Pteridophytes

 

Marsilea

 

Habit of Marsilea:

The plants are herbaceous with rhizomatous stem, creeping on or just below the soil surface.

The species of Marsilea are generally aqua­tic or amphibious in nature with their roots embedded in mud or damp soil. The aquatic species — M. minuta and M. quadrifolia — occur in fresh water ponds, shallow water, or in mud or damp soil.

 

Structure of Marsilea:

Sporophyte:

The sporophytic plant body of Marsilea shows differentiation of stem, leaves and roots (Fig. 7.116).

1. Stem:

The stem is long, slender and freely-branched rhizome of indefinite growth that grows on or just below the soil surface. It is differentiated into nodes and internodes. The internodes are gene­rally long in aquatic species but are short in sub- terrestrial or terrestrial species. The production of underground tubers on rhizome has been repor­ted only in M. hirsuta.

The outermost layer is epidermis, composed of compactly arranged thick-walled cells and are devoid of stomata. The cortex is extensive and differentiated into three layers viz., outer cortex, middle cortex, and inner cortex. The outer cor­tex is parenchymatous with large air spaces.

The air chambers are separated from each other by a single-layered septum. The middle cortex is scle­renchymatous, while the inner cortex is made up of compactly arranged parenchymatous cells. The air spaces are absent in xerophytic species (e.g., M. aegyptiaca).

The stele is amphiphloic solenostelic which occupies the centre of the rhizome. Xylem occurs in the form of a ring and is surrounded on either side by phloem.

The central part of the stele is occupied by pith which is parenchymatous in aquatic species and sclerenchymatous in xerophytic species (e.g., M. aegyptiaca). The stele is bounded externally by outer pericycle and outer endodermis, while it is bounded inter­nally by inner pericycle and inner endodermis.

Reproduction in Marsilea:

Marsilea reproduces vegetatively as well as by means of the spores.

 

i. Vegetative Reproduction:

 

Under some unfavourable circumstances the subterranean branches of the rhizome form tubers. These structures have reserve food in the form of oil globules which help them to over­come the unfavourable conditions. On return of the favourable conditions, these tubers germi­nate and form new plant body (e.g., M. hirsuta, M. minuta, M. erosa).

Bryophytes

 

Funaria

 

Distribution of Funaria

Funaria is the most prominent genus in the family Funariaceae. It is represented by about 117 species and is found in all parts of the world.

The species of Funaria are terrestrial mosses and grow as green velvety patches in shady and damp places such as moist walls, burnt soil, and the trunks of trees, during the rainy season.

Funaria hygrometrica is the most common species and is called cord  moss due to its twisted seta.

·         Some of the common Funaria species are F. hygrometrica, F. flavicans, F. apophysata, F. arctica, etc.

 

External Morphology

Funaria is divided into two stages: leafy gametophyte and sporophyte.

The gametophyte is the main plant body that is represented by a juvenile and an adult stage.

The haploid plant body is divided into stem, leaves and rhizoids.

The stem is erect, branched, green and photosynthetic. The branches arise from the lower portion of the stem.

The leaves are arranged spirally on the stem. They are scattered towards the base and crowded at the apex. They are sessile and almost ovate in shape and have a distinct midrib.

The stem is fixated on the substratum by rhizoids. They are branched, multicellular and appear like root hairs.

The gametophytic plants are monoecious and homothallic. The male reproductive organ or antheridium and the female reproductive organs or the archegonium are borne on different branches of the same plant.

Both the antheridium and archegonium are produced in clusters at the end of antheridial and archegonial branches, respectively.

The sporophyte is attached to the archegonium in parasitic nature and is divided into a foot, seta and capsule.

 

Internal Morphology of Funaria

Internal morphology, or the internal structure of the  plant body, is the anatomy of Funaria.

Axis or Stem Anatomy

In a transverse section, the mature stem of Funaria shows three distinct regions: the epidermis, the cortex, and the central conducting strand or central cylinder.

Figure: T.S. of stem showing different parts

Epidermis

The epidermis is the outermost layer of the stem. It is generally one cell thick and consists of small thick-walled tangentially elongated chlorophyll-bearing cells.

Cuticles and stomata or pores are absent in the epidermis.

Cortex

The cortex lies in between the epidermis and the central cylinder. It is many-layer in thickness and composed of large parenchymatous cells.

In the younger part of the stem, the cells of the cortex contain chloroplasts. However, they are lacking in the older section.

As the stem matures, the outer cells of the cortex become thick-walled and are reddish-brown in colour. While the inner cells of the cortex are thin-walled.

The cortex also contains isolated leaf traces (patches of small cells) in the peripheral region.

Central Conducting Strand or Central Cylinder

The central conducting strand or central cylinder is made up of long, narrow, thin-walled colourless cells. These cells lack protoplasm and are called hydroids (dead cells).

The hydroids possibly help in the upward conduction of water and mineral nutrients.

Leaf Anatomy

In a transverse section, the leaf of Funaria shows a well-developed midrib with two lateral lamina, or wings.

Figure: T.S. of leaf

The midrib is several cells thick. It has a small central strand of slightly narrow, thick-walled cells called stereids. They help in conduction.

The leaf lamina is made up of a single layer of parenchymatous polygonal cells. These cells are elongated, thin-walled, and contain large and prominent chloroplasts.

Reproduction in Funaria

Funaria reproduces by vegetative and sexual methods.

Vegetative Reproduction

Vegetative reproduction in Funaria occurs by the following methods:

Fragmentation of Primary Protonema

In Funaria, the spore on germination develops a branched, filamentous structure called the primary protonema.

Under certain circumstances, the primary protonema forms specific colourless separation cells by intercalary divisions. As these cells die, they break up the protonema into several fragments.

The fragments develop into new protonema. Each new protonema bears buds that grow into leafy gametophores.

Secondary Protonema

The protonema that develops from any part of the  plant other than the germination of the spore is known as secondary protonema. It may develop from any injured part of the gametophyte, such as rhizoids, stems, leaves, or reproductive structures.

Each secondary protonema forms buds and grows into gametophores

Fungi

 ALBUGO (CYSTOPUS)

                                                              

Occurrence: 

·         Most of the species of Albugo are obligate parasites occurring as endoparasite in higher plants.

·         They usually infect the member of the families’ cruciferae, convolvulaceae, compositae, amaranthaceae.

·         There are 30 species is found all over the world also species are present in India.

 

Symptoms:  

·         The fungus insects mainly the aerial parts of the plant such as petioles, leaves, stem, flowers and fruits.

·         The early symptoms of the disease are the formation of whit shiny irregular, pustules (spot) on the lower surface of the leaves.

·         Later on the pustules enlarge in size and fuses with each other to form large pustules. The host epidermis is ruptured and white powdery mass comes out at maturity.

·         The infected part of the form hypertrophied or distortion (eg- in leaf, stem). Infected flower become sterile.

Vegetative structure:

·         The mycelium of Albugo is well branched, aseptate and caerocytic.

·         The hyphal wall is composed of chitin and the cytoplasm is granular and contains many nuclei, vacuoles, oil globules and glycogen.

·         The fungus grows in intracellular space of the host.

·         Tissue and absorbs food material with the help of knob like haustoria.

·         The haustorium is differentiated into haustoria head and a slender neck like stalk.

·         Head of haustorium filled with dense cytoplasm and having all cell organells except nuclei.

·         The base of haustorium surrounded by cellular like sheath form by extension of host cell wall.

Reproduction:

 Albugo reproduces by asexual and sexual means.

1.      Asexual reproduction-

·         Asexually it is reproduced by multinucleate structure known as conidia sporangia or zoosporangia. It development are as follows.

a)      Formation of conidiophores or sporangiophore-

·         After infecting host tissue intercellular mycelium collects beneath the host epidermis.

·         The tips of these hyphae develop into short erect, thick walled and club-shaped structure called conidiophores or sporangiophore.

·         The aerial end of the conidiophores is multinucleate thin walled and densely cytoplasmic present just beneath of epidermis.

b)     Formation of conidia or sporangia or zoosporangia-

·         Conidia or sporangia develop in long basipetal chain at the tip of sporangiophore or conidiophores.

·         During the formation of the mycelium a deep constriction appears below the swollen end of the conidiophores which come out from the periphery and move toward the centre of the tip of sporangiophore.

·         At the last constriction develop into transverse wall and small bud like structure develops into a spherical multinucleate conidium or sporangium.

·         This process repeated for several time and each other with the help of disjunctor.

·         This newly formed conidia excreted the pressure on the wall of epidermis and ruptured the pressure on the wall and they come out from host surface as white powdery mass. Hence the disease caused by this fungus is known as white rust.

c)      Germination of conidia-

·         Conidia are smooth multinucleate and spore structure measuring 13-18µm in diameter.

·          Conidia are dispersed form the pustules by shrub and drying of the disjunctor.

·         They get below by wind or washed away by rain. They get germinate after 2-3 hours on suitable substratum under moist condition.

·         Multinucleate conidia divide into number of segment.

·         Each segment metamorphosed into reniform biflagellate zoospore.

·         These newly formed zoospores germinate and form a germ tube which penetrate through epidermis and develops into a fresh mycelium.

Sexual reproduction:  

In Albugo sexual reproduction is oogamous and male and female sex organs are known as antheridium and oogonium respectively. They develop in intracellular space quite deep into host tissue develop from male branch and female branch respectively.

Oogonium:

·         During oogonial development the apex of the hyphal branch swell considerably and becomes globular by accumulating cytoplasm and nuclei.

·         The swollen apex with 6-12 nuclei is separated from main hypha by the formation of a transverse septum.

·         The cytoplasm of the young oogonium is uniformly vacuolated and nuclei are evenly distributed throughout.

·         But protoplasm of oogonium differentiated into outer more vacuolated and nuclei present periplasm and central densely cytoplasmic ooplasm.

·         In between ooplasm and periplasm a membrane is form.

·         The ooplasm represent the egg. There are only one nucleus is present at the maturity of egg.

Antheridium:

·         Antheridia are elongated, club shape and multinucleate structure.

·         They develop on male hyphae which are placed very close to the oogonium.

·         The tips of the male hyphae accumulate cytoplasm and nuclei and swollen antheridial tip is soon cut off by transverse septum.

·         There are many nuclei in antheridia but only a single remain function and remaining get degenerate.

Fertilization:

·         Fertilization takes place by gametangial contact.

·         The wall of antheridium and oogonium become thin at the region of their contact.

·         The antheridium form a slender fertilization tube that penetrates the oogonial wall and through this tube plasmogamy take place also male nuclei fuses with that of female nuclei in it.

·         Fertilized egg secretes a thick wall around and knows it known as oospore. The wall of oospore differentiated into two layer outer layer known as exine while inner wall known as intine.

 

 

 

Germination of oospore-

·         The nuclei in the oospore divide meiotically after that mitotically and formed many haploid nuclei.

·         The protoplasm is also divide in number of segments in each segment one nuclei is present.

·         Each segment get metamorphosed into uninucleate reniform and biflagellate zoospore.

·          The zoospore germinate by absorbing water and form germ tube and this germ tube later on form mycelium of thallus.

    

 

Nostoc

 Classification

                                                   Division- Algae

                                                      Class -    Chlorophyceae

                                                      Order -      Nostocales

                                                    Family -          Nostocaceae

                                                     Genus -             Nostoc

 

Occurrence

·         It is filamentous form of both terrestrial and aquatic habitats.

·         It does not occur in single filaments but grows in large colonies of closely packed trichomes embedded in firm matrix of gelatinous materials

·         Nostoc colony occurs floating or attach to substratum.

·         The thalli are various size and shape and may be solid or hallow. They may be ball of jelly like substance or may be irregular shaped.

·         The colony may be olive green or blue green and the surface of the colony warty and smooth.

·         Terrestrial species of Nostoc grows on damp soil and forms leathery or rubbery sheath and common in artic and alpine meadows.

·         Aquatic species occur either a free floating thalli in the sunny pool, ponds and lakes at the bottom attached to the substratum.

·         Nostoc also occurs in symbiotic association with fungi to form lichens.

Structure of the colony           

            Innumerable chain of bead like cell (trichome) of varying length is intricately tangled in a copies gelatinous matrix to form a colony. Each trichome is usually enclosed by its own mucilaginous sheath and called as filament. The numerous filaments in the colony are held together by a soft mucilaginous envelope formed by a fusion of the individual trichome sheath. The mature one is large. When number of colony growing in neighborhood within a common gelatinous mass called as compound colony

Structure of trichome

           Each trichome is composed of numerous rounded or oval cells. The cells are joined loosely form end to end due to which resembling a string of beads. At frequent intervals along with trichome are found colourless, empty looking, spherical or barrel shaped cells called the heterocysts. They are slightly large and have thicker wall than the vegetative cells and are intercalary sometime terminal. Under certain condition vegetative cells become greatly enlarge with stored food and greatly thickened to become resting bodies called as akinetes. Each trichome with its individual sheath is called as filament.

Cell structure

            The cell consist of the cell wall surrounding the protoplast. The protoplasm here differentiated into two regions. Outer pigmented region called as chromoplasm and inner colour less region is called as centroplasm. The chromoplasm has usual pigments located in the lamellae which form a system of peripheral area of parallel paired membranous embedded in the granular matrix. The centroplasm is not separated from the chromoplasm by any kind of membrane.  

Reproduction

Noctoc reproduces entirely vegetatively by the following methods

·         Colony fragmentation

The Nostoc as filaments gets breaks up into the smaller filament due to storm and other disturbance. Each of these grows up into the size of the parent filament.

·         Harmogonia

Hatmogonia formation is very common in Nostoc.  The trichome rapture at some places where a heterocyst and vegetative cell join with each other.  This junction is weakest link in the chain. In this way shor t segments of living cells called as the harmogonia become isolated. The harmogonia slip out of enclosing gelatinous matrix and established new colonies by division. Sometime the harmogonia develop into fresh trichome without being liberated from the colonial sheath and form adult colony.

·         Resting spore or akinetes

Under certain condition any cell or some of the vegetative cells of the trichome  become enlarged and each secrets a thick, highly resistant wall around it. They have reserve food materials are called as akinetes or resting spore. These are well adopted to survive in unfavorable condition. With the return of favorable season each akinetes germinates to form new filament of Noctoc.

·         Endospore formation

The content of the heterocyst of Nostoc divide to produce endospores. The endospore on liberation gives rise to new filaments.  

References

1.  Vashishta, B. R., Singh, V. P. & Sinha, A. K. (2012). Botany for Degree Students - ALGAE. S. Chand, 1-624.

2.9eed7ce0820d5fb37542bcdbea84fb56.jpg (1560×1259) (z-dn.net)

3. Nostoc: Features, Occurrence, Structure, Reproduction (biologylearner.com)