Physcia

Physcia

Physcia

General structure

Physcia is foliose lichen. Physcia is divided into four regions internally. These regions are:

1. Upper cortex: It is present at the upper regions. It is composed of closely packed hyphae. Spaces are absent between them. if spaces are present, they are filled by gelatinous material. The upper surface may be smooth or it has hair like structures. These hairs are formed by scattered hyphae above the cortex.

  1. Algal layer or gonidal region: It is present below ti e upper cortex It contains algal components. Loose hyphae are present between the algal cells.
  2. Medulla: A wide region of loosely arranged hyphae is present below the algal region. It is called medulla. It forms the major part of the thallus.
  3. Lower cortex or hypothallus: It is present below the medulla. It is a narrow layer of compactly arranged hyphae.
    Physcia thallas

    Physcia thallas

    If the algal components are scattered irregularly among thz fungal hyphae. Then the thallus is called homoiomerous. If they are restricted to a single layer, then it is called heteromerous.

    Isidia: The surface of Manus is wavy. Small outgrowth isidia are formed on the surface of thallus. Each isidium consists of external cortical layers. It encloses the internal algal layer. Insdia increases the ;urface area for photosynthesis. It may detach from the thallus and give rise new plant.

    Breathing pores: Small cavities are present on the upper cortex. These cavities are called breathing pores. These cavities may be raised to form papillae or cone like structure.Cephalodia: Gall like outgrowth is formed on certain thalli. These galls are composed of both fungal and algal cells. These

    are called cephalodia. Reproduction Vegetative Reproduction Vegtative reproduction take; place by soredia formation. Soredia are Small  bud like outgrowths formed on the surface of thallus. Soredia are composed of rt.any algal cells with few fungal hyphae. The:’ may be present in patches called sorelia. Soredia are detached. They are dispersed by wind.

    Asexual reproduction

    Asexual reproduction in Physcia takes place by pycnospores formation. These spores are formed inside the flask shaped cavity called pycnidia.

    Sex Jai reproduction

    (a)   Ascogonium: The female reproductive. rgan is ascogonitim in “Physcia. Ascogonium is multicellular called structure. It has among multicellular trichogyne at its tip.

    (b)   Spermatangia: 1he male sex organs are spermatangia.

    Spermatangia are flask shaped. The) are embedded on fle upper surface of the Malik’s. Spermatangium opens out side by an astiole. Many spermatia are formed in the inner surface of spermenatangia.

    Fertilization: Spermatia are discharged form the spennatangia. They fall an trichogyne. Wall is dissolved bemeen two. The contents of sPermatium are transferred into trichogyne. Plastnogamy occurs. After that ascogonium produce ascogenous hyphae. The hyphae proauce characteristics fruiting bodies apothecia. Ascogenous hyphae produce asci inside the apothecia. Some sterile hyphae among the asci form paraphyses. Karyogamy occurs. It produces

    zygote nucleus. Zygote divides by meiosis. Then each cell divides by mitc sis. Thus each ascus contains eight ascospores. The peridium of apothecia also contain algal component. This condition is called lecanorine. Ascospores are dispersed by wind.

    Germination of ascospore: The ascospores germinate to produce hyphae in all directions. Some of its branches come in contact with the alga. They form many branches and surround the algal comoonent. More hyphae are formed. It produces characteristic thal Ms of Physcia.

    Section of apothecia of Physcia

    Section of apothecia of Physcia

     

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