I B.Sc. THEORY NOTES

XYLARIA

The genus xylaria includes about 200 species. It is cosmopitan in distribution. Most of the species are saprophytic. They are found dead rotting stumps of trees, termitaria, derbis etc. It is commonly called ''Candle snuff'' or ''dead man's finger's" . A few species are parasitic. For example Xylaria mali  that attacks apple and causes "black root-rot" disease. Common indian species are Xylaria hypoxylon , Xylaria polymorpha , Xylaria mali  etc.

Vegetative structure :-

  The vegetative body of xylaria is a mycelium. It consists of profusely branched septate hyphae. Some of the hyphae coalesce to form an elongated strand. This strand is positively heliotropic  i.e., moving towards light. It becomes an elongated stroma.

  The mycelium growing in the decaying wood produces a cushion-shaped  structure called sclerotium. The sclerotium consists of compactly interwoven hyphae. From this sclerotium, club shaped structures arise and grow erect. They are called stromata.

Reproduction:-

Two types:- 1)Asexual reproduction

           2)Sexual reproduction

Asexual reproduction:-

  Takes place conidia. Conidia are borne or palisade like conidiophorus found on the surface of the young stromata. The stroma arises from a mycelium. It is made up of a compact mass of fungal hyphae.

  A palisade layer develops on the surface of the stromata. The terminal part of the fungal hyphae in the palisade layer cuts of conidia. They are not produced in chains. They are greyish white  in colour. They cover the surface of the stroma. The mature conidia detach from the stroma and disseminated by the wind.

  On reaching a suitable substratum, the conidia germinate and gives rise to new mycelia.

Sexual reproduction:-

  Sexual reproduction takes place in xylaria. But sex organs have not been recorded so far. The stroma bears many perithicia (fruit bodies). So it is believed that sexual fusion might have taken place within the stroma.

*Stromata (sing stroma) are black club-shaped , often branched structures formed from the sclerotia (sing sclerotium).

*Stromata of Xylaria polymorpha  are thick, black in colour and branched. They may attain a height of 8cm or more. They have a short stalk.

*Stromata of Xylaria hypoxylon  are stag horn  shaped and unbranched. They grow up to 3-4cm in height.

*Older sttomata develop perithecia.

*Antheridia are altogether absent. But there isa long coiled uninucleate ascogonium  in the stromata.

*The haploid nucleus in the ascogonium divides repratedly so as to form 20 or more nuclei. The ascus gets segmented in such a way so as to form a chain of binucleate cells.

*An ascogenous hypha is branched and septate. It produces a hook(crozin) just behind the terminal cell. The terminal cell of the ascogenous hypha acts as ascus mother cell.

*The two haploid nuclei in the ascus mother cell fence together ro form a diploid nucleus. It is called synkaryon. The stage represents the diploid phase in the life cycle.

*The diploid ascus nucleus in the ascus mother cell divides meiotically and then mitotically to form 8 haploid nuclei.

*Each nucleus gather a piece of cytoplasm to giverise to an ascospore.

*The ascus mother cell becomes an ascus. The mature ascus contains 8 ascospores.

Structure of perithecia (sing Perithicium):-

*A cluster of asci together with sterile hyphae forms a fruiting body called perithecium.

*Perithecia develop from older stroma.

*The young perithecia are globose but they become flask-shaped when matures.

*The neck of each perithecium slightly protrudes out of stroma, and has an openimg called ostiole. Which is lined by sterile hyphae called periphyses (sing periphyses)

*The inner cavity of the perithecium is lined with a fertile zone called hymenium.

*The hymenium is made up of compactly arranged asci and some sterile hyphae called paraphyses.

*The rim of the peritheciumbis made up of pseudoparenchymatous tissue of the stroma.

*Each ascus is an elongated cell containing 8 ascospores, which are asymmetrical.

*At maturity, the asci elongate, and swell up by absorbing some amount of water. It generates some force ro rupture the ostiole, ro release ascospores.

*They dry up on the surface of stroma. The ascospores are disseminated by wind.

*After reaching a suitable substratum, each ascospores germinate and give rise to a new mycellium, which is haploid.

Systematic position:-

Kingdom: Mycota

Diviaion: Eumycota

Class: Ascomycetes

Series: Plectomycetes

Order: Sphariales

Family: Xylariaceae

Genus: xylaria

Digitised by

Sumanth Devadiga

1^st B.Sc (BZC)

PEZIZA (Cup Fungi)

It is a saprophytic , very often coprophilous in habit. It frequently grows on dung,rotting wood,...etc some species of this genus grow on burnt or charned wood .

The species commonly found is Peziza vesiculosa ... It is one of the larger cup fungi and is cosmopolitan in distribution.Peziza genus includes about 160 species, of these 13 species have been recorded from India. Some common Indian species are Peziza vesiculosa Peziza bodia,  Peziza repanda,Peziza pustulata, Peziza catinus, Peziza aurantia ...etc..

Vegetative Mycelium :-it is well developed, frequently perennial and consists of a dense network of hyphae. The hyphae are branched and septate  the cells are uninucleate . The hyphae are hidden within the substratum. They form a complex system which extracts nourishment from the substratum. The fruiting bodies are above the ground. The protoplasm is granular and the nuclei are typically eukaryotic.

Reproduction :- Peziza reproduce by two methods.They are  
 1. Asexual method 2. Sexual method 

Asexual reproduction :- Takes place by the formation of conidia and chlamydospores. The conidia are exogenously formed spores. They are produced at the tips of conidiophores. Each conidium is a small, globular, uninucleate cell, on germination gives rise to a new mycelium.

Chlamydospores are thick walled spores, which are produced singly on in groups within the cells of the mycelium, during unfavourable environmental conditions. Under suitable conditions, the wall of the vegetative cell ruptures, chlamydospores come out and get disseminated by wind. On reaching a suitable substratum, they germinate and form new mycelia.

Sexual reproduction :-Sexual reproduction has been reported in Peziza,but sex organs are no longer noticed . Here the vegetative cells behave as gametangia to produce sexual union. So sexual reproduction is Known as somatogamy.

The sexual process is extremely simplified. The mycelium of peziza looks like a tangled mass of hyphae. Some vegetative cells in the centre of the tangled mass start to function as gametangia. When these cells approach each other, the cell wall dissolves at the point of contact, leaving a pore. The nucleus of the vegetative cell goes to the other cell through the pore. As a result dikaryotic condition is attained. These pairs of nuclei are called the dikaryons. The dikaryotic condition is brought about either by autogamous pairing or by somatogamous copulation between the vegetative cells of the adjacent hyphae of the tangled hyphal mass. The cells with the dikaryons give rise to the ascogenous hyphae. Which becomes multicellular by cross walls. Their cells are binucleate .

* The terminal binucleate cell of each ascogenous hypha functions as an ascus mother cell

* The ascogenous hyphae and dikaryotic cells from which they are developed together with the ascus mother cells represent the dikaryoticphase in the life cycle of Peziza

* The two nuclei of the ascus mother cell fuse to form the synkaryon.

* The young ascus with the synkaryon represents the transitory diplophase.

* The synkaryon undergoes successive three divisions.

* Of these the first and the second constitute meiosis the third one is mitotic division.

* This results in the formation of 8 nuclei which are haploid, later each develops into an ascospore.

* The mature ascus is an elongated, cylindrical cell, enclosing 8 ascospore.

As there is development of aeciospores the mature mycelium produces one or few fruiting bodies called apothecia.

Structure of apothecia:-

* The apothecia are large, fleshy, about 5 cm in diameter,sessile or subsessile cup shaped bodies .

* The cup is white or buff -coloured from outside but end interior of the cup is brown or bright scarlet in colour.

* The inner ling of the apothecium is called hymenium which consists of a large number of asci interspread with sterile hyphae..

V.S of apothecium 

* V.S of apothecium shows cup shaped structure consisting  of mycelium.

* The basal portion of the apothecium is called hypothecium which is made up loosely packed fungal mycelium forming a pseudoparenchyma.

* The hypothecium remains attached to the underlying mycelium present in the substratum.

* The outer layer of hypothecium called peridium.

* The inner lining of apothecium is called hymenium layer consists of a large number of asci arranged in a layer in pelisade manner.

* The asci are intermixed with sterile hyphae called paraphyses.

* The asci and paraphyses are parallel to each other and perpendicular to the surface of the hymenium due to the fact that they are positively photosynthetic  and grow towards the light.

* Each ascus is long, cylindrical, club shaped structure, and possess eight ascospores

* The ascospores are unicellular , uninucleate, thin walled spores produced as a result of sexual reproduction.

* They are arranged linearly and placed obliquely inside the ascus. The mature ascus absorbs moisture and swells up to a considerable extent. Because of this reason, the ascus wall ruptures and ascospores are released out. These spores dry up by the sunlight and dissiminated by wind. On reaching suitable substratum, the ascospores germinate and give rise to mycelium which is haploid .

Systematic position:

Kingdom : Mycota

Division : Ascomycotina

Class : Ascomycetes

Sub class: Euascomycetidae
Series:Hymenoascomycetes
Sub-series:Discomycetes
Order : Pizizales

Family : Pezizaceae

Genus : Peziza

Species :vesiculosa 

Digitised by

Shravana.K

1^st B.Sc (BZC)