psilotum:habit,distribution,reproduction,
synangia
psilotum:
Division:psilophyta
Class:psilophytinae
Order:psilotales
Family:psilotaceae
Genus:psilotum
Dusrtibution & habit:
- · Found in tropical and sub-tropical regions of the world.
- · In india,it is found in west Bengal,Madhya Pradesh,himachal Pradesh,assam,Andhra Pradesh,tamilnadu,kerala,karnatttaka,Maharashtra.
- · Grow in areas of high moisture.
- · Can grow on soil or more generally epiphytic or in rock crevices.
- · Plants growing erect are generally shorter
- · Epiphytic plants are pendulous.
Plant body:
- · Plant body distinguished into two parts
- · 1)basal rhizome:embedded in the soil,dichotomously branched,with scales and rhizoids which are generally 3 celled.
- · 2)aerial stem:green,erect and dichotomously branched.
- · The aerial branch does not have foliage leaves and hence the stem performs the function of photosynthesis.
- · Scaly leave are present.
Anatomy of
the stem
- · Broadly circular with wavy margins
- · Single layered epidermis with stomata
- · Outer cortex composed of few layers of chlorenchyma
- · Middle cortex is made up of 3-7 layers of sclernchyma.
- · Inner cortex is largely parenchyma
- · The stele is a prostele-actinostele.
- · Outer most endodermis.
- · Inner to it the pericycle.
- · The xylem is in the form of a star.
- · Xylem development is exarch.
- · Surrounded by phloem.
Reproduction
Vegetative reproduction by gemma.
Spore
production:
- · Produced in specialized bodies called synangia-3 sporangia
- · They are found in the axil of a distinct bilobed appendage.
- · The synangia appear yellow in colour when mature.
The synangia:
- · The sporangial wall is madeup of3-4 layers of cells.
- · At maturity the outer wall develops thickenings.
- · Three sporangial chamber are found
- · At the middle ther is a vassssscular strand.
- · Within each sporangial chamber are SMCs(sporangium middle chamber) which undergo meiosis to form haploid spores.
- · Psilotum is homosporous.
- · Spores are oval in shape with a long narrow ridge.
The
gametophyte:
- · The spore germinates slowly to give rise to the gametophyte
- .
- · It is associated with an endophytic fungus and is an irregular dichotomously branched structure.
- · Usually 1-15 mm in size in length and 0.5-1.8 mm in width.
- · They are colourless or yellow brown in colour.
- · They bear numerous rhizoids all over the surface.
- · The gametophyte is generally characterized by parenchymatous cells.
Reproduction
in the gametophyte
- · The gametophytes are monoecious and sex organs are scattered all over the surface of the thallus.
- · The antheridia and archegonia are intermingled with each other.
- · The mature antheridia are more or less globular structures without any stalk.it has a single layered wall which encloses several androcytes.
- · The mature archegonia consists of 4 rows of neck cells with 2 NCC(neck canal cell)it has a VCC(venter canal cell) and one egg.
- · There is no sterile structure surrounding the venter as it is embedded in the thallus.
- · Fertilization occurs in the presence of water.
- · The zygote gives rise to the sporophyte.
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