Introduction to botany | © punam kumar |
The vascular tissue of the axes is known as the stele. It mainly comprises the
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The various types of stele found in pteridophytes are protostele and siphonosteles.
Protostele is the simplest and most primitive type of stele. There is a solid core of
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by phloem followed by pericycle and the endodermis. Pith is absent. Three types of general variations are- haplostele,
actinostele, and plectostele
In siphonostele there is a central parenchymatous tissue-the pith, which is surrounded by the xylem, phloem,
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endodermis.
Siphonosteles are of two types - ectophloic siphonostele and amphiphloic siphonostele(solenostele).
Plants have two further variations on their life cycles. Plants that produce bisexual gametophytes (produces both sex organ on
same plant) have those gametophytes germinate from isospores (iso=same) that are about all the same size. This state is
referred to as
_ _ _ _ _ _ _ _ _ _ _ _ (or
isospory).
In heterospory plants produce separate male and female gametophytes .The male gametophytes produces sperm and is associated
with smaller or microspores. The female gametophyte is associated with the larger or megaspores.
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considered by botanists as a significant step toward the development of seed.
A fern, or Pteridophyte, is any one of a group of plants classified in the Division Pteridophyta, formerly known as
_ _ _ _ _ _ _ _ _ _ _ _ .Ferns are
seedless vascular plants and reproduces by spores and by alternating generations of separate spore producing plants
(sporophytes) and gamete producing plants (gametophytes).
A fern is a vascular plant that differs from the more primitive lycophytes in having true leaves (megaphylls) and from the more
advanced seed plants (gymnosperms and angiosperms) in lacking
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reproducing with spores.
Ferns first appear in the fossil record in the early-Carboniferous period. By the
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evidence of ferns related to several modern families appeared.
The "great fern radiation" occurred in the late-Cretaceous, when many modern families of ferns first appeared.