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-Definition.!* : gymnospern are group of vascular
-cycads.!*
was much more extensive than at
-conifers.!* :appeared first toward the end of
plants.
present. In fact, gymnosperms were dominant in
the Late Carboniferous epoch [320 to 286
the Mesozoic.
Paleozoic seed ferns resembled
million years ago]. Some of the earliest
-Discovery.!* : In 1825 the scotish botanist Robert
some progymnosperms in that they were small
conifers [class Cordaitopsida] were trees
Brown
trees with fernlike leaves ,There has been one
with long, strap-shaped leaves. Trunks were
report of a pollination droplet in a Carboniferous
similar to those of extant conifers, with
pteridosperm ovule and a report of a pollen tube
dense, compact wood; small thick-walled
-Information.about.gynospern.!* : the seeds of many
emerging from a pollen grain in the micropyle of a
tracheids;
gymnospern are borne in cons and are not visible , this
seed-fern ovule, suggesting that transport of the
Reproductive axes were slender, bearing
are not like fruits. Some of the division of gymnospern
sperm through a pollen tube was in existence as
narrow bracts in the axils of which were
are not closete releated to others, having been
far back as the Paleozoic. It is generally conceded
small, budlike shoots with helically arranged
distintict groups for hundres million of years.
that from the pteridosperms arose members of the
scales. By the late Paleozoic there came into
division Cycadophyta. The first cycads appeared in
existence another group of extinct conifers,
the
the Voltziales ,
distinguished gymnospern from other major
group of seed plants.
General.features.!*
Permian
period
,Other
Permian
and
narrow
vascular
rays.
Reproductive axes were
megasporophylls, from China, are more like those
generally homologous with those of the
-Diversity.size.and.structure.!*:Among the gymnosp-
of Cycas. Cycad remains, especially leaves, are
Cordaitales, but they were more compact.
erms are plants with stems that may barely project
abundant in Mesozoic rocks. For this reason
Reproductive organs of seed ferns were
above the ground and others that develop into the
paleobotanists often refer to the Mesozoic era as
borne upon the foliage; single ovules and
largest of trees. Cycads resemble palm trees, with
the "age of cycads." The earliest well-known
seeds were borne in place of pinnae, while
fleshy
cycads
stems,
male organs often occurred as compound
sometimes branched, with leaves not borne close
pollen organs composed of partially or wholly
-distribution.and.abundance.!* : gymnosperms have
together, unlike the situation in extant cycads in
united
been gradually displaced by the more recently evolved
which leaves are densely crowded at the apex of
gymnosperms, the ovule consisted of one
angiosperms, they are still successful in many parts of
the plant.
megasporangium .It is generally conceded
stems and leathery, feat herlike leaves.
appear
to
have
had
slender
the world and occupy large areas of the Earth's
surface,
microsporangia.
As
in
other
that from the pteridosperms arose members
Gymnosperms that occupy areas of the
-exant cycads : Extant cycads are now limited in
world with severe climatic conditions are adapted to
geographic distribution to the warmer parts of the
conserving water; leaves are covered with a heavy,
earth.
waxy cuticle, and pores.
Mesozoic was another group of gymnosperms, the
Coexisting with the cycads during the
cycadeoids,Although they are superficially similar
in habit to the cycads.
of the division Cycadophyta.