megasporangium.
• A cell of novellus acts as megaspore mother cell which undergoes meiosis and formed 4 hiploid megaspores
• Out of which 3 are degenerate and 1 remain functional.
• This megasporous further develops into female gametophyte or endosperm.
• The cell of endosperm behave like archigonial initials and formed two or more arachidonic.
• Achegonia:- It forms eggs (female gamete)
• Now pollen grain reaches the ovule by pollination 
• Pollination in gtmnosperm performed by wind.