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A Handbook of Biology
PTËRÏDØPHÝTËS
Primitive seedless vascular plants that have conspicuous
sporophytic plant body and inconspicuous gametophytes.
They include horsetails and ferns.
Used for medicinal purposes and as soil-binders. Frequently
grown as ornamentals.
Found in cool, damp, shady places though some may flourish
in sandy soil conditions.
In bryophytes, the dominant phase in the life cycle is the
gametophytic plant body. In pteridophytes, the main plant
body is a sporophyte which is differentiated into true root, stem
and leaves.
The leaves in pteridophytes are small (microphylls) as in
Selaginella or large (macrophylls) as in ferns.
The sporophytes bear sporangia that are subtended by leaf-
like appendages called sporophylls. In some cases sporophylls
may form distinct compact structures called strobili or cones
(Selaginella and Equisetum).
Sporangia produce spores by meiosis in spore mother cells.
The spores germinate to give rise to inconspicuous, small,
multicellular,
free-living,
mostly
photosynthetic
thalloid
gametophytes called prothallus.
The gametophytes bear male and female sex organs called
antheridia and archegonia respectively.
Water is needed for transfer of antherozoids (male gametes
from antheridia) to the mouth of archegonium. (NEET 2016,
AIPMT 2009)
Antherozoid fuses with the egg in the archegonium to form
zygote.
Zygote produces a multicellular well-differentiated sporophyte
(dominant phase of pteridophytes).
Most of the pteridophytes produce similar kinds of spores
(homosporous plants). Others produce two kinds of spores,
macro & micro spores. They are heterosporous. E.g. Selaginella
& Salvinia. (AIPMT 2008)
The megaspores & microspores germinate and give rise to
female and male gametophytes, respectively. The female
gametophytes are retained on the parent sporophytes for
variable periods. (AIPMT 2011)
Within female gametophytes, zygotes develop into young
embryos. This event is a precursor to the seed habit. It is
considered as an important step in evolution.