Soral evolution in ferns

Soral evolution in ferns

1. SORAL EVOLUTION IN FERNS Presented by… Sumra Kazbanu A. M.sc sem – 1 botany CBO-402 Department of life science H.N.G.U. Patan

2. Contents: Introduction Types of sorus & it’s position in ferns Shap of indusium References

3. Introduction Defination of sorus: The group of sporangia is therefore,called a Sorus. OR the sporangia usually occur in clusters called sori or sorus,found on the underside fertile leaves. In ferns,these from a yellowish or brownish mass on the edge or underside of a fertile frond. In some species they are protected during development by a Scale or Film of tissue called the INDUMISUM .Which forms an umbrella like cover. It may be unprotected and nacked.

4. There are some ferns in which the sporangia are nacked and occur scattered along the veinlets .they do not form sori.e.g .Leptoteris humenophylloles. In Todea burbara the sporangia are densaly scatted and are not covered by an indusium.the sori in case are ill defined.

5. Types of sorus Depending upon the nature of the sorus and stage of sporangial development the ferns are divided as: Simplices, Gradatae and Mixtae. 1.The Simple Sorus: The sporangia in such a sorus development simultaneously and all of them mature together. All sporangia within a sorus may be at the same stage of development (Simplices) The Simplices are primitive and extend to the Paleozoic.

6. In Simplices the size and area of the receptacle is fixed and only a fixed number of sporangia can be borne on it with all of them being at the same stage of development. They mature at the same time. The number of sporangia per receptacle varies between 10-12. In some cases the sporangia are borne in two series. E.g. Ophioglossum and Osmunda.

7. 2. The Gradate or Basipetal Sorus : The Gradatae with an oblique annulus, occupy a middle position and have been discovered in the Mesozoic. In such cases the internal space within the radial sorus gets filled by overlapping sporangia. Overcrowding results and there is no space for the proper dehiscence of sporangia and consequently some of them do not dehisce. This mechanical inefficiency can be solved by the elongation of the receptacle on which the sporangia are borne at different times and are at different stages of development (Gradatae). Moreover there is no simultaneous drainage of food by the developing spores.

8. The placentae or the receptacles are long and almost cylindrical.They bear mature or older sporangia at their distal ends and younger sporangia near the proximal or basal part.such a sorus is found in Dicksonia,Loxosoma,Trichomanes,Cyathea,Alsophila, etc….

9. 3. The Mixed Sorus Mixtae annulus is present but in a vertical fashion. The spores are released in a staggered fashion and even if the environmental conditions are not favorable when the spores are initially released; this problem is solved by a constant crop of spores over a given length of time. This is an evolutionary advanced feature for survival. The next step in the evolution of the sorus is the mixed sorus (Mixtae).

10. Such a sorus is an aggregation of old and young sporangia that occur mixed and show no regular arrangement in a sorus.The young and old sporangia are indiscriminately mixed.such a sorus is found in majority of the living ferns.e.g.Polypodiaceae(Adiantum,Pteris,Pteridium,Davallia)

11. Position of sorus in ferns In christensia the sori are nacked,circular and are irregular arranged between the lateral veins. In Maeattia,Angiopteris,Danaea etc…the sori are elongagated and are situated below the lateral veins. The Ophioglossales are group of interesting ferns in which the sporangia are marginal in position.

12. The sporangia in Osmunda ,Davalia,Trivhomanes and many other ferns are also marginal in position In Glecheniaceae, the sporangia from distinct sori on the ventral surface of the leaves. The sori in Mattoniaceae are ventral in position and are usually arranged in two rows on either side of the midrib. In Adiantum the sporangia developon the underside of special marginal flaps of lamina that become reflexed and protect the sorus.

13. In Marsileales and the Salviniales the sporangia develop in sori that are borne within distinct structure called the Sporocarp. The sporocarp in Marsilea enclose sori that contain both micro and megasporongia. In Salviniales the smaller sporocarp contain many microsporangia each and the larger ones contain one or more megasporangia per sporocarp.

14. Indusial protection Some sori are naked others have an indusium for the protection of young developing sporangia. The shape and form of the indusium, method of attachment are variable. The indusium may be formed as an epidermal outgrowth covering receptacle and sporangia (true indusium) or it may merely be the in turning of the margin of the leaf to protect the sporangia (pseudo indusium or false indusium).

15. The indusium is reniform in Dryopteris ,circular in Polystichum lobatum ,funnel shaped in Davalia ,elongated and curved in Asplenium lanceolatum , Lamaria spicant and Blechnum occidentale ,In Matteuccia struthiopteris the indusium is cup shaped with denate margins.

16. References Botany for degree students; By: P.C.Vashishta A.K.Sinha Anil Kumar Diversity of Microbes and Cryptogams Pteridophyta By: prof.S.P.Khullar

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