What is Cycas?

The stem is unbranched and straight. The leaf bases are strong, woody, and long-lasting. The stem becomes rougher as a result. The apex of the stem is surrounded by a clump of brown scales. The stem’s base is covered in pinnate compound leaves. The stem develops at a glacial rate. It grows a cluster of leaves every year. Older leaves fall off after two years.

Leaves and scales: In the axils, leaves develop near the tips of the scales. Each leaf is made up of a petiole, rachis, and lateral pinnae. The juvenile leaves have circinate vernation. Scales are also created every year. As a result, the green leaf clusters alternate with the scale clusters. Scales are tenacious as well. The surface of the old stem is coated in scales and leaf bases.

Morphology

Roots: The major root is still present in Cycas. Tuberous growth occurs. Cycas produces coralloid roots. Coralloid roots have tiny tufts and are dichotomously branching. These roots have an endophytic alga in the inner region of their cortex. Bacteria can be detected in the cortex on occasion. Bacteria fix nitrogen in the cells. The cortex’s parenchymatous tissue is made up of a variety of cells.

Primary vascular bundles exist within the cortex. They form a circle around the pitch in the centre. These packs are intended to be used as backups. The primary medullary rays are located between the neighbouring bundles.

Cambium is found in each vascular bundle as a narrow band. Endarches include the xylem. The presence of woody leaf bases on the surface adds to the strength of the stem.

The cortex’s periphery produces phellogen. It produces cork beneath the persistent leaf bases (peridium).

Internal Leaf Structure

Each pinna of a leaf has a characteristic bifacial structure in the transverse section.

I. The leaf’s surface is covered by a single layered epidermis. The upper epidermis cells have a little thicker wall than the lower epidermis cells. The walls of the lower epidermis, on the other hand, are thin. Sunken stomata can be seen at the bottom of the epidermis. A layer of hypodermis exists beneath the top epidermis. The mesophyll is separated by an upper palisade layer and a lower spongy parenchyma. Chloroplasts are abundant in mesophyll cells.

Tissues are located at the mid-ribs. They cause lateral conduction in the leaf. The vascular bundles are surrounded by the pericycle and endodermis.

The cortex is thick and made up of parenchymatous cells. Endodermis and pericycle surround the vascular tissues. Pith can be discovered in the centre of the stele. There is a root cap at the tip. Coralloid roots have a similar architecture. The presence of a blue green alga, on the other hand, causes the cortex of these roots to become disorganised. Geotropically negative coralloid roots

Reproduction

Cycas is a dioecious species. Male and female plants are maintained separate. Cycas plants can also reproduce vegetatively on occasion. On the stem, it develops a lot of buds. These buds develop into new plants.

Cones of Males

On male plants, male cones are formed. Each year, the number of cones created fluctuates from one to many. The shape of each male cone is fusiform. A centre axis runs through each cone. There are a lot of spirally arranged microsporophyll on it. The texture of the microsporophylls is woody. They have a wedge form to them. Microsporangia (Pollen sacs) cover the microsporophylls’ lower surface. Sod is formed by sporangia. Each sorus has two to six sporangia clusters. Several hundred sporangia are found in each sporophyll. Cycas produces a significant amount of spores.

The microspore cut off the lateral prothallial cell towards one side of the spore. The larger cell then cuts off a small generative cell adjacent to the prothallial cell. It itself be

Female Gametophyte

The megaspore (embryo sac) enlarges in size. Its nucleus undergoes many nuclear divisions. Thus several nuclei are formed in the megaspore. These nuclei occupy the peripheral region of the cytoplasm in the megaspore. Then the nuclei are surrounded by a cell wall. Thus the megaspore becomes multicellular. It gives rise to the female gametophyte. The cells of the gametophyte develop numerous starch grains. The original megaspore wall persists around the prothallial tissue.

Male Gametophyte

The pollen grain resumes its development after pollination. Generative cell divides into a stalk cell and a body cell. Both these cells represent an antheridium. A pollen tube grows out of the pollen grain. It penetrates the nucellus. The pollen grain becomes dormant at this stage. This period lasts for about four months. After that the pollen grain resumes its activity. Two blepharoplasts appear on the two sides of the nucleus. These blepharoplasts develop cilia. The body cell then divides into two antherozoids. The antherozoid develops thousands of cilia. The nucleus of each antherozoid enlarges and completely fills the whole of the antherozoid. Antherozoids remain motile for several hours.

Development of Embryo and Seed

Oospore divides into 200-300 cells. The cells of the central region disorganized to produce a cavity. This cavity is surrounded by two to three layers of cells. The cells in the lower region elongate very much to form a suspensor. The cells at the tip of the suspensor develop into the embryo. The elongating suspensor pushes the developing embryo deep into the prothallial tissue. These tissues provide nutrition to the developing embryo. Whole of the nucleus is consumed during the development of the embryo. Some prothallial tissue persists in the seed and forms an endosperm. A thick pad of tissue develops near the micropylar end. It functions as coleorhiza. Coleorhiza protects the radical of the embryo. Ovule is transformed into a seed. Embryo has two cotyledons. They occupy the whole seed. The seeds germinate immediately. Cotyledons remain within the seed of germination. It absorbs nutrients for the developing embryo.

Conclusion

The plant genus Cycas is part of the Cycadophyta, a very old lineage that is not closely linked to palms, ferns, trees, or any other contemporary group of plants. They are permanent evergreens that attained their greatest diversity during the Jurassic and Cretaceous eras, when they were found practically everywhere. The majority of cycas in the Northern Hemisphere perished together with the non-avian dinosaurs at the end of the Cretaceous period.

The only recognised extant genus in the family Cycadaceae is Cycas, which is also its type genus. There are about 113 accepted species.