Practical: Study of Nostoc

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 Practical: Study of Nostoc Nostoc is a filamentous, photosynthetic cyanobacterium. It commonly occurs in freshwater, moist soil, wet rocks and other damp habitats. Colonies are usually gelatinous because numerous filaments remain embedded in a mucilaginous matrix. Materials Required Fresh or preserved Nostoc material, clean glass slide, cover slip, dropper, dissecting needle, water, blotting paper and compound microscope. Procedure Take a small quantity of Nostoc colony with the help of a dissecting needle and place it on a clean glass slide. Add one or two drops of water and gently tease the material so that the filaments become separated. Place a cover slip carefully over the material without trapping air bubbles. Remove excess water with blotting paper. First observe the preparation under low power and then under high power of the compound microscope. Observations The plant body of Nostoc is thalloid and usually forms a soft, jelly-like colony. A colony contains numerous ...
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Affinity of Gymnosperms with Pteridophytes

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Affinity of Gymnosperms with Pteridophytes : 

The gymnosperms resemble the pteridophytes by the following features :


(1) Both possess independent sporophytes which are differentiated into root , stem and leaves . Both the groups exhibit heterosporous life cycle .

(2) The sporophytes possess a well developed vascular system such as xylem and phloem . The xylem in most of the members of groups lacks vessels and the phloem lacks companion cells .

(3) Many Cycads resemble the ferns in possesing large compound leaves and the in the circinate ptyxis of the leaves . Dichotomous venation in Ginkgo and ferns .

(4) The female sex organs are archegonia in both the groups .

(5) The male gametes of Cycads and Ginko are motile , like the pteridophytes . 

(6) Many pteridophytes like Marselia,Salvinia , Azolla, Isoetes and Selaginella are heterosporous like the gymnosperms .


( 7 ) Some of the heterosporous pteridophytes possess one megaspore in the megasporangium , like the gymnosperms .

( 8 ) The gametophytes of gymnosperms and heterosporous pteridophytes are endosporic .

(9) In both , the gametophytes are highly reduced and they are developed within the spore wall in some pteridophytes . The male gametophytes of heterosporous pteridophytes and majority of gymnosperms possess only two male prothallial cells .

(10) The female prothallus develops before fertilization and there is free nuclear division .

( 11 ) Development of a distinct embryo after fertilization . The embryogeny is endoscopic in many pteridophytes and all gymnosperms .

( 12 ) Germination of spores is precocious in gymnosperms and heterosporous pteridophytes . 

( 13 ) In the life-history, both sporophytic and gametophytic generations alternate regularly with each other .










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