A.Classification
Some of the common Indian species of equisetum are E.debile , E.arvense etc
B.Structure of the sporophyte
1. External Structure- The sporophyte i.e., the plant body is well differentiated into- stem, leaves and roots-
Stem- The stem is underground, horizontal and much branched, which often penetrates more than a meter into the soil. The rhizome is jointed and provided with nodes and internodes. It gives off two types of branches sterile and fertile branches.
Sterile branches are green in color , persistent and have a whorl of lateral branches at each node. Sterile branches are vegetative in function. Fertile branches are generally unbranched, non green in colour, and short lived and bears a single strobilus at it's tip.
Leaves- leaves are small , slender, scale- like and each is provided with a single midrib. They are arranged in whorls at each node. They are fused at the base and free at the tip which forms a teeth like structure. They form a cup like structure at the base of internodes.
Roots- Roots are slender , much branched and adventious. They occur only at the nodes of the rhizome or stem bases.
2. Internal structure-
a) T.S of aerial stem- The internal structure of aerial stem shows the following tissue system-
Epidermis- Epidermis is singled layered and it's cell wall heavily silicified. Stomata are present in the cell of epidermis.
Cortex- Cortex is broad and diffrentiated into four zones-
c) T.S of roots- The root in transverse section shows epiblema, cortex and Stele.
Each cone or strobillus consists of a thick central axis upon which several densely crowded peltate appendage called sporangiophores are arranged in whorls. Each sporangiate is a stalked peltate structure projecting at right angles from the cone axis. Each sporangiate bears on the underside an elongated sac like structure called sporangia.
Mature sporangium is an elongated, cylindrical structure with a rounded apex. It consists of a delicate, one cell thick jacket layer. Inside the jacket layer is a mass of sporogenous tissue, from which some of the cells differentiates into spore mother cells and some gets degenerated.
The spore mother cells by meiotic divisions forms haploid spore tetrad. Equisetum is normally homosporous, and with the formation of spores, gametophytic generation begins.
If condition for growth are favourable, the first sex organs are formed when the gametoohytes are 30-40 days old. Archegonia first appear in meristematic margin of the gametophyte, in the regions where the upright lobes are developed. Antheridia generally begin to develop in large number, on the marginal regions of the gametoohyte after the development of the archegonia. They generally develop on the photosynthetic lobes or besides the archegonia.
Divisions-Sphenophyta
Class-Sphenopsida
Order-Equisitales
Family-Equisitaceae
Genus-Equisetum
Equisetum is commonly knows as horsetails comprises about 25 species and is world wide in distribution. Equisetum can grow in wide variety of habitats. Some species grow in damp and shaded place, other grow in ponds or marshes or in Sandy oil, near tha bank of river, etc. Some other are found to grow exposed dry habitats, along the road sides and railway embankments.Some of the common Indian species of equisetum are E.debile , E.arvense etc
B.Structure of the sporophyte
1. External Structure- The sporophyte i.e., the plant body is well differentiated into- stem, leaves and roots-
Stem- The stem is underground, horizontal and much branched, which often penetrates more than a meter into the soil. The rhizome is jointed and provided with nodes and internodes. It gives off two types of branches sterile and fertile branches.
Sterile branches are green in color , persistent and have a whorl of lateral branches at each node. Sterile branches are vegetative in function. Fertile branches are generally unbranched, non green in colour, and short lived and bears a single strobilus at it's tip.
Leaves- leaves are small , slender, scale- like and each is provided with a single midrib. They are arranged in whorls at each node. They are fused at the base and free at the tip which forms a teeth like structure. They form a cup like structure at the base of internodes.
Roots- Roots are slender , much branched and adventious. They occur only at the nodes of the rhizome or stem bases.
 |
| Source Wikipedia |
2. Internal structure-
a) T.S of aerial stem- The internal structure of aerial stem shows the following tissue system-
Epidermis- Epidermis is singled layered and it's cell wall heavily silicified. Stomata are present in the cell of epidermis.
Cortex- Cortex is broad and diffrentiated into four zones-
- An outermost cortex made of sclerenchymatous cells,
- Middle cortex made of chlorenchymatous cell,
- An inner cortex made of thin wall parenchymatic cells. The innermost layer of the cortex is the single layered endodermis with casparian strips.
Stele- Beneath the endosermis lie the Stele. Stele is dissescted siohonostele. Vascular bundle are aaranged in ring. Each bundle has three small strands of xylem and between which lies the phloem strands. The centre is occupied by a hollow pith containing water.
 |
| Source Wikipedia |
b) T S of rhizome- The rhizome in transverse section shows similiar structure like that of aerial stem except the following difference such as,
- Absence of stomata in the Epidermis,
- Cortex is divoid of photosynthetic chlorenchyma and sclerenchyma is poorly developed
- Pith may be solid or hollow.
c) T.S of roots- The root in transverse section shows epiblema, cortex and Stele.
Cortex is divided into two layers- an outer thick walled zone farming exodermis and an inner thin walled parenchymatous zone farming endodermis. Endodermis is two layer of cells thick.
Stele varies from triarch to tetrarch. Metaxylem lies in the centre.
 |
| Source Wikipedia |
C. Reproduction
The sporophyte of equisetum reproduce both by vegetative means and by production of spores.
1. Vegetative reproduction-
Vegetative reproduction takes place by following methods.
a) By tubers- In some species, a round or avoid tubers are developed in the rhizome. When detached from the parent rhizome each tubers grow into a new plant and thus serves as a means of Vegetative propogation of the sporophyte.
b) By branch primordia- Every branch of the rhizome bears performed branch premordial which can develop into new sub-terranean and aerial branches at any time, after the decay of older rhizome.
2. Spore Formation- In equisetum spore are formed on a specialized spore bearing structure known as strobili.
Strobilus i.e., cone aries singly at the apices of fertile shoots. The primitive type of cone is sub-sessile and is apiculate while the advanced type is stalked with rounded Apex. In some species, there is a ring like outfrowth at the base of cone, called annulus.
Each cone or strobillus consists of a thick central axis upon which several densely crowded peltate appendage called sporangiophores are arranged in whorls. Each sporangiate is a stalked peltate structure projecting at right angles from the cone axis. Each sporangiate bears on the underside an elongated sac like structure called sporangia.
The number of sporangia per sporangiophore varies from 5-10.
Mature sporangium is an elongated, cylindrical structure with a rounded apex. It consists of a delicate, one cell thick jacket layer. Inside the jacket layer is a mass of sporogenous tissue, from which some of the cells differentiates into spore mother cells and some gets degenerated.
The spore mother cells by meiotic divisions forms haploid spore tetrad. Equisetum is normally homosporous, and with the formation of spores, gametophytic generation begins.
 |
| Source Wikipedia |
D. Structure of gametophytes -
Spore is the first cell of gametophytes. A mature spore is globular in shape and provided with four concentric wall layer, such as
- Innermost delicate layer of cellulose known as endospore (intine),
- Next to the endospores lies externally exospores (exine),
- Exospores is externally surrounded by a delicate layer known as middle layer and
- The outermost thick epispore or episporium. The epispore is differentiated into four narrow, spirally wounded bands with flat and spoon like tips. These bands are commonly called elaters. The spiral bands remain tightly coiled about the spore until the sporangium dehisceand. These elaters are extremely hygroscopic and respond quickly changes in air moisture. Their expansion possibly assists in dehesience of the sporangium and also in spore dispersal.
Under favourable condition, the spore germinates and gives rise to normally monoecious gametophytic plant body.
The mature gametoohyte are long lived green, thalloid and branched structure which grow on the wet soil and shaded reigions. They show two well marked regions-
a) Cushions like compact and colourless basal regions and
b) The vertically erect, green photosynthetic , irregularly shaped lobed. Rhizoids arise on the lower surface of the basal portion.
If condition for growth are favourable, the first sex organs are formed when the gametoohytes are 30-40 days old. Archegonia first appear in meristematic margin of the gametophyte, in the regions where the upright lobes are developed. Antheridia generally begin to develop in large number, on the marginal regions of the gametoohyte after the development of the archegonia. They generally develop on the photosynthetic lobes or besides the archegonia.
 |
| Source Wikipedia |
1. Archegonium- The mature archegonium has a venter embedded in the gametophyte and a projecting neck. The neck is short and consists of four vertical rows of cells. The neck consists of 1-2 neck canal cells. The venter consists of a venter canal cell and an egg cell.
2. Antheredium- The antheredium is more or less rounded structure. It consists of an outer jacket layer, one celled in thickness and an inner androgonial cell.
The primary androgonial cell divides and redivides forming a group of androgonial cells which forms androcyte mother cells. Each androcyte i.e sperm mother cell metamorphosed into a large, flattened, spirally coiled and multiflagellate sperm i.e., spermatozoid. Sperms are set free at maturity by the breaking down of the jacket layer.
The primary androgonial cell divides and redivides forming a group of androgonial cells which forms androcyte mother cells. Each androcyte i.e sperm mother cell metamorphosed into a large, flattened, spirally coiled and multiflagellate sperm i.e., spermatozoid. Sperms are set free at maturity by the breaking down of the jacket layer.
 |
| Source Wikipedia |
Fertilization - At the time of fertilization one of the sperm swims towards the neck of the mature archegonium, then passes through the passage estaished by the dissolution of the neck canal cell and the ventral canal cell and finally fuses with the eeg.
As soon as the fusion take place , zygote (2n) develops.
As soon as the fusion take place , zygote (2n) develops.
With the formation of zygote the diploid generation (2n) begins.
0 Comments
If you have any query let me know.