Gymnosperm: General characteristics

   Gymnosperm 

 Characteristic feature
Distribution

• throughout the temperate and tropical regions and even in Arctic zone
• in India mostly found in hilly areas very few species grow in Plains like cycadales.
• Living gymnosperm are perineal xerophytic, Woody evergreen plant none of them are annual.

External features

• plant body is sporophytic and differentiated into root, leaf & stem
• the gymnosperm sequoia world tallest tree ( the giant Redwood) 125 M height and 30 M with 4000 year old in Redwood Park( California)
• smallest gymnosperm Zamia with underground tuberous stem .
• Tap root system,  sometimes symbiotic relationship with algae and fungi found
• in cycas root show symbiotic relationship with algae
• in pinus root show symbiotic relationship with fungi.
• stem usually erect profusely branched( unbranched in cycas) tuberous in zamia
• Leave scars on stem  are characteristic feature of  gymnosperms.
• the arrangement of leaves is spiral on stem or cyclic in some gymnosperm. The foliage of leaves of some coniferous are modified into long needles.
• Leaves maybe monomorphic( that is one kind leaves) and dimorphic (that is of two kind of leaves)
• in dimorphic, the foliage leaves are evergreen and protected by the cuticle whereas the scale leaves a minute and dioecious.

Internal feature 

• the vascular cylinder of roots maybe diarch or polyarch
• stem possess  Collateral endarch and open vascular bundle arranged in ring
• secondary growth occurs. secondary growth of occur by the activity of cambium
• xylem cosist of only tracheids and xylem parenchyma.vessels are absent (gnetals except).
• Phloem have sieve tube &phloem parenchyma but companion cells are absent.
• Stem show distinct secondary growth
• Woods are manoxylic type in cycas
• Pycnoxylic in pinus
• Leaves -Mesophyll of leaf is undifferentiated or differentiated into palisade and spongy parenchyma.
• Stomata are sunken.
• Most of the gymnospermic leaves do not  have ventral veins and translocation of nutirents take place by transfusion tissue.

 Reproduction

• Cones are usually monosporangiated but (ephedra species) are bisporangiated.
• Male microsporangia develop on abaxial side of micro sporophyll.
• Eusporangiate
• Megasporophyll may be similar to foliage leaves or cauline(pinus).
• Ovular integument have 3 parts-outer layer and inner layer is flashy but middle layer is stony.

• heterosporous plant usually produce two different type of spores  microspheres that is male megaspore that is female spores are found in sporangium.
• The microsporangium are born on lower surface of microsporophyll and megasporangium are born naked on megasporophyll
• microsporangium maybe arrange indefinite group called sori their number may be reduced to 2 in pinus
• microsporophyll are aggregated in a form of compact structure called male cone and megasporophyll usually aggregate in a form of female cone in some cases megasporophyll are falling in nature and not aggregated in a form of cones

• the male cone is short life and female cone are long life .female remain in plant until maturity and reaping of seeds.

• microsporophyll contain microsporangia. sporangium contain microspores  (distributed by wind always) microspores leavues microsporangia after 3 states normally but it diffeentr in different genes.

On germination

• micropile + Pollen form tube cells. microspores form male gametophyte that is haploid (one or two gametes)
• pollen grains get direct connected with a ovule  and deposit on Pollen chamber which after an unfavourable condition germinate here.
• Each Pollen Grain from Pollen tube have two functions
• 1-haustorial  that used to suck food and 2- sperm career
• That type of structure and functioning of pollen tube is termed as sphonogamic .
• female cone - megasporophyll which contain megasporangia  (ovule)
• ovules are orthotropous and   unintermic but bitegmic in gnetales
• haploid megaspores developed into female gametophyte which remain surrounded by integumin  that is endosperm.
• mature female gametophyte have( two or more or none) archegonia.this phenomena is called polyembryony .
• more then two mature female gametophyte in archigonia called polyembryony.
• each archegonia have single cell ,rentals Canal cell but neck Canal cells are absent .
• male sperm carry to archigonia through Pollen tube( in cycas Pollen tube only used to suck food from endosperm).
• female nuclei and male nuclei combine to form a zygote that is haploid zygote is first cell of sporophytic generation.

The young sporophyte

• zygote developed into embryo
• meroblastic development only Basil part develop to embryo middle and upper part developed into different things
• embryo develop at terminal part of the pressure which pushes the developing embryo into endosperm
• endosperm always haploid in nature because it develop before the fertilization MBA is
• endoscopic that means shoot Apex is directed opposite to micropile.
• the basic characteristic feature of gymnosperm is occurrence of polyembryony but only one embryo develops and mature
• mature embryo differentiated into leaf root stem number of cotyledons  in gymnosperms are one two or more 
• Cotlyodons are maybe in green in colour while still in close in seeds
• no true fruit are found in gymnosperm.