This is a part of the online class for the undergraduate Botany students

1. CYCAS
(Sago palm)
SYSTEMATIC POSITION
DIVISION- GYMNOSPERMAE
CLASS- CYCADOPSIDA
ORDER- CYCADALES
FAMILY- CYCADACEAE
GENUS- CYCAS
Classification
An old Cycas plant
Male plant
Female plant
2N =22
Dr P B Mallikharjuna
GFGC Yelahanka
9th,16th, 23rd & 26th June 2021
1

2. GEOGRAPHICAL DISTRIBUTION
 Cycas, with about 16 species (Willis, 1951) is the most
widely distributed genus in the Eastern Hemisphere.
 It is an oriental genus, found as wild or cultivated in the
tropical and sub- tropical regions of the world.
 The species are usually distributed in the southern parts
of Japan, India, China, the Islands of Indian and Pacific
oceans and the northern part of Australia.
 A few species grow as far as Madagascar, Mauritius and
East coast of Africa.
 Cycas revoluta, a native of China and Japan, is the
commonest and the most widely cultivated cycads and is
grown throughout the world for its ornamental value.
2

3.  C. medagascaransis is found in Madagascar and Africa.
 The genus Cycas is represented by six species (Raizada and
Sahni, 1958) in India and mainly distributed in the north
east i.e., East Bengal, Orissa, plains of Assam , Nepal and
Sikkim; and in south - Mysore, Madras and Malabar.
 C. pectinata , C. siamensis, C. circinalis, C. rumphii, C.
revoluta and C. beddomei. Out of six, the last four species
are quite common and are found in wild state in the
country.
 C. revoluta is by far the most commonly cultivated species
of Indian gardens , C. siamensis, a native of Siam and Burma,
is also sometimes cultivated.
 In India, Cycas beddomi grows widely in Tirumala Hills and
C. rhumpii in Andaman & Nicobar Islands and also in the
neighbouring countries like Burma and Sri Lanka
 Recently a new species Cycas swamyi has been reported
from Karnataka (2008) 3

4. INDIAN SPECIES OF CYCAS
C. pectinata
C. siamensis
C. circinalis
C. beddomei
C. revoluta
C. rumphii
C. circinalis
C. revoluta
C. sowmyi 4

5. THE PLANT BODY :
EXTERNAL MORPHOLOGY
 The sporophytic plant: slow growing, long-
lived, evergreen and woody genus.
• It has unbranched columnar stem with crown
of pinnately compound leaves at the top and
resembles to a palm or tree fern in its
external appearance
• Fully grown plant of most of the species
normally ranges from 2 to 5 meters in height,
though some species may attain a height of
about 13 to 20 meters or more.
• C. media, an Australian species, is perhaps
the often reaching a
height of 20 meters.
• Cycas morphologically looks like a palm
(monocot) tree and anatomically like a dicot.
Cycas old plant
5

6. Root: Tap root system
• Primary root is a short-lived tap root which later on is
replaced by adventitious roots arising from the stem
tissue.
• Well developed primary root is long and sometimes
almost as thick as the stem, and in seedling stage
root is much larger than the stem.
• Most of lateral branches of primary root, that are
commonly known as normal roots, penetrate the soil,
and anchor the plant.
• The roots are associated with ectomycorrhizae
6

7. CORALLOID ROOTS
• Some of the roots, which develop near
the surface or above the ground, get
infected with certain algae, bacteria
and fungi already present in the soil
surrounding the root system called
coralloid roots.
• These roots grow at first horizontally
and then vertically in the soil and
become swollen at their tips due to
entry above mentioned micro-
organisms.
• They behave like negatively geotropic
structures come out in the air above
the soil surface and branch
dichotomously to form greenish brown
coral like mass and, therefore, are
named as coralloid roots . 7

8. CYCAS - STEM
• The stem is arborescent, erect,
stout, columnar and usually
unbranched.
• Trees may give out branches as a
result of injury or after they have
reached a certain age.
• The stem when young is tuberous,
short and subterranean. Most part
of the stem is covered with a
number of large (foliage leaves) and
small (scale) leaves in male plants
and scale leaves and
megasporophylls in female plants)
rhomboidal leaf bases.
• This hard armor of woody leaf bases
that persists for many years around
the stem is said to protect the stem
and can be used as an index of the
age of the plant.
8

9. • A crown of spirally arranged leaves
present around the stem apex
makes the Cycas look like a palm or
a tree fern.
• It bears the assimilatory foliage
leaves and brown scale leaves
arranged in alternating whorls.
• There are two types of leaves: large
green foliage leaves. Foliage leaves
are developed in the form of a
single crown under the cover of
armor of scale leaves each year.
• Young foliage leaves push aside the
scale leaves and begin to come out
with a rapid growth till they reach
full size in a few days.
CYCAS - LEAF
Pinnately compound leaves
9

10. • The young crown with
can easily be distinguished from the fully
expanded old crown.
• The number of leaves upto 100 in old
plants. Foliage leaves are produced in large
numbers and are pinnately compound,
showy, fairly large 1 to 3 meters, very
thick and leathery.
• They are attached to the stem by
transversely expanded rhomboidal leaf
bases. They possess a long or short petiole
and a long stout rachis.
• Petiole bears two rows of short and stiff
spines near its base.
• These gradually become transformed into
leaflets (pinnae) towards the distal end of
the leaf.
• In very young leaves rachis may be
circinate with circinately coiled leaflets like
those of ferns. 10

11. (II) SCALE LEAVES.
• Scale leaves are small, rough, dry, and
triangular and thickly covered structures
with brown hairs.
• Young stem apex is sheathed with such
scale leaves.
• They bear well developed bases each of
which tapers into a short, narrow and
broadly triangular apical portion.
• Apices of the scale leaves are spirally
twisted against each other.
• They look like the cords of a rope
enclosing in them young stem apex and
other young structures.
• Thus they Serve to protect the other
organs when young.
• Scale leaf bases are also persistent and
form part of the armor of the old stems.
11

12. Cycas - Anatomy
• The root and the coralloid root anatomy.
• The Stem primary growth and the secondary growth
• The Leaf anatomy – The Rachis and the Leaflet structures
12

13. ANATOMY OF THE ROOT
Two types of roots are found in Cycas.
1. Normal root:
 The Internal structure of normal root of Cycas
resembles with that of a dicotyledonous root.
 Epiblema is the single layered outermost
covering layer with thin walls, that gives out
root hairs
 Cortex is the middle zone in between
epiblema and vascular cylinder. It consists of
thin-walled parenchymatous cells rich in
starch.
 The cortex contains a large number of
mucilage canals which are bounded by
epithelial layer or secretary cells.
 Sometimes abundant air spaces and
interspersed dark brown tannin cells are also
seen.
 Single layered endodermis is provided with
the thickening of casparian strips..
13

14.  The thin-walled multilayered cells of
periycle contain abundant starch grains.
 The stele exhibits diarch to tetrarch and
rarely polyarch condition
 Each vascular bundle shows radial
arrangement of xylem and phloem, Xylem
and phloem alternate to each other.
 Protoxylem consists of trachcieds with
spiral thickenings and metaxylem with
scalariform and pitted thickenings.
 The centre of the root is occupied
completely by metaxylem or metaxylem
with interspersed parenchymatous cells.
 At an early stage phloem consists of sieve
tubes and phloem parenchyma but in
older parts also with bast fibers.
 Pith is reduced or completely absent.
Root Anatomy
14

15. SECONDARY GROWTH IN CYCAS ROOT
 Follows the same pattern as seen in dicot roots although starts
quite early.
 Normal secondary growth takes place as a result of Cambium
formation of cambial arcs along the inner edge of the phloem
strands.
 These soon cut of manoxylic secondary wood similar to the
stem.
 The primary phloem, as a result of formation of xylem rays, gets
crushed.
 A pair of cambial arcs, forming a continuous cylinder of
secondary vascular tissue, goes on adding secondary tissues.
 Coincidently a distinct phellogen (cork cambium) layer appears
in the cortex.
 It cuts off phelloderm (secondary cortex) on its inner and phellem
(cork) on its outer side with lenticels.
15

16. 16

17. 2. CORALLOID ROOT ANATOMY
 Internal structure of the coralloid
roots is similar to that of normal
roots but they differ from the
normal roots for not having
secondary growth, and the cortex is
differentiated into three distinct
zones:
 the outer cortex composed of
compactly arranged polygonal
parenchymatous cells.
The inner cortex is of thin walled
parenchymatous and
The middle cortex forming the algal
zone
17

18.  Algal zone, which is usually
one cell wide, consists of loosely
connected thin walled and radially
elongated cells both with
abundant large intercellular and
intracellular spaces.
These are occupied by certain
algae (Anabaena cycadeae,
Nostoc punctiforme, Oscillatoria
and diatoms), some fungi and a
few bacteria (Pseudomonas and
Azotobacter).
Each cell present in the algal
zone contains a single nucleus
and cytoplasm.
A portion is magnified
TS of Coralloid root
18

19. ANATOMY OF CYCAS STEM
 The stem anatomy of Cycas possess both the primary growth and the normal
secondary growth which resembles the dicot stem. However it differs for the
lack of some cells both in the xylem and phloem tissues
 In a transverse section, stem assumes an irregular outline due to the presence
of numerous leaf bases.
Primary growth:
 Epidermis: the outermost layer, on account of the presence of large number of
persistent leaf bases appears incomplete and ruptured.
 Cortex : a multilayered middle zone occupies greater part in between the
epidermis and vascular cylinder.
 Cortex consists of thin walled parenchymatous cells with abundant
starch.(Hence called Sago palm)
 Numerous mucilage ducts, calcium oxalate crystals, mucilage canals and
leaf traces can also be seen in this region. Two types of leaf trace present
viz., a pair of Girdle leaf traces and the radial leaf traces are present.
 The cortex communicates with the pith through more or less broad
medullary rays.
 Endodermis and pericycle are not distinct.
19

20. LEAF BASES
20

21.  Vascular cylinder is Eustelic occupies
comparatively smaller region of the stem
appears like the dicot stele.
 The vascular bundles are narrow,
radially elongated, collateral, conjoint,
open and endarch.
 They are small in size and more in
number, and are closely arranged in a
ring.
 Primary phloem elements, consisting
of sieve tubes and phloem
parenchyma and lacking companion
cells, but sieve tubes are associated
with albuminous cells.
 Short-lived primary cambium is
represented by a thin strip of
parenchymatous cells between the
primary xylem and primary phloem.
21

22.  Primary xylem consists of only trachcieds which show spiral
thickenings in protoxylem and scalariform thickenings in the
metaxylem often with bordered pits.
 A large parenchymatous cells rich in starch present in the medulla or
pith region and it contains a large number of mucilage canals.
 A striking anatomical feature of Cycas is the girdling of the stem. It is
caused by the large number of leaf traces.
 These are small and endarch of the stem, pseudomesarch as they enter
the leaf due to the formation of centripetal xylem and exarch at the
extreme terminal part of the rachis.
 For each leaf there are usually four traces of which two are main traces
girdle trace bundles while the other two are direct traces or radial
trace bundles.
22

23.  They pass out of the ring through a
gap formed by the splitting of the
vascular cylinder. Main trace bundle
first passes obliquely through the
cortex.
 Then it divides into two halves each
half running round in opposite
directions in the outer cortex where
they rise and meet at the base of the
leaf and finally bend sharply into the
petiole.
 Because these trace girdles run round
the central cylinder in the cortex, they
are given the name girdle-traces".
 These in turn bifurcate and each half
branches freely so as to produce a
complex system of anatomizing
bundles.
LS of the Cycas
stem tip
23

24. SECONDARY GROWTH
 The secondary growth occurs in the Cycas stem due to the formation
of vascular cambium in the stelar region and the cork cambium in the
cortical region as in the dicot stem.
 Secondary growth in the stem begins quite early.
 At first, it takes place by the activity of inter fascicular and primary
intra-fascicular cambia resulting, the formation of vascular cambial
ring.
 The cambial ring that cuts of secondary xylem on the inner and
secondary phloem on the outer side.
 Parenchyma cells and narrow uniformly parenchymatous secondary
medulary rays composed of cells rich in starch found distributed in
the secondary xylem are sometimes also cut off by the cambium on
the inner side. Secondary phloem comprises of fibres and sieve cells.
 Elongated bordered pits in the cell wall of metaxylem tracheids.
 Growth rings of any kind have not been observed in the wood.
 Occurrence of about 8 to 12 bordered pits in the xylem tracheids can
be marked by their presence in two or three series, sometimes
alternate or pressed. 24

25. Cycas stem TS with Secondary growth
Cycas stem is with the manoxylic,
nonporous, polyxylic wood anatomy
25

26. 26

27.  After the primary cambium ceases to be active, secondary cambia
develop in the cortex or pericycle and produce cortical cylinders.
 As a result of the diminishing sequence in the activity of successive
cambial rings, the vascular rings exhibit a gradual narrowing from
the first vascular ring to the outermost ring of the vascular cylinder.
 Thus the innermost vascular ring is almost as thick as primary
vascular ring and the outermost may be thinnest.
 The concentric rings are separated from each other by a few layers
of parenchymatous cells. Secondary rings are composed of the
same elements as found in the primary rings of vascular bundles.
 Vascular bundles of secondary rings, which differ from the leaf
trace bundles on account of the absence of Protoxylem, are
traversed by broad medullary rays, leaf traces, mucilage canals and
cortical bundles running throughout from the first ring to the
cortex.
 Occasionally, the arcs of inverted vascular bundles may also occur
between the normal rings. Thus very old stem shows polycyclic
condition. 27

28. RLS through wood
HLS of wood
Bordered pits
Sieve
tube
Cycas stem wood anatomy
Tracheid with
Bordered pit
28

29. ANATOMY OF RACHIS
 In a T/S rachis may appear biconvex, cylindrical or flattened depending
upon the region. A pair of depressions of arms on either side, passing into
the leaflets.
 Thick-walled and single layered epidermis with rectangular cells is
covered with cuticle. Stomata are irregularly arranged and sunken.
 Ground tissues are differentiated into three defined zones.
 The hypodermal region is differentiated into outer green
chlorenchymatous and inner thick walled compact sclerenchymatous.
 A narrow zone of chlorenchymatous cells occurs just below the
epidermis
 A sclerenchymatous zone consists of 2-3 cell layers thick in adaxial surface
and poorly developed near the depressions
29

30. Ground plan of Rachis TS
A vascular bundle
30

31.  A number of mucilage canals and a few cells with star-shaped
Crystals of calcium oxalate also occur in this zone.
 A varying number of vascular bundles are found embedded in
the parenchymatous tissue.
 The vascular bundles which are more or less oval are conjoint,
collateral and open and are arranged in the form of Greek letter
omega (u) or horse shoe.
 The arrangement and the number of vascular bundles,
however, variable in the different parts of one and the same
rachis.
 Each vascular bundle is enclosed by a thick-walled
sclerenchymatous bundle sheath.
31

32.  Pericycle is one to several layered thick encloses xylem, phloem, a thin
strip of inactive cambium and parenchyma.
 vascular bundles are characterized by the presence of two types of
xylems arranged in two patches of endarch (centrifugal) xylem and
exarch (centripetal xylem) and are called "pseudomesarch" or
"diploxylic"
 Phloem occurs by the side of the centrifugal xylem.
 A thin strip of cambium occurs in between the phloem and xylem.
 Bundles present at the two open ends, as apparent in their omega shaped
arrangement, pass out and enter the two pinnae. The continuous entry of
the vascular bundles in the pinnae, from base to the apex of the rachis,
gradually reduces their number. Ultimately terminal bundles too enter
one by one in the terminal pinnae of the leaf. 32

33. ANATOMY OF CYCAS LEAFLET
Whole mount/section
A portion is magnified
33

34. • In a vertical section leaflets or pinnae reveal xerophytes
characters. (presence of cuticle, hypodermis, sunken stomata,
bundle sheath )
• The epidermis is single layered with thick walled cells.
• It is continuous on the upper side and is interrupted on the lower
side with minute pits at the bottom of which lie sunken stomata (
haplocheilic type)
• Each stomata opens outside into "epistomatal cavity and inside
into a "hypostomatal chamber".
• Each stoma consists of two guard cells that are surrounded by a
pair of papillated or projected subsidiary or buffer cells that
regulate the opening and closing of the stomatal aperture. 34

35. • Internal to the upper and lower epidermis lies single layered thick
sclerenymatous hypodermis. While in the midrib region it is two or more
layered thick.
• Besides providing mechanical strength, the hypodermis acts as a heat
screen and protects the leaflets from overheating and excessive
transpiration.
• Next to hypodermis is a zone of chlorophyllous mesophyll cells.
• The mesophyll is differentiated into vertically elongated palisade tissue
situated towards upper side and loosely arranged spongy parenchyma
tissue towards the Side, Palisade acts as an assimilatory tissue and
consists of single layer of linearly arranged chloroplasts.
35

36. • Spongy parenchyma, an assimilatory and aerating zone lies above the
lower epidermis and consists of the palisade layer and spongy
parenchyma occurs a three or four thick transfusion tissue composed of
long, colorless parenchyma cells .
• This tissue is connected with centripetal xylem, the bundle sheath and
runs laterally from the middle to the edges of the leaflet.
36

37. •The cell walls of this tissue are provided with reticulate or bordered pitted
thickenings. A few tracheidal cells, looking like the colorless lignified tracheids,
are also found distributed in between the mesophyll cells on either side of the
midrib.
• They are provided with bordered pits on their radial walls.
• These constitute the primary transfusion tissue and appear close to vascular
bundle.
• The transfusion cells are arranged at right angles to the axis of the leaf and
constitute the so called radial parenchyma, secondary transfusion tissue,
hydrosterom or accessory transfusion tissue.
37

38. • Some of the parenchymatous cells around the
stele are provided with star shaped crystals of
calcium oxalate and are called
sphaeroraphides.
• In the midrib region, there is a single large
vascular bundle surrounded by a jacket of
thick-walled cells. Phloem lies towards the
lower surface of the leaf. Protoxylem is
diploxylic or pseudomesarch.
• The centripetal Xylem is directed towards the
upper surface of the leaf and the centrifugal
xylem towards the lower leaf surface.
Centrifugal xylem consists of a few tracheidal
elements.
A single vascular bundle
38

39. Cycas – Sexual Reproduction
The male cone structure &
The female megasporophyll and ovule structures
The sexual reproduction in Cycas occurs after attaining
certain age i.e.. about 5 - 10 years old. Bulbils are rarely
produced as the vegetative propagules in some species.
39

40. Sexual Reproduction
• Sexual reproduction is the most common type of
reproduction in Cycas.
• It takes place by the formation the large or conspicuous
reproductive structures called the male cones and the
female megasporophylls.
• The plants of Cycas are heterosporous and invariably
dioecious, i.e. male and female reproductive organs occur
on separate individuals.
40

41. Male sex organs of Cycas
Male plant with a single cone
41

42. Male cone/ strobilus: A male cone is an oval or
conical large structure with numerous spirally arranged
microsporophylls, which almost perpendicularly attached to
the cone axis.
 The new stem apex appears terminal and develops fresh
crowns of foliage leaves and scale leaves. Another male
cone develops at the tip of such lateral branch.
 The male strobilus is shortly stalked, long, compact and
fusiform or oval structure surrounded by a crown of young
leaves.
 Mature strobili appear woody in texture and are about 20 to
60 cm long.
 These sometimes attain length of about 80 cm as reported
in some plants of C. circinalis, 42

43. Male
cone
Microsporophyll
Central axis
Sorus of microsporangia
A microsporophyll with sori
Cycas male reproductive structures
43

44.  The male strobilus consists of a number of
microsporophylls (stamens) closely arranged in spirals
acropetally on the central cone axis.
 In a surface view microsporophylls appear to be arranged
in vertical rows.
 The young microsporophylls are soft and fleshy,
become hard and woody at Apophysis
 They are small towards the base and the apex of the
strobilus and attain their maximum length (30 to 35 mm
long) in the middle.
 Some of the microsporophylls situated at the extreme
top and at the base may be sterile.
44

45.  Microsporophyll: Each microsporophyll arises as a
small outgrowth on the central cone axis and appears as
a wedge-shaped more or less triangular and flattened
structure about 3 to 3.5 cm in length at maturity.
 The basal part of each microsporophyll, arising at right
angle to the central axis, is narrow and 'sterile.
 It gradually becomes broader, and finally terminates into
an expanded sterile disc with a short upward projection,
the apophysis that overlaps other microsporophylls at
higher level. In between, the basal part of the
microsporophyll and apophysis lies the fertile part.
45

46.  Microsporangia (pollen sacs) are borne on the abaxial
(lower) surface of the microsporophyll.
 They occur in quite large number (about 700 in C. circinalis
and 1,000 in C. revoluta) and are arranged in definite sori in
two depressed zones on either side of a median ridge.
 The number of the sporangia in each sorus varies from 2 to 6.
Unicellular or bicelled hairs occur intermixed with sporangia.
 The development of the microsporangium is of eusporangiate
type.
46

47. Mature microsporangium:
 A fully mature microsporangium looks like a short stalked
oval sac.
 At maturity microsporangium possess a single layered
wall, enclosing within it the spores.
 The tapetum and outer wall cells get disintegrated.
 Dehiscence of microsporangia: The ripen
microsporangia dehisce by longitudinal slits along the
thickened cells on the outermost layer of the wall.
 These cells loose water and shrink. Because of elongation
of central' cone axis, microsporophylls get separated and
expose the boat shaped open microsporangia.
47

48.  At this stage, the microsporophylls as well as central
axis of the male cone become hard due to the loss of
the turgidity and drying of resins.
 When dry, resin becomes inelastic and hard. Since the
ripening depends largely on drying, the youngest
microsporophyll present at the top of the strobilus and
farthest from water supply, ripen their pollen grains
first.
 Consequently, shedding of the pollen grains starts
from the top most sporophylls and proceeds towards
the base.
48

49. LS of microsporangium
49

50. Cycas - Female Reproductive structures
Megasporophylls.
 Cycas is unique in that there does not posses female cone/ strobilus,
The megasporophylls occur in close spirals around the stem apex of
the female plant.
 They are loosely arranged in acropetally succession and give an
appearance of a rosette.
 The apical meristem is left unaffected and continues to grow
throughout the plant life and forms the future leaves and sporophylls.
 The development of the megasporophylls starts soon after the plant is
somewhat mature.
 Usually the megasporophylls are formed once a year and occupy their
position in between successive whorls of foliage resemble closely with
the foliage leaves and arise from the places where, under leaves.
50

51.  Megasporophylls at first bend inwards and cover the growing
point but soon with the elongation of the stem they get pushed
away and assume a horizontal or drooping position.
 Each megasporophyll is differentiated into three, more or-less
distinct parts:
I. A proximal short or long stalk like axis,
II. A middle portion bearing two rows of opposite and
alternately arranged ovules, and
III. A distal more or less expanded, dorsoventrally flattened
sterile portion of varying shapes.
 In most cases, megasporophylls are covered with yellow or
brown wooly hairs called ramanta e.g. C. revoluta.
51

52. The largest ovule is in the Cycas thourasii (7cm height) followed by
C. circinalis (6 cm) in the entire Plant kingdom
52

53. C. swamyi
Variation in the structure of megasporophylls and ovules in the Indian
Cycas species
53

54. Megasporangium / Ovule: The ovules of Cycas are large,
orthotropous, shortly stalked, unitegmic and perhaps the largest
in size. The number of ovules per megasporophyll varies usually
from 2 to 12 (1 to 6 on either side).
Structure of the ovule: A mature ovule of Cycas shows
the following structures.
 The ovule is of considerable size (about 6 cm in length and 4
cm in diameter) and can be seen by naked eyes.
 When young, it is green and covered with hairs but on
maturity it appears orange or red and loses the hairs.
 Each ovule is an oval or spherical structure with a central
mass of parenchymatous tissue called nucellus.
54

55.  The nucellus is surrounded by a single, about 1 cm thick
integument which is differentiated into three layers;
(i) Outer fleshy layer (outer sarcotesta),
(ii) Middle stony layer (middle sclerotesta) and
(iii) Inner fleshy layer (inner sarcotesta)
Egg
55

56.  Integument protects the megasporangium.
 It gets transformed into Outer Fleshy layer, Middle Stony layer
and Inner Fleshy layer,
 Middle layer possesses 2 to 3 ridges. Inner fleshy layer is
composed of parenchymatous cells except at the apex, It is
consumed during the development of the ovule and persists
as a thin papery layer.
 Further, it is having the pollen chamber, Archegonia, Nucellus ,
Female gametophyte, Vascular strands ,
 Integument remains in close contact with the nucellus except
at the apical region where it forms a long micropyle.
56

57.  The apical portion of the nucellus forms the nucellar beak
that forces its ways into the micropyle.
 In the centre of the beak and below the cells of the nucellus
break down and form the pollen chamber
 The ovule is supplied with a pair of vascular bundles at the
base.
 One of the branch of each vascular bundle enters into the
outer fleshy and the other into inner fleshy layer.
 After the act of pollination ovule gets considerably
enlarged.
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58. THE GAMETOPHYTES (Male & Female):
 Cycas is a heterosporous plant, i.e. bearing microspores (pollen
grains) and megaspores (embryo sacs).
 The development of the male and female gametophytes takes place
from microspores and megaspores respectively.
 Both microspore and megaspore mother cells represent the last
stages of the sporophytic generation.
 They divide meiotically while still present within the microsporangia
and megasporangia, respectively.
 Microsporangium produces a large number of functional
microspores, while the megasporangium produces only 3 to 4
megaspores, of which only basal one matures to form functional
megaspore and others degenerate.
 Microspores and megaspores represent the first stages of
gametophytic generation. 58

59.  Male Gametophyte: The microspore is the initial stage or unit of
male gametophyte.
 It is a unicelled , uninucleate and haploid structure.
 It has longitudinal slit. Each microspore is protected by two walls:
(i) Exine - the outer thick wall and
(ii) Intine - the inner thin wall.
 The microspore is subjected two asymmetric mitotic cell
divisions and thereby produce 3-celled ,haploid male
gametophyte or pollen grain.
 It possess a vegetative cell and two flagellate , motile sperms or
antherozoids .
 The Cycas male sperms are the largest gametes (200 µm) in the
plant kingdom
59

60. Pollen grain
Microspore
Metamorphosis
Antherozoid
60

61. 61

62.  Female Gametophyte: The female gametophyte is the
Archegonium which is a haploid , flask shaped and
multicellular structure. Further, it contains a pair of neck
cells and an egg cell with a large nucleus (500 µm).
 2-8 archegonia are present in an ovule surrounded by
endosperm.
 Archegonium is developed from the functional
megaspore due to meiosis of megaspore mother cell
(Megasporogenesis).
 The megaspore mother cell is derived from the nucellus.
 Some of these cells are also metamorphosed into the
haploid and nutritive tissue called Endosperm.
62

63.  Pollination: Wind pollination, but rarely insect pollination.
 The pollen grains may deposit into the pollen chamber of
the ovule.
 Rests for few months and germinate later
 Fertilization: Siphanogamous type or zoodiogamous type.
 The pollen grain germinates and produce a long pollen
tube from the vegetative cell and two ciliate-motile
gametes (antherozoids).
 The nucleus of the functional male gamete is sucked by
the archegonium , where it fuses with the large egg
nucleus and produces a diploid zygote.
 Seed : is the fertilized ovule and the matured seed is fleshy,
red, orange or brown in colour. It contains a dicotyledon
embryo and other tissues
63

64. Pollen tube
Antherozoid
Embryo
Pollen
Diagramatic
life cycle of
Cycas
64