MORPHOLOGY OF REPRESENTATIVE BLUE-GREEN ALGAE 



Roy E. Cameron 



Jel Propulsion Laboratory, California Inslilule of Technology, Pasadena, Calif. 



The blue-green algae, of the phylum Gyanophyta or Schizophyta, belong to 

 the class designated variously as the Cyanophyceae, Schizophyceae, or Myxo- 

 phyceae, and are plants of a gelatinous, stony, mealy, or leathery nature. 

 They are tirm or soft, extremely tough, and impregnated with salts or mucus 

 and easily disrupted when the gelatinous material surrounding them is of slight 

 viscosity. Their forms vary in size from micro- to macroscopic and in shape 

 they occur as spheres, cushions, strata, or cyhnders. The growth habit is 

 frequently centripetal, and depending on the inherent characteristics of the 

 plant and its environment, the adult plant can be a single cell and of less than 

 1 /x in diameter or a spreading plant of up to 1 m. in extent. They are cosmo- 

 politan in nature and are found chiefly on soil and in water but also in a variety 

 of other habitats wherever moisture, temperature, energy supply (sunlight), 

 />H, biogenic salts, respiratory gases (CO2 and O2), and other conditions for 

 growth and reproduction are favorable. They share with the bacteria a 

 unique ability to survive, as well as reproduce, at the extreme limits of the 

 natural environment. 



The blue-green algae are considered to be an ancient group of plants ex- 

 tending back to the Archeozoic (Tilden, 1935) although the geological record 

 is difficult to determine because they have few hard parts. The evidence of 

 their presence is attributed frequently to calcareous and sihcious strata and 

 cushions and very ancient deposits of tufa, marl, travertine, and sinter de- 

 veloped by activities of mainly filamentous forms (Drouet, in press). The 

 fossil remains that have been attributed to blue-green algae have not provided 

 evidence as to their evolutionary sequence (Fritsch, 1942). 



Characteristics of blue-green algae show that they resemble nonalgae as well 

 as other algae. Because they resemble bacteria in some respects, i.e., in 

 having no organized nuclei or true cell walls and a similar mode of cell division, 

 they have been classified as coordinate with the bacteria in the Schizophyceae 

 (Breed el al., 1958). It is also known that both groups contain members that 

 produce spores, and some have demonstrated the ability to fix atmospheric 

 nitrogen. Most contain a ,a'-diaminopimehc acid, and their concurrence in 

 similar ecological habitats and in cultures attests to similarities in certain 

 physiological characteristics. Sufficient differences, however, are found for 

 separation of bacteria from blue-green algae. Blue-green algae are rarely 

 parasitic, pigmentation is not comparable with that of the bacteria, oxygen is 

 evolved as a result of photosynthesis, movement is of a gUding or oscillating 

 nature — there are no flagella — and the size range of cells and plants is much 

 greater. Heterotrophic, colorless forms of blue-green algae usually can be 

 attributed to bacteria or fungi which have been misinterpreted (Drouet, in 

 press), unless one accepts an organism such as Beggialoa as a colorless form 

 (Pringsheim, 1949). Morphologically, the Myxophyceae show a greater 

 structural complexity and diversity than bacteria, but less so than other algal 



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