CLASSIFICATION OF POGONATUM
Kingdom :- Plantae
Division :- Bryophyta
Class :- Bryopsida
Sub Class :- Bryidae
Order :- Polytrichales
Family :- Polytrichaceae
Genus :- Pogonatum
Pogonatum is the largest genus with about 199 species distributed allover the world. Of these, 34 are found in the temperate hills of India and Sri Lanka. It is commonly found in the hills of India, growing on the rock soil. The most common Indian species are P. aloides, P. microstomum, P. junghunianum, etc.
EXTERNAL FEATURES OF GAMETOPHYTE OF POGONATUM
- The gametophyte is differentiated into rhizoids, stem or axis and leaves.
- The basal rhizomatous part of the erect stem is slightly stouter and stiffer. It bears rhizoids.
- The rhizoids are thick walled and multicellular. The septa are oblique. Many rhizoids twist together in a rope-like manner forming strong cable-like strings.
- The aerial part of the stem bears leaves. The leaves on the lower part are very small, scalelike and much paler in colour.
- The upper leaves are crowded together spirally, spreading out from the stem and are rather stiff.
- The leaves are sessile, pale in colour with sheathing broad base. The upper part of the leaf is deep green to brown or reddish brown in colour. The leaves gradually taper towards the apex and the margins are serrated.
- A leaf has a distinct thick midrib in the center with narrow wing-like lamina on either sides.
- The upper surface of the midrib is completely covered by parallel longitudinal vertical platelike structures called lamellae.
ANATOMY OF AXIS OF POGONATUM
- The transverse section shows epidermis, cortex, leaves leptoid mantle, stereids and hydroids.
- The outermost single layer of slightly thick walled cells is the epidermis. It is broken in the upper part of the stem due to presence of leaves.
- A wide zone of cortex follows.
- It shows outer and inner regions. The cells of the outer cortex are thick walled, elongated and deeply coloured.
- The inner cortex is wider than the outer. The cells are thin walled, parenchymatous, lighter and compact.
- A few thick walled leaf traces are also found in the cortex.
- Inside the cortex is a zone of elongated cells with protoplasm but no starch. The cells are considered to be similar to sieve tubes and show oblique intervening cells like sieve plates. The cells are leptoids. This zone is called as leptoid mantle.
- The center of the stem shows hydrom cylinder which is made of two types of cells-the elongated, thick walled cells with living contents called stereids and similar cells devoid of contents called hydroids.
- Hydroids are dispersed amongst stereids. They are considered to be helpful in water conduction.
MALE PLANT AND THE ANTHERIDIUM OF POGONATUM
- Antheridia are borne at the apex of the branches of male plants.
- Antheridia are surrounded by specialized leaves, the perichaetial leaves, at the apex. These are coloured red or orange and form a flower-like head.
- The group of these leaves enclose a cluster of antheridia and paraphyses.
- The antheridia are borne in such a way that the center of the axis remains free for further growth.
- Each antheridium is a club-shaped structure with a short stalk.
- The stalk is multicellular and holds the body of the antheridium.
- The body of antheridium is made of a single layered jacket that surrounds many androcytes.
- Many paraphyses occur scattered amongst the anteridia. Paraphyses are long, multicellular, hairlike structures with rounded apical cell. Each cell has many chloroplasts.
FEMALE PLANT AND THE ARCHEGONIA OF POGONATUM
- An archegonial cluster develops at the tip of the plant.
- Each cluster consists of archegonia and paraphyses, surrounded by perichaetial leaves.
- Perichaetial leaves are specially modified leaves located at the apex.
- During the formation of archegonia, apical cell is used up and hence the axis stops any further growth.
- The archegonium is attached to the stem apex by a short multicellular stalk.
- The archegonium consists of a neck and a ventre. The neck consists of six vertical rows of cells, two cover cells and 8-12 (or more) neck canal cells. The ventre is made of venter canal cell and an egg cell. The wall of the ventre is made of 2 layers of cells.
- The paraphyses occurring among the archegonia are multicellular, long, hair-like structures made of single row of cells. The cells are rich in chloroplasts.
SPOROPHYTE OF POGONATUM
- The mature sporophyte consists of a foot, seta and a capsule covered by a calyptra.
- L.s. of the capsule shows a lower stalk, middle fertile region and the upper operculum.
- The stalk consists of a parenchymatous tissue that merges with columella. It is surrounded by chlorophyllous cells.
- The capsule lacks a basal apophysis with stomata.
- The fertile region of the capsule shows the following structure.
- One layered epidermis with thick outer walls.
- Several layered wall of chlorophyllous cells.
- Large cylindrical air space or outer lacuna connected by string-like fllaments of green cells with outer wall of the inner spore sac cylinder.
- The spore sac has an outer one layered wall and inner two layered wall consisting of thin walled cells.
- The spore sac is usually two layered thick. It shows archesporial tissue when young and spores when mature.
- Inner spore wall is followed by another air space (inner lacuna).
- The green fllaments of inner air space are connected with centrally located parenchymatous columella. It is not cylindrical but produces four wing-like extensions.
- Columella passes into opercular region and swells up to form drum-like roof of the capsule called epiphragm (tympanum).
- Above the epiphragm is a conical and beaked operculum which is connected to the capsule by a ring-like diaphragm. Organised annulus is absent.
- Above the diaphragm is a ring of 32 short peristomial teeth. These are formed of the bundles of fibrous cells. The teeth are hygroscopic and control the dispersal of spores.
IDENTIFICATION OF POGONATUM
- DIVISION – Bryophyta
- True roots absent and instead are present the rhizoids.
- No true vascular strands.
- Class :- Bryopsida
- Gametophore erect and leafy,
- Rhizoids multicellular with oblique septa.
- Sub class :- Bryidae
- Leaves with distinct midrib.
- Seta long.
- Spore sac usually separated from the capsule wall by air space
- Order – Polytrichales
- Gametophores tall and perennial.
- Leaves narrow with lamellae on the upper surface of the midrib.
- Peristome teeth 32 or 64
- Calyptra, cucullate, either smooth spinulose or hairy.
- Family – Polytrichaceae
- Characters same as those of Polytrichales
- Genus – Pogonatum
- The leptoid and hydroid cells poorly demarcated
- Neck or apophysis absent from the capsule
- Peristomial teeth solid, 32 in number.