Spirogyra

Life history of Spirogyra

CLASSIFICATION

Division- chlorophyta

Class. – chorophyceae

Order. – zygnematales

Family. – zygnemataceae

Genus. – spirogyra

INTRODUCTION

It is one of the commonest of green filamentous algae abundant in spring. It includes about 289 species and of these 94 has been reported from India. They are universal distribution but are relatively rare in the tropics. Of this various species S. condensata is commonly met with.

Occurrence

It is found in bright green, free-floating masses in the fresh water. It is found growing abundantly in fresh water ponds, pools, lakes, ditches, and also in slow flowing streams. In some species growing in running water, a short unicellular organ of attachment, called hapteron is formed. Spirogyra adnata is an attached form and found in flowing waters. Because of the slippery feel of the threads Spirogyra is often called the Pond-scum or Water silk. S. maxima, S, longata and S. nitido are some of the common species.

Thallus structure

It is thallus which consists of a long green cylindrical thread about 1/10 mm across and several centimetres long, filament. Each spirogyra plant possess filamentous structure. The filamentous are unbranched. Normally the filaments are free living, free floating and slimy and each consists of a few hundred similar cylindrical cella placed end to ond in a single row. There is no basa! distal differentiation, S. adnata and S. jogensis however, are exceptions. The basal coll in these species functions as an attaching organ. It developa rhizoidal outgrowths which assist in attaching the filament to the substratum. S. rhizopus and S rhizobrachialis, S. dubia and S. affinis also have rhizoids.

CELL STRUCTURE

The cell comprising the filament is cylindrical in form with transverso end walls. They are usually much longer than hroad. The cell has the structure typical of aparenchymatous cell. It consists of two parts, the cell wall and the protoplast

Cell wall

It surrounds the protoplast and thus forms its boundary. It is protective in function. The Cell wall is made up of two layers. The inner layer is cellulose in nature. It forms complete envelops around the protoplast. However, external layer envelops an inner layer which is the pectose layer. The outermost portion of pectos changes into pectin. The latter dissolves in water to form a slimy sheath. This mucilage sheath is sometimes referred to as the third layer of the cell wall it makes the filament feel slippery to touch. Because of the slippery feel of the thronds Spirogyra is often called the Pond – seum or Water silk.

Protoplast

The protoplast is differentiated into plasms membrane, cytoplast, one or more chloroplast with pyrenoids and a large central

The plasma membrane surrounds the cytoplast. The outer cytoplast forms a thin lining or a peripheral layer in contact with cell wall. It is also encloses a large central vacuole filled with cell sap, known as inner cytoplast. Inner cytoplast is often rich in tannins and other organic and inorganic compounds in solution. The sap vacuole is separated from the surrounding cytoplast by a thin, semipermeable membrane, the tonoplast. Embedded in the cytoplast and parietal in position are the large conspicuous chloroplast. They vary in number in different species from one to as many as fifteen in each cell.

Each chloroplast is an elongated, green helical band lying against the wall (parietal). It runs in a spiral manner and anticlockwise direction from one end of the cell to other. Because of Spiral chloroplast fenture the genus known as Spirogyra. All the chloroplast in the cell may be loosely or tightly coiled and run spirally in parallel. The band-shaped chloroplast or ribbon shaped chloroplast possess series of small, spherical, rounded bodies known as Pyrenoids. They lies equidistance from one another.