ORIGIN OF PTERIDOPHYTES PDF DOWNLOAD

Pteridophytes (Greek; pteron -feather) are called as vascular cryptogams Regarding origin of pteridophyta, scientists have proposed two different hypotheses. Occurrence and evolution of Pteridophytes with its origin and economic importance in Pteridophyta is a group of ancient plants. They formed the dominant part of. A pteridophyte is a vascular plant (with xylem and phloem) that disperses spores. Because . The Origin and Early Diversification of Land Plants: A Cladistic Study. Washington, D.C.: Smithsonian Institution Press. ISBN Pryer  ‎Taxonomy · ‎Ecology.


ORIGIN OF PTERIDOPHYTES PDF DOWNLOAD

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ORIGIN OF PTERIDOPHYTES PDF DOWNLOAD


Pteridophytes: Meaning, Origin and Economic Importance

The antherozoid and egg — of haploid chromosome number — fuse to form a diploid zygote, which is the mother cell of sporophytic generation. The zygote undergoes repeated divisions to form embryo.

Further development of embryo origin of pteridophytes into a well-developed sporophyte differentiated into roots, stem and leaves. According to the polarity, the embryo may be categorised into two types viz. In endoscopic embryo the shoot-forrping apical pole is directed downward i.

The basic life cycle pattern of pteridophytes shows a regular heteromorphic alternation of generations between a gametophyte sexual phase and a sporophyte asexual phase. The main plant body is sporophytic which origin of pteridophytes a dominant phase in the life cycle.

The gametophytic generation bears male and female sex organs viz.

Pteridophytes: Origin, Classification and Importance | Botany

The antherozoids male gamates produced in large numbers are motile, while the eggs female gametes are non-motile and are borne singly in archegonia. Fusion between an egg and an antherozoid results in the formation of a diploid 2n zygote.

Origin of pteridophytes homosporous member, spores germinate to produce monoecious origin of pteridophytes. In this case, the sex determination takes place at the time of formation of antheridium and archegonium Fig.

In heterosporous member, micro- and mega- spores, on germination, produce male and female gametophytes, respectively i.

Life Cycle of Pteridophytes: Origin of pteridophytes alternation of sporophyte 2n and gametophyte n generations in the life cycle is normally coordinated with a periodic doubling because of syngamy followed by a halving because of meiosis of the chromosome number.

Life forms of Pteridophyta, their origin and evolution.

In some ferns, the origin of pteridophytes develops from an unfertilised egg, a phenomenon termed as parthenogenesis i. A third deviation from the usual life cycle of pteridophyte is the phenomenon of apogamy.

The origin of pteridophytes of true roots, stem, leaves and vascular tissues thus have distinguished them from the preceding group i.

The pteridophytes resemble the Spermatophyta in having well- developed vascular tissues but differ from them in lacking flowers, fruits or seeds.

Stelar System in Pteridophytes: The name stele has been derived from the Greek word stele meaning column or pillar or set or stand. According to origin of pteridophytes the fundamental parts of a shoot are the cortex and the stele a central cylinder where origin of pteridophytes endodermis is the anatomical boundary between these two fundamental units.

How did the Pteridophytes Plants Originated? – Discussed!

In lycopsids, like Lycopodium and Selaginella, the stele of the axis and the leaf traces develop independently. The leaf traces are very small and superficially connected to the vascular cylinder of the stem Fig.

But in ferns e. It is considered as a composite structure consisting of both origin of pteridophytes stem and foliar leaf vascular components.

University Botany I : (Algae, Fungi, Bryophyta And Pteridophyta) - S.M. Reddy - Google книги

Types of Steles in Pteridophytes: It is characterised by the absence of central column of pith. Thus it is a non-meduMated stele, in its most simplest form it is merely origin of pteridophytes of a central strand of primary xylem surrounded by a cylinder of phloem.

From the phylogenetic as well as ontogenic standpoint the most primitive type of stele is the protostele.

ORIGIN OF PTERIDOPHYTES PDF DOWNLOAD

All other types of steles have been derived from it in the course of evolution. Protosteles are found in primitive psilophytes like Rhynia, Horneophyton and also in many living primitive vascular plants e. Different types of the protostele origin of pteridophytes in the pteridophytes are: The phloem, instead of forming a continuous ring, is situated in the form of small groups in between the radiating arms of the xylem e.

In this origin of pteridophytes of protostele, the xylem cylinder breaks into several separate plates Fig.