POLYTRICHUM (PIGEON WHEAT MOSS)​

CLASSIFICATION OF POLYTRICHUM (PIGEON WHEAT MOSS)​

Kingdom :-  Plantae

Division :- Bryophyta

Class :- Bryopsida

Sub Class :- Bryidae

Order :- Polytrichales

Family :- Polytrichaceae

Genus :- Polytrichum

Only three species of Polytrichum VlZ. P. densifolium, P. xanthopiium and P. juniperinum are found in India, mostly in hills. The species are found in a variety of habitats. Such as sandy ground, dry and stony places, peat, bog, marshy moores and damp soil, etc.

EXTERNAL FEATURES OF GAMETOPHYTE OF POLYTRICHUM (PIGEON WHEAT MOSS)​

• The gametophyte is differentiated into an underground rhizome and aerial, erect, leafy stems 20 cms or more tall. In P. commune, transitional zone between rhizome and upper leafy shoot is present.
• Rhizoids are produced by the rhizome. These are long and thick walled with oblique septa. The rhizoids coil round one another to form a rope like structure. These rhizoidal strands provide mechanical support also.
• The leaves on the rhizome and middle transitional region occur in 3 vertical rows. These are either brown in colour or colurless. The leaves on aerial leafy shoot are green, large and spirally arranged.
• Each leaf possesses a broad, colourless, membranous, one celled sheathing leaf base that narrows above into a lanceolate limb. The margins of the wings are coarsely toothed. The leaf has a dark green midrib.

ANATOMY OF RHIZOME OF POLYTRICHUM

• The transverse section shows an almost circular outline.
• It is differentiated into piliferous layer, cortex, endodermis and the central cylinder.
• A piliferous layer is the outermost. It bears rhizoids.
• This is followed by two or three layers of cortical parenchyma. It is interrupted by three hypodermal strands, the cells of which are distinctly prosenchymatous with pointed ends.
• Passing radially inwards from the hypodermal strands are cells of greater diameter, which do not show a clear demarcation with the cells of hypodermal strands. These are called the radial strands.
• The cortex is delimited from the conducting strand by large, radially elongated endodermal cells. The endodermis is discontinuous and consists of three arcs separated by radial strands.
• The central cylinder is trilobed. The central mass consists mainly of very thick-walled, elongated living cells (with oblique end walls), known as stereids. The stereids are collectively called as stereom.
• Scattered among the stereids are the hydroids which serve for the conduction. The hydroids are of about the same diameter as the stereids, or slightly bigger and as a whole being called as hydrome.
• Surrounding the trilobed central strand is an interrupted peri cycle composed of 2 or 3 layers.
• The furrows between the lobes are occupied by 6-8 polygonal cells known as leptoids, collectively called as leptom. These cells appear similar to sieve tubes.
• In between the leptom and hydrome is a layer of starchy parenchyma called as amylom.

ANATOMY OF AXIS OF POLYTRICHUM​

• The outline of the section is irregular due to attachment of leaves.
• The tissues show outermost superficial layer followed by cortex, peri cycle, leptom mantle, hydrom sheath, hydrom mantle and the hydrom cylinder.
• The superficial layer does not form clearly defined epidermis.
• The cortex is divisible into outer and inner cortex. The outer cortex is made of compact, elongated prosenchymatous cells gradually merging into the inner cortex made of parenchymatous cells. Leaf traces are quite common in cortex.
• Following the cortex is present the rudimentary pericycle which is not clearly differentiated.
• Inner to pericycle is the leptom mantle, the cells of which are typical sieve tube-like. The leptom mantle is regarded as equivalent to the phloem of vascular plants.
• Internal to the leptom mantle is the hydrom sheath (amylom layer) composed of one or two layers of cells with prominent starch.
• Immediately following the hydrom sheath is the hydrom mantle which is composed of thin walled cells without contents.
• The center of axis is occupied by the hydrom cylinder, made of thick walled cells.

ANATOMY OF LEAF OF POLYTRICHUM​

• The section shows several celled thick midrib that gradually merges into rudimentary wings which are made of hyaline cells.
• On the lower side is the cuticularized epidermis. Just inside the epidermis are one or two layers of small, sclerenchymatous elongated cells.
• The central tissue of the leaf is made up of large parenchymatous cells with some groups of sclerenchymatous cells scattered between them.
• On the upper surface there is a layer of large cells from which arise many parallel plates known as lamellae.
• Each lamella is uniseriate and is composed of 5-8 cells. Each cell contains chlorophyll. The terminal cell of each lamella is wider or papillose. Tenninal cells of the adjacent lamellae almost touch each other.
• These lamellae are the chief photosynthetic tissue of the leaf and compensate for the reduced wing.

ANTHERIDIAL BRANCH AND ANTHERIDIUM​

• Plants are usually dioecious and the antheridia and archegonia are present at the apices of the gametophores.
• The antheridia are surrounded by specialized leaves known as perichaetial leaves which are usually short and may be pale pink or rose. They form a cluster or rosette, superficially resembling a small flower.
• The antheridia are present in groups at the base of each perichaetial leaf in the position of lateral buds.
• Intermingled with the antheridia are the paraphyses. Some of the paraphyses are ftlamentous, whereas the others are broadened at their tips.
• A mature antheridium is usually stalked and somewhat club-shaped structure.
• It consists of a jacket of cells surrounding a mass of androgonial cells. (Since the apical cell is not consumed in the formation of the antheridia, the growth of the male shoot is not arrested by the development of antheridia. So after the antheridia have been matured, the vegetative axis may grow out in the following year through the antheridial cup and produce a new shoot. This new shoot may also behave likewise).

Archegonial branch and archegonium

• The archegonia are surrounded by coloured perichaetial leaves. This gives the appearance of a small flower.
• The archegonia are found in terminal groups at the apex of the gametophore, thus arresting the further growth of the axis.
• In each group there are usually three archegonia.
• Scattered among the archegonia are modified hair-like structures, the paraphyses.
• The archegonia are aIso stalked and greatly elongated and consist of venter and a neck.
• The venter is several cells thick and contains a venter canal cell and an egg.
• The neck consists of six vertical rows of cells and contains a large number of neck canal cells which disintegrate as the archegonium matures.

EXTERNAL FEATURES OF SPOROPHYTE​ OF POLYTRICHUM (PIGEON WHEAT MOSS)​

• The sporophyte is formed after fertilization and consists of foot, seta and capsule.
• The foot is buried in the tissues of the leafy gametophore.
• Just above and in continuation of the foot is the long and slender seta which support the capsule at its apex.
• With the growth of the sporophyte, the lower part of the archegonium enlarges following elongation, and is converted into a calyptra, covering the capsule.
• The wall of the capsule is several layered and the outermost layer is differentiated into an epidermis with thick outer walls. All the cells of the wall layers contain chloroplast.
• Inner to the wall there is an outer lacuna (air space), traversed radially by the chlorophyllous filaments. The filaments are connected internally with the outer wall of the spore sac.
• The spore sac is internally bound by an inner lacuna made of filaments that connect the spore sac with the central columella.
• The spore sac extends the entire length of the capsule. The archesporium (spore producing tissue) is 1 to 16 layered and all its cells develop into spore mother cells which after meiosis, give rise to spores.
• At the top of the capsule is present a lid, the operculum.
• Just below the operculum is present the epiphragm which stretches like a drum head over the opening of the capsule.
• Just within the mouth of the capsule and under the epiphragm is a ring of peristome teeth.
• At maturity peristomial ring is composed of 32 or 64 short pyramidal teeth. These teeth are not hygroscopic but control the dispersal of spores.

IDENTIFICATION OF POLYTRICHUM (PIGEON WHEAT MOSS)​

• DIVISION – Bryophyta
  1. True roots absent and instead are present the rhizoids.
  2. No true vascular strands.
• Class:- Bryopsida
  1. Gametophore erect and leafy,
  2. Rhizoids multicellular with oblique septa.
• Sub class :- Bryidae
  1. Leaves with distinct midrib.
  2. Seta long.
  3. Spore sac usually separated from the capsule wall by air space
• Order– Polytrichales
  1. Gametophores tall and perennial.
  2. Leaves narrow with lamellae on the upper surface of the midrib.
  3. Peristome teeth 32 or 64
  4. Calyptra, cucullate, either smooth spinulose or hairy.
• Family – Polytrichaceae
  1. Characters same as those of Polytrichales
• Genus – Polytrichum
  1. Rhizoids rope-like
  2. Capsule angular

REFERENCES

• https://en.wikipedia.org/wiki/Polytrichum
• https://depositphotos.com/stock-photos/polytrichum.html