Cycas-Morphology ,Distribution and Reproduction

                                                         Cycas      

Distribution of Cycas:-

It is the sole genus of the family Cycadaceae, that is delineated in the Asian nation. it's got regarding fifteen species (Sporne, 1965), twenty species (Willis, 1966) that area unit cosmopolitan in japan also as occident from Madagascar, jap the coast of the continent to Japan and Australia touching China and the Asian nation.

Cycas Revoluta

In our country a number of  the species-area the unit found growing profusely within the South Andaman and Nicobar islands, Madras, Mysore, Malabar and in North East in the geographical area, Assam, Kingdom of Nepal and geographic area. a number of of the species also are found in Asian nation and Ceylon.

 Male Cone -Cycas

Morphology or External Feature of gymnosperm genus:-

Cycas Plant could be a well-developed tree. It grows in xerophytic condition and is slow-growing plant reaching a height of 3-5 meters in regarding one hundred years .It has true root, stem, and Leaves.

Root:-

It has Tap root system. The root area unit well developed, branched, and fix into the soil. Some branches of the secondary root are apogeotropic in order that they come out from the soil.

They become related to Blue chlorophytes like blue-green algae and Anabaena .they are continual branched like corals thus referred to as Corraloid roots.

Stem:-

The Stem is stout and stay underground for several years . When arial ,it is branchless and armoured with thick persistant leaf bases .leaf happens as a crown within the higher half .

Female half contain 3 kinds of leaves : Scaly leaves,Foliage leaves and sporophyll kind Leaves.

Bulbils is seen within the lower a part of Stem in cycas revolute.

Leaves :-

Leaves area unit polymorphism kind

The foliage leaves and scaly leaves .

Foliage leaves area unit pinnately compound and having 500-100 leaflets organized within the rachis .The leaflets area unit sessile and have single unbranced vein .

The leaflet is harden .Scaly leaves organized alternate wit hfoliage leaves .They are brown ,hard persistant and non-photosynthetic.

Secondary Growth:

The mature traditional root shows secondary growth on each the lateral sides of primary vascular tissue. aspect|in conjunction with|beside|at the side of|together with} the inner side of primary bast develops the cambium. It cuts off secondary bast on outer facet and secondary vascular tissue on the inner facet. when someday the cells of the pericycle opposite to the protoxylem strands conjointly become meristematic and behave as cambium, cutting bast on the outer facet and vascular tissue on the inner facet.

Thus, an entire ring of cambium is created that forms an entire ring of secondary vascular tissue on the inner facet and complete ring of secondary bast on the outer facet. the first bast is crushed within the due course of development and seems within the type of crushed layer higher than the secondary bast.

Simultaneously the formation of periderm conjointly starts. The cells of the outmost layer of the cortex become meristematic (also referred to as cork cambium) and begin cutting cork cells on the outer facet and secondary cortex on the inner facet. within the course of the formation of cork, the cells of the epiblema area unit crushed

Internal Sructure of Root  :-

Normal root:
Epiblema:

It is the outmost limiting layer and consists of single layer of skinny walled cells. a number of its cells create to root hairs.

Cortex:

Epiblema surrounds the multilayered zone of skinny walled parenchymatous cortex with various living thing areas. The cells of the cortex area unit stuffed with starch. Some tannic acid cells, mucilage cells and generally sphaeraphides (calcium salt crystals) also are gift within the cortex. The innermost layer of the cortex forms the endodermis that is characterized by the presence of casparian strips.

Normal Root -Cycas

Vascular tissue:

Endordermis is followed by multilayered parenchymatous pericycle. tube bundles area unit radial. vascular tissue is diarch and exarch i. e., protoxylem is towards the periphery). The protoxylem consists of spiral tracheids whereas the metaxylem consists of scalariform thickenings. Vessels area unit absent. Alternating with the protoxylem teams area unit gift bast cells consisting of sieve tubes and bast parenchyma. The companion cells area unit fully absent.

Coralloid Root:

Epidermis:

In young root, it's like traditional root. However, in previous root the outmost tissue is periderm. It consists of two to five layers of dead cells.

b. Cortex:

The cortex is wider compared with the traditional root. A green protoctist zone is gift nearly within the middle of the cortex and divides it into outer cortex and inner cortex (Fig. 9A, B).

The protoctist zone consists of loosely connected, radially elongated skinny walled cells occupied by blue chlorophyte (Anabaena cycadae, blue-green algae punctiforme, Oscillatoria), microorganism (Azotobacter, bacteria genus radicicola) and a few fungi. the most perform of those roots is organic process because of the presence of cyanophycean members. Endodermis is comparable to traditional root

Corlloid Root -Cycas

Vascular tissue:

Endodermis is followed by multilayered parenchymatous pericycle. tube bundles area unit radial. vascular tissue is triarch and exarch.

Secondary growth is incredibly rare or absent. No secondary vascular tissue or secondary bast area unit developed though cork and cork cambium area unit gift.

Stem:

Epidermis:

It is the outmost layer of the stem. it's created of succinctly organized thick walled cells. cuticle is burst because of the armour of persistent leaf bases .

Cortex:

Epidermis encloses the cortex. It forms the main portion of the stem. it's composed of parenchymatous cells that area unit stuffed with sizable amount of starch grains. These starch grains area unit the supply of amylum starch. Therefore, C. revoluta is popularly referred to as amylum palm.

Cycas Stem

Scattered within the cortex area unit varied mucilage canals. every mucilage canal is lined by several radially elongated animal tissue or body fluid cells .which secrete mucilage. These canals area unit connected with those of the pith with the assistance of the medullary rays. The innermost layer of cortex is endodermis. it's not distinct.

Vascular Bundle :

The tube cylinder is enclosed by not terribly conspicuous pericycle. Like angiosperm stems tube cylinder consists of the many conjoined, collateral, open, endarch tube bundles organized in a very ring (ectophloic slphonostele). The vascular tissue consists of tracheids and vascular tissue parenchyma .

Vessels area unit absent. Outside the vascular tissue is that the bast that consists of sieve tubes and bast paraenchyma. Companion cells area unit absent. The vascular tissue is separated from the bast with the assistance of primary combium. The cells of the first cambium area unit brick formed.

The cells lying in between the tube bundles type the medullary rays. These area unit parenchymatous and connect the pith with the cortex. every vascular tissue is one celled wide and one to twenty cells long.

Pith:

In the centre of the stem is gift giant canals leaf traces large pith consisting of parenchymatous cells that area unit made in starch (sago starch). an outsized variety of mucilage canals also are gift, that area unit specifically similar in structure with the mucilage canals gift within the cortex.

Rachis:

Epidermis:

It is the outmost covering. it's created of succinctly organized thick walled cells. it's single bedded, coated with thick cuticle and has stomata.

Hypodermis:

Epidermis is followed by layer. it's differentiated into outer 2-3- layers of parenchyma (Chlorophyll containing skinny walled cells) and inner 4-6 layers of sclerenchyma (thick walled, hard cells.

Rachis in Cycas

Ground tissue:

Below the sclerenchyma is gift an outsized tissue created of skinny walled parenchymatous cells. it's referred to as ground tissue. during this region area unit gift several sticky canals and tube bundles.

Vascular bundles:

Vascular bundles area unit organized within the form of inverted Greek letter ‘omega’ .Each fibrovascular bundle is conjoined, collateral, endarch, open and diploxylic i. e., consists of centripetal and centrifugal vascular tissue and is enclosed by bundle sheath.

Xylem is gift towards the inner facet and consists of tracheids and vascular tissue parenchyma. Vessels area unit absent. bast is gift towards the outer facet of the fibrovascular bundle. It consists of sieve tubes and bast parenchyma. Companion cells area unit absent, Cambium is gift in between the vascular tissue and bast.

Leaflet:-

Epidermis:

It is the outer most single layer created of square cells. The higher cuticle is complete whereas the lower cuticle is interrupted by many sunken stomata gift within the region of the wings. The higher and lower cuticle is roofed by a thick layer of culicle.

Leaflet internal 

b. Hypodermis:

Below the cuticle happens the thick walled sclerenchymatous layer. it's single bedded within the region of blade however within the region of middle rib it becomes 2-3 bedded thick. 2 to 5 layers of sclerenchymatous cells also are gift higher than the lower cuticle solely within the region of the middle rib. It helps in checking the speed of transpiration and protects the tissue from excessive heat.

c. Mesophyll:

A well-developed mesophyll tissue is gift within the leaflet. it's differentiated into palisade tissue and spongy parenchyma. Palisade tissue is gift within the type of continuous layer below the sclerenchymatous layer. Spongy parenchyma gift solely within the wings directly higher than the lower cuticle. it's created of loosely organized oval cells stuffed with plastid. These cells have several living thing areas stuffed with air.

Vascular bundle:

A single giant fibrovascular bundle is gift within the middle rib region of the leaflet. it's enclosed by one layer of sclerenchymatous cells, referred to as bundle sheath. The fibrovascular bundle is conjoined, collateral, open and diploxylic. vascular tissue is gift towards the dorsal surface and bast is gift towards the ventral surface.

Xylem and bast area unit separated by a non-functional strip of cambium. Centrifugal vascular tissue is delineate by 2 little teams on either facet of the protoxylem. The remaining area of the fibrovascular bundle is stuffed with skinny walled parenchymatous cells.

Structure of microsporophyll:

Each sporophyl represents a reproductive structure. it's a planate, woody and triangular structure. it's differentiated into higher or distal, sterile region referred to as apophysis and proximal wedge formed fertile half. every sporophyl bears many hundred microsporangia (pollen sacs) on its dorsal surface (more than 1000).

Male Cone

Microsporangia area unit organized in clusters of three to six. every cluster or cluster of microsporangia is named sorus. In between the microsporangia covering hairs area unit gift that facilitate within the dispersion of the microspores and defend young sporangia.

Female procreative Organs:

Female procreative organs area unit megasporophylls. every feminine plant per annum produces various megasporophylls in acropetal succession higher than every crown of foliage and scaly leaves. there's no feminine cone formation. the quantity of the megasporophylls is way quite the quantity of the foliage leaves on the stem.

During the formation of the megasporophylls the top plant tissue isn't ran down like that of male cone and thus, the expansion of the stem continues, and therefore in feminine plant growth is monopodial.

Structure of Megasporophyll:

Each sporophyll (carpel) is thought to be a changed leaf. it's regarding twelve.7 cm to 25.4 cm long and might be divided into three parts: higher ivied portion, middle ovule bearing portion and lower stalk. Ovules area unit fashioned on the lateral facet of the center portion. The higher portion is pinnated and every pinna is tapering to some extent.

Structure of Megasporophyll

Two lateral rows of ovules area unit gift on the lateral facet of the center portion. 

In {cycas|Cycas|genus gymnosperm genus|gymnosperm genus} there's a good variation concerning the pinnated character of sporophyll and also the variety of ovules per foliage as a result of that in varied species of Cycas gradual reduction in megasporophylls will be derived.

The megasporophylls of C. revolula area unit pinnated whereas those of C. circinalis C. rumphii and C. beddomei area unit ovate pointed structures. In C. pectinata and C. siamensis they're orbicular or parallelogram structures .

The bedded portion is well developed in C. revoluta, C.pectinata and C. siamensis however reduced in C. circinalis, C. beddomei and C. rumphii .The margin of plate is serrate or rough in C.circinalis, C.beddomei and C. rumphii. the quantity of ovules take issue in several species of gymnosperm genus. It is 1-6. pairs in C.revoluta, C. Circinalis and just one try in C. norambyana. Megasporophylls area unit coated by yellow or brown hairs.