Gymnosperms Gymno naked sperma seed include simpler and primitive plants They are characterised by the presence of naked ovules borne unprotected on the surface of the megasporophylls ID: 755854
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Slide1
GYMNOSPERMSSlide2
INTRODUCTION
Gymnosperms (
Gymno
: naked,
sperma
= seed
) include simpler and primitive
plants.
They are
characterised
by the presence of
naked ovules
, borne unprotected on the surface of the
megasporophylls
.
Gymnosperms are sometimes called as
phanerogams
without ovary
.Slide3
GENERAL CHARACTERISTICS
Most
of the living gymnosperms are evergreen trees or shrubs with
xerophytic
adaptation.
The main plant body is
sporophytic
and is differentiated into root, stem and leaves
.
The stem is usually erect, profusely branched (
Unbranched
in
Cycas
) and woody
. Sometimes
, as in
Zamia
, it is
tuberous.
Presence
of
leaf scars
on the stem is a characteristic feature of gymnosperms.Slide4
GENERAL CHARACTERISTICS
The
plant possess well developed
tap root
system.
Roots
of some have
symbiotic relationship with blue green algae (Coralloid roots of Cycas) or fungi (e.g. mycorrhizal roots of Pinus).Slide5
GENERAL CHARACTERISTICS
CYCAS PINUS
ZAMIA Slide6
LEAVES
The leaves are usually
dimorphic
.
The foliage leaves are
green, simple, needle shaped or
pinnately
compound.Scaly leaves are usually minute and deciduous.The leaves are well adapted to withstand extremes of temperature, humidity and wind due to following features. -Needle like leaves reduces surface area.
-Thick cuticle.
-Sunken stomata.Slide7
LEAVESSlide8
REPRODUCTION
Main plant body is
sporophyte
and
heterosporous
. It
produces
haploid microspores and megaspores.The spores are produced in sporangia that are born on sporophyll.The sporophylls are arranged spirally along an axis forming compact strobili
or cones
.
The male and female cones or
strobili
may be borne on the
same tree (
Pinus
)
or on
different trees(
Cycas
).
Strobili
bearing
microsporophylls
and
microsporangia
are called male
strobili
or male cone.Slide9
STROBILISlide10
REPRODUCTION
MALE
CONE (STAMINATE CONE)
Male cones are usually short-lived.
Microsporangia
develop on the
abaxial
side of the microsporophylls. The number of sporangia persporophyll varies from two to many.Microspores develops into a male gametophyte generation which is much reduced and is confined to only a limited number of cells..This reduced gametophyte is called a pollen grain.Development of pollen grains takes place within the micrsporangia.
FEMALE
CONE (OVULATE CONE)
The
cones bearing
megasporophyll
with
megasporangia
(ovules) are called as female cone.
In
megasporangia
, the mega spore mother cell divides
meiotically
to form four haploid megaspores.
One of the megaspore develops into a
multicellular
female
gamerophyte
that bears two or more archegonia.Slide11
REPRODUCTIONSlide12
REPRODUCTION
Strobili
bearing
microsporophylls
and
microsporangia
are called male
strobili or male cone.The pollen are released from the microsporangium and are carried with air current to the ovules. After fertilization, zygote develops into embryo and ovules into seeds. The seeds are naked.Slide13
LIFE CYCLE OF
PINUSSlide14
ECONOMIC IMPORTANCE
Edible
seeds
Ornamental
Timber
Paper
Drug- Ephedrine
Fibre boardEssential oilResins- Turpentine