Ferns come into a group of highly developed cryptogams and are broadly distributed all over the world. They are shadow and moisture-loving plants and thus, grow lavishly in cool shaded, moist locations both in the hills and in the plains. They fit in to the division termed Pteridophyta. A few live as epiphytes, growing on other trees, for illustration: Platycerium on the palm trees. A general and broadly distributed fern is Dryopteris.
Dryopteris is a land plant which grows in wet soil and beneath the shade of trees. It comprises of roots, leaves and stems. Ferns are generally perennial herbs having stems frequently in the form of a rhizome, through which they generally reproduce vegetatively.
The Ferns are amongst the aged land plants, dating back to the Carboniferous era (359 to 299 million years ago), when they considered to have been the dominant kind of vegetation. The fronds of several Carboniferous ferns are about similar with such of living species. Reproduction through spores preceded the growth of angiosperm reproduction.
Ferns range in size from several aquatic species a few centimeters high to a few tree ferns which can grow up more than 20 meters high with fronds above three meters.
Ferns encompass three main parts: The rhizome, the fronds and the reproductive structures termed as sporangia. The features of each of such three parts of the fern plant are employed for categorization and recognition.
The rhizome is basically the stem of the fern plant. It appears in three fundamental forms:
The fronds are the leaves of the fern. There is generally a stalk (that is, the stipe) having a flat blade (the lamina), often splitted into segments. The frond might be simple and undivided or it might be divided into a number of divisions (termed pinnae). New fronds are generated from the rhizome. They are tightly coiled into the spiral (termed as a fiddlehead or koru), and such slowly uncoil as they mature. Fronds encompass a dual function. They are there for photosynthesis however they are as well there for reproduction.
The spores grow within casings termed as sporangia. These are found on the base of fronds. Not each and every frond consists of sporangia beneath it. Fronds that encompass sporangia are termed as fertile fronds. In the enormous majority of ferns, the sporangia are found in clusters (termed as sori). These are the brown, black or orange patches which you observe on the base of fronds. If the sporangia break open, they liberate the spores.
Similar to all vascular plants, ferns encompass a life cycle often termed to as alternation of generations, characterized through a diploid sporophytic and a haploid gametophytic stage. Dissimilar the angiosperms and gymnosperms, in ferns the gametophyte is a free-living organism. The life cycle of a characteristic fern is as described:
a) A sporophyte (that is, diploid) stage generates haploid spores through meiosis;
b) A spore grows up through cell division into a gametophyte, which usually comprises of a photosynthetic prothallus, a short-lived and inconspicuous heart-shaped structure usually 2 to 5 millimeters broad, having a number of rhizoids (that is, a root-like hairs) growing beneath and the sex organs.
c) The gametophyte generates gametes (frequently both sperm and eggs on the similar prothallus) through mitosis.
d) A mobile, flagellate sperm fertilizes an egg which remains joined to the prothallus.
e) The fertilized egg is now a diploid zygote and grows up through mitosis into a sporophyte (that is, the usual 'fern' plant).
Reproduction in Ferns:
Spores build up within the sporangia; if they mature they are released and dispersed if sporangia dehisce.
The indusium dries up and shrinks;
The wall of sporangium dries out and tension forms in the annulus that curls back, flinging the spores out of the sporangium.
Beneath favorable conditions of moisture and temperature each and every spore germinates into a very minute, thin, heart-shaped green structure, termed as the Prothallus.
Margin of the prothallus is much thin and single-layered whereas the central part is moderately thick and of numerous layered.
Unicellular hairy Rhizoids nurture out from beneath the surface of prothallus and anchor the prothallus to the soil;
The prothallus is fragile and lacks a cuticle and is prone to desiccation, therefore it survives just in damp situations.
Economic and Biological significance of Ferns:
i) They are at times employed for decoration as ornamental plants.
ii) They are as well of evolutionary significance and make links among mosses and gymnosperms. They are the very first land plants having true roots.
iii) They are eaten by animals
iv) Fossil ferns contribute to the making of coal-beds, natural gas and petroleum products.
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