418 Annals New York Academy of Sciences 



Plectonema may show scytonematoid branching. In Symploca, the sheaths 

 are discrete and contain one trichome; adhering filaments form fascicles at 

 the surface of the plant. The sheaths of Phormidium are thin, hyaline, and 

 become diffluent. 



General Ecology 



Ecological studies on the Myxophyceae are quite limited. Most attention 

 has been given to the collection of organisms from a variety of habitats and 

 some information is available on their geographical distribution. In general, 

 the blue-green algae occur in all parts of the world where light and water are 

 available. Individual species may be distributed in the various climatic 

 zones, but others are found at extreme limits of the environment, from cold 

 regions such as the Antarctic or in the cryoconite of Greenland (Gerdel and 

 Drouet, 1960), and from the low elevation of the Dead Sea to mountains over 

 14,000 feet in altitude. They are a part of the salt marsh flora (Chapman, 

 1960), occur in extremely saUne Great Salt Lake (Flowers), hard and soft 

 waters (Palmer, 1959) and hot, dry desert soils (Cameron, 1961; KiUian and 

 Feher, 1939). Planktonic forms, frequently a single species, may grow pro- 

 lifically in favorable seasons when nitrates and phosphates are high and in some 

 cases release obnoxious toxins (Prescott, 1959). Aquatic species have also 

 been found in the lower subUttoral zone where Ught intensity is low (Ruttner, 

 1953), and in hot springs where the temperature may reach 86° C. (Kaplan, 

 1956). Other aquatic habitats can include industrial wastes with a high con- 

 tent of metals and acids (Palmer, 1959). More exotic habitats include associa- 

 tions with animals such as sponges, corals, and snails. In barren, eroded soil, 

 on wood, in sewage, on and under light transmitting rocks, and even in areas 

 of comparatively recent volcanic activity (Treub, 1888), it has been found that 

 blue-green algae are able to grow and survive. Furthermore, it has been de- 

 termined that the Eh range of blue-green algae is from —0.200 to +0.700 volts 

 and the ^H from 1.5 to 11 (Baas Becking et al., 1960). That they can resist 

 desiccation for decades has been shown in the revival of species from old, stored 

 soils (Bristol, 1919). Reproduction can be quite rapid, and oscillatorioid 

 forms can develop macroscopic growth in a few hours on desert soil which has 

 remained dry for a number of years. Prolonged resistance to desiccation has 

 been found in a dried herbarium specimen of nonsporeforming Nostoc commune 

 previously revived after 88 years of storage (Lipman, 1944), and later revived 

 after an additional time period of 19 years (Cameron, in press). Resistance is 

 also found to low temperatures. At —80° C, algae, in combination with 

 fungi as Uchens have been found to survive, and at —30° C. to even photo- 

 synthesize slowly (James, 1955). Parasitism of certain species of blue-green 

 algae by fungi is not uncommon (Drouet, 1954), and where optimal conditions 

 prevail for one of the organisms, the other is overwhelmed. The association 

 between the alga and the fungus in forming and maintaining the hchen is ex- 

 ceedingly complex and although the alga excretes antibiotic substances, the 

 fungus can have a lethal effect on the alga (Henriksson, 1961). 



Environmental conditions which are most favorable for the entire group of 

 blue-green algae are difficult to determine and correlate. Many species have 

 been named as distinct on the basis of the kind of environment in which they 



