Spirogyra is a typical example for chlorophyceae (green algae).

Systematic Position (5    Kingdom Classification)

 Kingdom: Plantae

Division: Thallophyta

Class: Chlorophyceae

Order :Conjugales

Family :Zygnamaceae

Genus: Spirogyra

Species: zonata 

Occurrence

Spirogyra is cosmopolitan in distribution. It is a common, free floating thallous mass of filaments. It is a filamentous fresh water algae growing abundantly in ponds, pool, ditches, slow running rivers and streams.

Fig: Habit sketch of Spirogyra

They are most commonly known as pond scum or pond silk or water silk.

Vegetative Structure 

• The plant body is thallus which is multicellular, unbranched, filamentous, silky thread like structure.


• The filaments may range from few millimetres to several metres in length.


• Spirogyra filaments develop basal cell that helps in the attachment to the substratum known as hapteron or holdfast.


• They are green and mucilaginous.


• The cells of each filament is arranged linearly in end to end manner.


• 
  All the cells of filament are capable of division and growth.
  
  
  

Structure of Cell 

Each cell of Spirogyra consists of a cell wall and a mass of protoplasm.

• The cell wall is two layered, outer layer is made up of the pectin while the inner layer is made of the cellulose.


• 
  The pectin substance gelatinise, while dissolved in water  forms a slimy mucilaginous seath around the cells and filaments. It makes the filaments slippery in touch and slimy in appearance.
  


• Inner to cell wall there is a presence of selectively permeable membrane called cell membrane which encloses protoplasm.


• The protoplasm is differentiated into nucleus and cytoplasm. It has centrally located nucleus suspended through cytoplasmic strands.

• Cytoplasm is a colourless, granulated, viscous mass that contains membrane bounded cell organelles like mitochondria, plastids, Golgi bodies, ribosome, etc. Cytoplasm is located towards periphery and the large central portion is occupied by vacuole.


• The chloroplasts are spirally twisted or band shaped. The name of the algae is after the spiral arrangement of chloroplasts.


• In each ribbon- like chloroplasts, there occur nodules like protein bodies that store starch which are called pyrenoids.


• The number of chloroplasts in a cell is variable and may range from 1 to 16.