SCYTONEMA​

CLASSIFICATION OF SCYTONEMA

Sub-division :- Algae

Class :- Myxophyceae

Order :- Nostocales

Family :- Scytonemataceae

Genus :- Scytonema

The genus Scytonema is usually found in sub-aerial habitats such as damp walls, brick-work, bark of the trees, etc. Filaments are interwoven to form a felt-like mass of considerable extent. Few species grow best on damp soil and others on the dripping surfaces of rocky cliffs.

EXTERNAL FEATURES OF THALLUS​

COMMENTS :-

• Filaments occur singly. The trichomes are enveloped in a sheath. 
• Filaments show false branching, branches being single or geminate (in pairs). 
• The trichomes are of the same diameter throughout its length. 
• The trichome is covered by an individual sheath which is firm and either hyaline or coloured. It may be homogeneous or lamellated.
• Heterocysts occupy intercalary position. It may be either single, in twos or threes. These are approximately of the same size as those of vegetative cells. Lateral branches are generally produced in between heterocysts. 
• Heterocysts show two shining granules, one each in contact with the cells on either side. It is pale yellow in colour and contents are homogenous.
• Cell structure is typically cyanophycean. Central part known as centroplasm is enclosed by peripheral pigmented chromatoplasm. The centroplasm has genetic material in the form of DNA. The chromatoplasm has scattered pigments and cyanophycean granules.

STUDY OF HORMOGONIA

COMMENTS :-

• Sexual reproduction is absent.
• Akinetes are asexual reproductive bodies. These are of rare occurrence. 
• Hormogones are found very commonly. They are solitary and terminal. 
• Hormogone is a spherical structure that is covered by a thick mucilaginous envelope.

IDENTIFICATION OF SCYTONEMA​

• Sub-division – Algae
  1. Thallus simple,
  2. Chlorophyll present.
  3. Cell walls of cellulose.  
• Class – Myxophyceae
  1. Chromatophore not organised, pigments diffused, blue-green.
  2. Photosynthetic reserve cyanophycean starch.
  3. True nucleus absent.
  4. Sexual reproduction absent.
• Order – Nostocales
  1.  Thallus with trichomes, unbranched, or with false branching.
  2. Hormogones, heterocysts, exospores and endospores generally present.  
• Family – Scytonemataceae
  1.  Trichomes uniseriate, without marked attenuation.
  2. Filaments always free, with false branching.
  3. Sheath firm, enclosing one or more trichomes.
• Genus – Scytonema
  1. Filaments with heterocysts.
  2. One trichome within a sheath.
  3. False branching present.
  4. Branches arising in pairs.