CYCAS 1.pdf

cycas

1. CYCAS
Systematic Position
Division: CYCADOPHYTA
Class: CYCADOPSIDA
Order: CYCADALES
Family: CYCADACEAE
Genus: CYCAS
(Greek word Kycas= Cocopalm)

2. Distribution & Occurrence
Includes 15 -20 Species
Occurs wild or cultivated in tropical and sub-tropical
regions
Common Indian Species:
Cycascircinalis
C. rumphii
C.beddomei
C.revoluta
C.siamensis
C.pectinata

3. GENERAL MORPHOLOGY
Plants are low and
palm-like, height 4-8
feet
Plant body consists of a
columnar aerieltrunk
with a crown of
pinnatelycompound
leaves at its top.

4. Roots –2 types
Normal tap roots
Positively geotropic
Grow deep into soil
Possess no root hairs
Function: fixation and
absorption
◼Coralloid roots
◼Arise from normal roots
nearthe ground surface
◼Infected with bacteria
,fungi and algae
◼Grow horizontally in the
soil become swollen at
tips
◼Divide repeatedly to
form bunches-greenish
or brownish
◼Coral like appearance

5. Stem
Thick, woody and unbranched
Tuberous when young but columnar erect and stout
at maturity
Aerial part remains covered by thick large
rhomboidal leaf bases
Larger leaf bases –foliage leaves
Smaller ones –scale leaves

6. Leaves –2 types
Foliage leaves / assimilatory
fronds
Green , large, pinnately
compound leaves with spiny
petiole and large strong rachis
Rachis bears many leaflets
Scaly leaves / Cataphylls
Dry , brown coloured
,somewhat triangular leaves
Present at the apex of the stem

7. Anatomy –Coralloid root
Anatomically Coralloid
roots resemble normal
roots except some
differences:
Secondary vascular tissue
is totally absent
Cortex is wider
Presence of a greenish algal
zone in the middle of the
cortex

8. Anatomy leaflet
Leaflet is thickly cutinized and leathery
Possesses all xerophyticcharacters
Sunken stomata and thickened hypodermis
present
Well developed palisade layer in mesophyll
Between the palisade and lower mesophyll
layers, there are transversely running long
colourless cells in 3-4 layers extending from
mid-rib to near leaf margin
These constitute the transfusion tissue
Mid rib bundle consists of a broad triangular
centripetal xylem and two small patches of
centrifugal xylem
Phloem abaxiallyplaced

9. Reproduction –Vegetative
Vegetative reproduction is
by means of bulbils
Develop in crevices of
scale leaves and leaf bases
at the basal part of an old
stem
Produces new plant on
detachment

10. Reproduction –Sexual
Strictly dioeciousplant
Male strobilus or cone
borne singly at the apex of
the trunk
Apical shoot apex utilized
in the development of
male cone, hence
branching sympodial
Cone shortly stalked &
large(upto50cm length or
more)
Cones or strobiliare
found at the apex of the
trunk

11. Numerous micro-sporophylls
spirally arranged around the
central axis
Each micro-sporophyllis
narrow below and broad
above terminating into
projection–the apophysis
Microsporangiaconfined to
abaxial(lower) surface
Usually present in sori–each
with 2-6 sporangia
They contain a large number
of haploid microspores
(pollengrains)

12. Pollination -Development of male
gametophyte after pollination
The pollen grains are carried by wind(Anemophily)
and caught by pollination drop secreted by ovule.
Pollination is direct.
The pollination drop is dehydrated and the pollen
grains are sucked in to the pollenchamber.
Pollen grains take rest for some time in the pollen
chamber

13. During the germination of pollen grain the exineis
ruptured and the inner intinecomes out in the form of a
tube like structure known as pollentube.
At this time the generative cell divides and forms a
larger,upperbody cell and smaller,lowerstalk cell.
The pollen tube acts as haustoriumto absorb food materials
from the nucellusbesides as sperm carrier.
During the germination of pollen grain the exineis ruptured and the inner intinecomes
out in the form of a tube like structure known as pollentube.
At this time the generative cell divides and forms a larger,upperbody cell and
smaller,lowerstalk cell.
The pollen tube acts as haustoriumto absorb food materials from the nucellusbesides as
sperm carrier.
The body cell divides and forms two naked,topshaped,motile,multiciliated
antherozoids.Thecilia are in 4–5spirals.
The male gametes of Cycasare 180–210μin size and largest in the plant kingdom.

14. Female Reproductive Structures
Female plant do not produce
definite cones
A whorl of spirally arranged
megasporophyllsarise
around the short apex
Each megasporophyll
resembles the foliage leaf and
approximately 10-23 cms.
long
Lower petiolarpart bears the
naked ovules on the margins

15. Ovule Structure
Ovules are orthotropous, sessile,
ovoid or spherical in shape and
unitegmic.
The thick integument is
differentiated in threelayers-
outer and inner fleshy layers,
middle stony
The integument remains fused
inside with nucellartissue except
at the position where it forms the
micropylaropening.
Ovule is well supplied with
vascular bundles.

16. Megasporangium
The megaspore develops in the nucellusby meiotic
division and goes on to form female gametophyte
tissue.
2-3 archegonia are formed in this haploid tissue
which is food laden.
Egg cell in the venterof archegonia,undergoes
fertilization by the motile spermatozoid forming
diploid zygote

17. Young Sporophyte–Embryo
Embryo development is meroblastic.
Pro embryo shows upper haustorialpart, middle
elongating suspensors and the basal meristematic
embryonalregion.

18. Seed
A mature embryo is straight and has a short hypocotyl.
Embryonalaxis has plumuleat one end and radicleat the other.
Radicleis covered by coleorhiza.
Number of cotyledons may be 2-3..
Nucellusis completely absorbed in the seed.
Mature seed is large 2.5–5cm wide and usually orange or red in
colour.
Germination is epigealtype

19. Germination of Seed (Seedling):
The seeds have no resting period and germinate
immediately if placed on moist soil.
The seed is large and longer than broad.
It absorbs water from the moist soil and the
coleorhizacomes first and the tip of the primary
root makes its way through the coleorhiza.
The major part of the cotyledons comes out of the
seed
The leaves begin to develop singly on the new plants
It has been observed that for a number of years only
one leaf is developed at a time.